Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing a rule that would reduce air pollution from highway heavy-duty vehicles and engines, including ozone, particulate matter, and greenhouse gases. This proposal would change the heavy-duty emission control program—including the standards, test procedures, useful life, warranty, and other requirements—to further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy-duty engines. Heavy-duty vehicles and engines are important contributors to concentrations of ozone and particulate matter and their resulting threat to public health, which includes premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. This proposal would reduce emissions of nitrogen oxides and other pollutants. In addition, this proposal would make targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program, proposing that further GHG reductions in the MY 2027 timeframe are appropriate considering lead time, costs, and other factors, including market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector. We also propose limited amendments to the regulations that implement our air pollutant emission standards for other sectors ( e.g., light-duty vehicles, marine diesel engines, locomotives, various types of nonroad engines, vehicles, and equipment).

DATES:

Comments: Written comments must be received on or before May 13, 2022. Under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of consideration if the Office of Management and Budget (OMB) receives a copy of your comments on or before April 27, 2022.

Public Hearing: EPA plans to hold a virtual public hearing on April 12, 2022. An additional session may be held on April 13, 2022. Please refer to Participation in Virtual Public Hearing in the SUPPLEMENTARY INFORMATION section for additional information on the public hearing.

ADDRESSES:

You may send comments, identified by Docket ID No. EPA-HQ-OAR-2019-0055, by any of the following methods:

• Federal eRulemaking Portal: https://www.regulations.gov/ (our preferred method) . Follow the online instructions for submitting comments.

• Email: a-and-r-Docket@epa.gov . Include Docket ID No. EPA-HQ-OAR-2019-0055 in the subject line of the message.

• Mail: U.S. Environmental Protection Agency, EPA Docket Center, OAR, Docket EPA-HQ-OAR-2019-0055, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.

• Hand Delivery or Courier (by scheduled appointment only): EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operations are 8:30 a.m.-4:30 p.m., Monday-Friday (except Federal Holidays).

Instructions: All submissions received must include the Docket ID No. for this rulemaking. Comments received may be posted without change to https://www.regulations.gov/ , including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the “Public Participation” heading of the SUPPLEMENTARY INFORMATION section of this document. Out of an abundance of caution for members of the public and our staff, the EPA Docket Center and Reading Room are open to the public by appointment only to reduce the risk of transmitting COVID-19. Our Docket Center staff also continues to provide remote customer service via email, phone, and webform. Hand deliveries and couriers may be received by scheduled appointment only. For further information on EPA Docket Center services and the current status, please visit us online at https://www.epa.gov/dockets .

Public Hearing. EPA plans to hold a virtual public hearing for this rulemaking. Please refer to Participation in Virtual Public Hearing in the SUPPLEMENTARY INFORMATION section for additional information.

FOR FURTHER INFORMATION CONTACT:

Brian Nelson, Assessment and Standards Division, Office of Transportation and Air Quality, Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105; telephone number: (734) 214-4278; email address: nelson.brian@epa.gov .

SUPPLEMENTARY INFORMATION:

A. Public Participation

Written Comments

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2019-0055, at https://www.regulations.gov (our preferred method), or the other methods identified in the ADDRESSES section. Once submitted, comments cannot be edited or removed from the docket. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets .

Due to public health concerns related to COVID-19, the EPA Docket Center and Reading Room are open to the public by appointment only. Our Docket Center staff also continues to provide remote customer service via email, phone, and webform. Hand deliveries or couriers will be received by scheduled appointment only. For further information and updates on EPA Docket Center services, please visit us online at https://www.epa.gov/dockets .

The EPA continues to carefully and continuously monitor information from the Centers for Disease Control and Prevention (CDC), local area health departments, and our Federal partners so that we can respond rapidly as conditions change regarding COVID-19.

Participation in Virtual Public Hearing

Please note that because of current CDC recommendations, as well as state and local orders for social distancing to limit the spread of COVID-19, EPA cannot hold in-person public meetings at this time.

The EPA plans to hold a virtual public hearing on April 12, 2022. An additional session may be held on April 13, 2022. This hearing will be held using Zoom. In order to attend the virtual public hearing, all attendees (including those who will not be presenting verbal testimony) must register in advance. EPA will begin registering speakers for the hearing upon publication of this document in the Federal Register . To register, please use the registration link that will be available on the EPA rule web page once registration begins: https://www.epa.gov/regulations-emissions-vehicles-and-engines/proposed-rule-and-related-materials-control-air-1 . A separate registration form must be submitted for each person attending the hearing.

The last day to register to speak at the hearing will be five working days before the first public hearing date. The EPA will post a general agenda for the hearing with the order of speakers at: https://www.epa.gov/regulations-emissions-vehicles-and-engines/proposed-rule-and-related-materials-control-air-1 . This agenda will be available no later than two working days before the first public hearing date.

In order to allow everyone to be heard, EPA is limiting verbal testimony to three minutes per person. Speakers will not be able to share graphics via the virtual public hearing. Speakers will be able to request an approximate speaking time as part of the registration process, with preferences considered on a first-come, first-served basis. EPA also recommends submitting the text of oral comments as written comments to the rulemaking docket.

EPA will make every effort to follow the schedule as closely as possible on the day of the hearing; however, please plan for the hearings to run either ahead of schedule or behind schedule.

The EPA may ask clarifying questions during the oral presentations, but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public hearing.

Please note that any updates made to any aspect of the hearing will be posted online at: https://www.epa.gov/regulations-emissions-vehicles-and-engines/proposed-rule-and-related-materials-control-air-1 . While the EPA expects the hearing to go forward as described here, please monitor our website or contact Tuana Phillips, (202)-565-0074, phillips.tuana@epa.gov to determine if there are any updates. The EPA does not intend to publish a document in the Federal Register announcing updates.

If you require the services of a translator or special accommodations such as audio description, please identify these needs when you register for the hearing or by contacting Tuana Phillips at (202)-565-0074, phillips.tuana@epa.gov . EPA may not be able to arrange accommodations without advance notice.

B. General Information

Does this action apply to me?

This action relates to companies that manufacture, sell, or import into the United States new heavy-duty highway engines. Additional amendments apply for gasoline refueling facilities and for manufacturers of all sizes and types of motor vehicles, stationary engines, aircraft and aircraft engines, and various types of nonroad engines, vehicles, and equipment. Regulated categories and entities include the following:

This table is not intended to be exhaustive, but rather provides a guide for readers regarding entities likely to be regulated by this action. This table lists the types of entities that EPA is now aware could potentially be regulated by this action. Other types of entities not listed in the table could also be regulated. To determine whether your entity is regulated by this action, you should carefully examine the applicability criteria found in Sections XII and XIII of this preamble. If you have questions regarding the applicability of this action to a particular entity, consult the person listed in the FOR FURTHER INFORMATION CONTACT section.

What action is the agency taking?

The Environmental Protection Agency (EPA) is proposing a rule that would reduce air pollution from highway heavy-duty vehicles and engines. This proposal would change the heavy-duty emission control program—including the standards, test procedures, regulatory useful life, emission-related warranty, and other requirements—to further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy-duty engines. Heavy-duty vehicles and engines are important contributors to concentrations of ozone and particulate matter and their resulting threat to public health, which includes premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. This proposal would reduce emissions of nitrogen oxides and other pollutants. In addition, this proposal would make targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program, proposing that further GHG reductions in the MY 2027 timeframe are appropriate considering lead time, costs, and other factors, including market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector.

What is the agency's authority for taking this action?

Section 202(a)(1) of the Clean Air Act requires the EPA to set emission standards for air pollutants from new motor vehicles or new motor vehicle engines, which the Administrator has found cause or contribute to air pollution that may endanger public health or welfare. See Sections I.A.4, I.F, and XIV of this preamble for more information on the agency's authority for this action.

What are the incremental costs and benefits of this action?

We compare total monetized health benefits to total costs associated with the proposed Options 1 and 2 in Section IX. Our results show that annual benefits of the proposed Option 1 would be larger than the annual costs in 2045, a year when the program would be fully implemented and when most of the regulated fleet would have turned over, with annual net benefits of $9 and $31 billion assuming a 3 percent discount rate, and net benefits of $8 and $28 billion assuming a 7 percent discount rate. Annual benefits would also be larger than annual costs in 2045 for the proposed Option 2, although net benefits would be lower than from the proposed Option 1 (net benefits of proposed Option 2 would be $6 and $23 billion at a 3 percent discount rate, and net benefits of $5 and 21 billion at a 7 percent discount rate). See Section VIII for more details on the net benefit estimates. For both the proposed Options 1 and 2, benefits also outweigh the costs when expressed in present value terms and as equalized annual values.

Did EPA conduct a peer review before issuing this action?

This regulatory action was supported by influential scientific information. Therefore, EPA conducted peer reviews in accordance with OMB's Final Information Quality Bulletin for Peer Review. Specifically, we conducted peer reviews on five analyses: (1) Analysis of Heavy-Duty Vehicle Sales Impacts Due to New Regulation (Sales Impacts), (2) Exhaust Emission Rates for Heavy-Duty Onroad Vehicles in MOVES_CTI NPRM (Emission Rates), (3) Population and Activity of Onroad Vehicles in MOVES_CTI NPRM (Population and Activity), (4) Cost teardowns of Heavy-Duty Valvetrain (Valvetrain costs), and (5) Cost teardown of Emission Aftertreatment Systems (Aftertreatment Costs). These peer reviews were all letter reviews conducted by a contractor. The peer review reports for each analysis are located in the docket for this action and at EPA's Science Inventory ( https://cfpub.epa.gov/si/ ).

Table of Contents

ES. Executive Summary

A. Purpose of the Regulatory Action

B. Overview of the Regulatory Action

C. Summary of the Major Provisions in the Regulatory Action

D. Projected Emission Reductions, Air Quality Improvements, Costs, and Benefits

E. Summary of Specific Requests for Comments

I. Introduction

A. Brief Overview of the Heavy-Duty Truck Industry

B. History of Emission Standards for Heavy-Duty Engines and Vehicles

C. Petitions to EPA for Additional NO_X Emissions Control

D. California Heavy-Duty Highway Low NO_X Program Development

E. Advance Notice of Proposed Rulemaking

F. EPA Statutory Authority for the Proposal

G. Basis of the Proposed Standards

II. Need for Additional Emissions Control

A. Background on Pollutants Impacted by This Proposal

B. Health Effects Associated With Exposure to Pollutants Impacted by This Proposal

C. Environmental Effects Associated With Exposure to Pollutants Impacted by This Proposal

III. Proposed Test Procedures and Standards

A. Overview

B. Summary of Compression-Ignition Exhaust Emission Standards and Duty Cycle Test Procedures

C. Summary of Compression-Ignition Off-Cycle Standards and In-Use Test Procedures

D. Summary of Spark-Ignition Heavy-Duty Engine Exhaust Emission Standards and Test Procedures

E. Summary of Spark-Ignition Heavy-Duty Vehicle Refueling Emission Standards and Test Procedures

IV. Compliance Provisions and Flexibilities

A. Regulatory Useful Life

B. Ensuring Long-Term In-Use Emissions Performance

C. Onboard Diagnostics

D. Inducements

E. Certification Updates

F. Durability Testing

G. Averaging, Banking, and Trading

H. Early Adoption Incentives

I. Compliance Options for Generating NO_X Emission Credits From Electric Vehicles

J. Fuel Quality

K. Other Flexibilities Under Consideration

V. Program Costs

A. Technology Package Costs

B. Operating Costs

C. Program Costs

VI. Estimated Emission Reductions From the Proposal and Alternatives

A. Emission Inventory Methodology

B. Estimated Emission Reductions From the Proposed Criteria Pollutant Program

C. Estimated Emission Reductions From the Alternatives Analyzed

D. Evaluating Emission Impacts of Electric Vehicles in the Proposed Emission Inventory Baseline

VII. Air Quality Impacts of the Proposed Rule

A. Ozone

B. Particulate Matter

C. Nitrogen Dioxide

D. Carbon Monoxide

E. Air Toxics

F. Visibility

G. Nitrogen Deposition

H. Demographic Analysis of Air Quality

VIII. Benefits of the Program

IX. Comparison of Benefits and Costs

A. Methods

B. Results

X. Economic Impact Analysis

A. Impact on Vehicle Sales, Mode Shift, and Fleet Turnover

B. Employment Impacts

XI. Targeted Updates to the HD GHG Phase 2 Heavy-Duty Greenhouse Gas Emissions Program

A. Background on Heavy-Duty Greenhouse Gas Emission Standards

B. What has changed since we finalized the HD GHG Phase 2 rule?

C. Proposed Changes to HD GHG Phase 2 CO₂ Standards for Targeted Subcategories

D. HD GHG Phase 2 Advanced Technology Credits for CO₂ Emissions

E. Emissions and Cost Impacts of Proposed Revised MY 2027 CO₂ Emission Standards

F. Summary of Proposed Changes to HD GHG Phase 2

XII. Other Amendments

A. General Compliance Provisions (40 CFR Part 1068) and Other Cross-Sector Issues

B. Heavy-Duty Highway Engine and Vehicle Emission Standards (40 CFR Parts 1036 and 1037)

C. Fuel Dispensing Rates for Heavy-Duty Vehicles (40 CFR Parts 80 and 1090)

D. Refueling Interface for Motor Vehicles (40 CFR Parts 80 and 1090)

E. Light-Duty Motor Vehicles (40 CFR Parts 85, 86, and 600)

F. Large Nonroad Spark-Ignition Engines (40 CFR Part 1048)

G. Small Nonroad Spark-Ignition Engines (40 CFR Part 1054)

H. Recreational Vehicles and Nonroad Evaporative Emissions (40 CFR Parts 1051 and 1060)

I. Marine Diesel Engines (40 CFR Parts 1042 and 1043)

J. Locomotives (40 CFR Part 1033)

K. Stationary Compression-Ignition Engines (40 CFR Part 60, Subpart IIII)

L. Heavy-Duty Compression-Ignition Engines (40 CFR Part 86)

XIII. Executive Orders Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Paperwork Reduction Act (PRA)

C. Regulatory Flexibility Act (RFA)

D. Unfunded Mandates Reform Act (UMRA)

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

G. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR Part 51

J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations.

XIV. Statutory Provisions and Legal Authority

Executive Summary

A. Purpose of the Regulatory Action

The Environmental Protection Agency (EPA) is proposing a multipollutant rule to further reduce air pollution from heavy-duty engines and vehicles across the United States, including ozone and particulate matter (PM). In addition, as part of this rulemaking we are proposing targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program (HD GHG Phase 2). This proposed rulemaking builds on and improves the existing emission control program for on-highway heavy-duty engines and vehicles. This proposal is pursuant to EPA's authority under the Clean Air Act to regulate air pollutants emitted from mobile sources. The proposal is also consistent with Executive Order (E.O.) 14037, which directed EPA to consider setting new oxides of nitrogen (NO_X) emission standards and updating the existing GHG emissions standards for heavy-duty engines and vehicles. In this proposed action, EPA is co-proposing two regulatory options for new NO_X standards: Proposed Option 1 and proposed Option 2. As discussed in Section B.1 of this Executive Summary and throughout this preamble, we request comment on the options presented, as well as the full range of options between them.

Heavy-duty (HD) engines operating across the U.S. emit NO_X and other pollutants that contribute to ambient levels of ozone, PM, and NO_X . These pollutants are linked to premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. Data show that heavy-duty engines are important contributors to concentrations of ozone and PM_2.5 and their resulting threat to public health.

The proposed rulemaking would change key provisions of the heavy-duty emission control program—including the standards, test procedures, regulatory useful life, emission-related warranty, and other requirements; the two regulatory options (proposed Options 1 and 2) would result in different numeric levels of the standards and lengths of useful life and warranty periods. The proposed Options 1 and 2 and the range between them provide the numeric values for these key provisions that we focus on for this proposal. Together, the key provisions in the proposal would further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy-duty engines (see Section I.B for an overview of the proposed program). The requirements in the proposed Option 1 and the proposed Option 2 would lower emissions of NO_X and other air pollutants (PM, hydrocarbons (HC), air toxics, and carbon monoxide (CO)) beginning as early as model year (MY) 2027. The emission reductions from both the proposed Option 1 and the proposed Option 2 would increase over time as more new, cleaner vehicles enter the fleet.

We estimate that if finalized as proposed, the proposed Option 1 would reduce NO_X emissions from heavy-duty vehicles in 2040 by more than 50 percent; by 2045, a year by which most of the regulated fleet would have turned over, heavy-duty NO_X emissions would be more than 60 percent lower than they would have been without this action. Our estimates show proposed Option 2 would reduce heavy-duty NO_X emissions in 2045 by 47 percent (see Section I.D for more information on our projected emission reductions from proposed Option 1 or 2). These emission reductions would result in air quality improvements in ozone and PM_2.5; we estimate that in 2045, the proposed Option 1 would result in total annual monetized ozone- and PM_2.5 -related benefits of $12 and $33 billion at a 3 percent discount rate, and $10 and $30 billion at a 7 percent discount rate. In the same calendar year, proposed Option 2 would result in total annual monetized ozone- and PM_2.5 -related benefits of $9 and $26 billion at a 3 percent discount rate, and $8 and $23 billion at a 7 percent discount (see Section VIII for discussion on quantified and monetized health impacts). Given the analysis we present in this proposal, we currently believe that Option 1 may be a more appropriate level of stringency as it would result in a greater level of achievable emission reduction for the model years proposed, which is consistent with EPA's statutory authority under Clean Air Act section 202(a)(3). These emission reductions would result in widespread decreases in ambient concentrations of pollutants such as ozone and PM_2.5 . These widespread projected air quality improvements would play an important role in addressing concerns from states, local communities, and Tribal governments about the contributions of heavy-duty engines to air quality challenges they face such as meeting their obligations to attain or continue to meet National Ambient Air Quality Standards (NAAQS), and to reduce other human health and environmental impacts of air pollution.

In addition to further reducing emissions of NO_X and other ozone and PM_2.5 precursors, as part of this rulemaking we are proposing targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program (HD GHG Phase 2). The proposed updates would apply to certain CO₂ standards for MYs 2027 and later trucks that are appropriate considering lead time, costs, and other factors, including market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector. The proposed updates are intended to balance further incentivizing zero and near-zero emissions vehicle development with ensuring that the standards achieve an appropriate fleet-wide level of CO₂ emissions reductions.

1. Industry Overview

Heavy-duty highway vehicles (also referred to as “trucks” in this preamble) range from vocational vehicles that support local and regional construction, refuse collection, and delivery work to long-haul tractor-trailers that move freight cross-country. This diverse array of vehicles is categorized into weight classes based on gross vehicle weight ratings (GVWR) that span Class 2b trucks and vans greater than 8,500 lbs GVWR through Class 8 long-haul tractors and other commercial vehicles that exceed 33,000 lbs GVWR. These vehicles are primarily powered by diesel-fueled, compression-ignition (CI) engines, although gasoline-fueled, spark-ignition (SI) engines are common in the lighter weight classes, and smaller numbers of alternative fuel engines ( e.g., liquified petroleum gas, compressed natural gas) are found in the heavy-duty fleet. Vehicles powered by electricity, either in the form of battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs) are also increasingly entering the heavy-duty fleet. The operational characteristics of some commercial applications ( e.g., delivery vehicles) can be similar across several vehicle weight classes, allowing a single engine, or electric power source in the case of BEVs and FCEVs, to be installed in a variety of vehicles. For instance, engine specifications needed for a Class 4 parcel delivery vehicle may be similar to the needs of a Class 5 mixed freight delivery vehicle or a Class 6 beverage truck. Performance differences needed to operate across this range of vehicles can be achieved through adjustments to chassis-based systems ( e.g., transmission, cooling system) external to the engine.

2. The Need for Additional Emission Control of NO_X and Other Pollutants From Heavy-Duty Engines

Across the U.S., NO_X emissions from heavy-duty engines are important contributors to concentrations of ozone and PM_2.5 and their resulting health effects. Heavy-duty engines will continue to be one of the largest contributors to mobile source NO_X emissions nationwide in the future, representing 32 percent of the mobile source NO_X emissions in calendar year 2045. Furthermore, it is estimated that heavy-duty engines would represent 89 percent of the onroad NO_X inventory in calendar year 2045. Reducing NO_X emissions is a critical part of many areas' strategies to attain and maintain the ozone and PM NAAQS; many state and local agencies anticipate challenges in attaining the NAAQS, maintaining the NAAQS in the future, and/or preventing nonattainment (see Section II). Some nonattainment areas have already been “bumped up” to higher classifications because of challenges in attaining the NAAQS.

In addition, emissions from heavy-duty engines can significantly affect individuals living near truck freight routes. Based on a study EPA conducted of people living near truck routes, an estimated 72 million people live within 200 meters of a truck freight route (see discussion in Section II.B.7). Relative to the rest of the population, people of color and those with lower incomes are more likely to live near truck routes (see Sections II.B and VII.H for additional discussion on our analysis of environmental justice impacts of this proposal). This population includes children, and in addition, childcare facilities and schools can be in close proximity to freight routes.

Clean Air Act section 202(a)(3)(A) requires EPA to set emission standards for NO_X, PM, HC, and CO that reflect the greatest degree of emission reduction achievable through the application of technology that will be available for the model year to which such standards apply. Although heavy-duty engines have become much cleaner over the last decade, catalysts and other technologies have evolved such that harmful air pollutants can be reduced even further.

Heavy-duty emissions that affect local and regional populations are attributable to several engine operating modes and processes. Specifically, the operating modes and processes projected to contribute the most to the heavy-duty NO_X emission inventory in 2045 are medium-to-high load (36 percent), low-load (28 percent), and aging (24 percent) ( i.e., deterioration and mal-maintenance of the engine's emission control system) (see Section VI for more information on projected inventory contributions from each operating mode or process). These data suggest that medium- and high-load operating conditions continue to merit concern, while also showing that opportunities for significant additional emission reductions and related air quality improvements can be achieved through provisions that encourage emission control under low-load operation and throughout an engine's operational life. Our approach for provisions that address these aspects of the emission inventory is outlined below and described in more detail in sections that follow.

As described in Section III, the standards in proposed Options 1 and 2 would reduce emissions during a broader range of operating conditions that span nearly all in-use operation. The standards in proposed Options 1 and 2 are based on technology improvements which have become available over the 20 years since the last major rule was promulgated to address emissions of NO_X, PM, HC, and CO (hereafter referred to as “criteria pollutants”) and toxic pollutants from heavy-duty engines. As further detailed in Section III, available data indicate that emission levels demonstrated for certification are not achieved under the broad range of real-world operating conditions. In fact, less than ten percent of the data collected during a typical test while the vehicle is operated on the road is subject to EPA's in-use, on-the-road emission standards. These testing data further show that NO_X emissions from heavy-duty diesel vehicles are high during many periods of vehicle operation that are not subject to current on-the-road emission standards. For example, “low-load” engine conditions occur when a vehicle operates in stop-and-go traffic or is idling; these low-load conditions can result in exhaust temperature decreases that then lead to the diesel engine's selective catalytic reduction (SCR)-based emission control system becoming less effective or ceasing to function. Test data collected as part of EPA's manufacturer-run in-use testing program indicate that this low-load operation could account for more than half of the NO_X emissions from a vehicle during a typical workday. Similarly, heavy-duty SI engines also operate in conditions where their catalyst technology becomes less effective, resulting in higher levels of air pollutants; however, unlike CI engines, it is sustained medium-to-high load operation where emission levels are less certain.

As noted in this Section A.2 of the Executive Summary, deterioration and mal-maintenance of the engine's emission control system is also projected to result in NO_X emissions that would represent a substantial part of the HD inventory in 2045. To address this problem, as part of our comprehensive approach, both proposed Options 1 and 2 include longer regulatory useful life and emission-related warranty requirements that would maintain emission control through more of the operational life of heavy-duty vehicles (see Section IV for more discussion on the proposed useful life and warranty requirements).

Reducing NO_X emissions from heavy-duty vehicles would address health and environmental issues raised by state, local, and Tribal agencies in their comments on the Advance Notice of Proposed Rule (ANPR). In addition to concerns about meeting the ozone and PM_2.5 NAAQS, they expressed concerns about environmental justice, regional haze, and damage to terrestrial and aquatic ecosystems. They mentioned the impacts of NO_X emissions on numerous locations, such as the Chesapeake Bay, Narragansett Bay, Long Island Sound, Joshua Tree National Park and the surrounding Mojave Desert, the Adirondacks, and other areas. Tribes and agencies commented that NO_X deposition into lakes is harmful to fish and other aquatic life forms on which they depend for subsistence livelihoods. They also commented that regional haze and increased rates of weathering caused by pollution are of particular concern and can damage culturally significant archeological sites.

3. The Historic Opportunity for Clean Air Provided by Zero-Emission Vehicles

We are at the early stages of a significant transition in the history of the heavy-duty on-highway sector—a shift to zero-emission vehicle (ZEV) technologies. This change is underway and presents an opportunity for significant reductions in heavy-duty vehicle emissions. Major trucking fleets, manufacturers and U.S. states have announced plans to transition the heavy-duty fleet to zero-emissions technology, and over just the past few years we have seen the early introduction of zero-emission technology into a number of heavy-duty vehicle market segments.

Executive Order 14037 identifies three potential regulatory actions for EPA to consider: (1) This proposed rule for heavy-duty vehicles for new criteria pollutant standards and strengthening of the Model Year 2027 GHG standards; (2) a separate rulemaking to establish more stringent criteria and GHG emission standards for medium-duty vehicles for Model Year 2027 and later (in combination with light-duty vehicles); and (3) a third rulemaking to establish new GHG standards for heavy-duty vehicles for Model Year 2030 and later. This strategy will establish the EPA regulatory path for the future of the heavy-duty vehicle sector, and in each of these actions EPA will consider the critical role of ZEVs in enabling stringent emission standards.

In addition to the proposed standards and requirements for NO_X and other air pollutant emissions, we are also proposing targeted revisions to the already stringent HD GHG Phase 2 rulemaking, which EPA finalized in 2016. The HD GHG Phase 2 program includes GHG emission standards tailored to certain regulatory vehicle categories in addition to heavy-duty engines including: Combination tractors; vocational vehicles; and heavy-duty pickup trucks and vans. The HD GHG Phase 2 program includes progressively more stringent CO₂ emission standards for HD engines and vehicles; these standards phase in starting in MY 2021 through MY 2027. The program built upon the GHG Phase 1 program promulgated in 2011, which set the first-ever GHG emission standards for heavy-duty engines and trucks.

When the HD GHG Phase 2 rule was promulgated in 2016, we established the Phase 2 GHG standards and advanced technology incentives on the premise that electrification of the heavy-duty market was unlikely to occur in the timeframe of the program. However, several factors have arisen since the adoption of Phase 2 that have changed our outlook for heavy-duty electric vehicles. First, the heavy-duty market has evolved such that in 2021, there are a number of manufacturers producing fully electric heavy-duty vehicles in a number of applications. Second, the State of California has adopted an Advanced Clean Trucks program that includes a manufacturer sales requirement for zero-emission truck sales, specifically that “manufacturers who certify Class 2b-8 chassis or complete vehicles with combustion engines would be required to sell zero-emission trucks as an increasing percentage of their annual California sales from 2024 to 2035.” Finally, other states have signed a Memorandum of Understanding establishing goals to increase the heavy-duty electric vehicle market. We are proposing that further GHG reductions in the MY 2027 timeframe are appropriate considering lead time, costs, and other factors, including these developments to zero-emission technologies in certain segments of the heavy-duty vehicle sector. We discuss the impacts of these factors on the heavy-duty market in Section XI. As outlined in Section I.B and detailed in Section XI, we are proposing to increase the stringency of the existing MY 2027 standards for many of the vocational vehicle and tractor subcategories, specifically those where we project early introduction of ZEVs. We are also considering whether it would be appropriate in the final rule to increase the stringency of the standards even more than what we propose for MYs 2027-2029, including the potential for progressively more stringent CO₂ standards across these three model years. Progressively strengthening the stringency of the standards for model years 2028 and 2029 could help smooth the transition to ambitious greenhouse gas standards for the heavy-duty sector starting as soon as model year 2030. We believe there is information and data that could support higher projected penetrations of HD ZEVs in the MY 2027 to 2029 timeframe and we request comment and additional supporting information and data on higher penetration rates, which could serve as the basis for the increase in the stringency of the CO₂ standards for specific Phase 2 vehicle subcategories. For example, what information and data are available that would support HD ZEV penetration rates of 5 percent or 10 percent (or higher) in this timeframe, and in what HD vehicle applications and categories. We are also requesting comment on an aspect of the HD GHG Phase 2 advanced technology incentive program.

EPA has heard from a number of stakeholders urging EPA to put in place policies to rapidly advance ZEVs in this current rulemaking, and to establish standards requiring 100 percent of all new heavy-duty vehicles be zero-emission no later than 2035. The stakeholders state that accelerating ZEV technologies in the heavy-duty market is necessary to prioritize environmental justice in communities that are impacted by freight transportation and already overburdened by pollution. One policy EPA has been asked to consider is the establishment of a ZEV sales mandate ( i.e., a nationwide requirement for manufacturers to produce a portion of their new vehicle fleet as ZEVs). EPA is not proposing in this action to establish a heavy-duty ZEV mandate. EPA in this action is considering how the development and deployment of ZEVs can further the goals of environmental protection and best be reflected in the establishment of EPA's standards and regulatory program for MY 2027 and later heavy-duty vehicles. As discussed earlier in this section, EPA will also be considering the important role of ZEV technologies in the upcoming light-duty and medium-duty vehicle proposal for MY 2027 and later, and in the heavy-duty vehicle proposal for MY 2030 and later. EPA requests comment under this proposal on how the Agency can best consider the potential for ZEV technologies to significantly reduce air pollution from the heavy-duty vehicle sector (including but not limited to the topic of whether and how to consider including specific sales requirements for HD ZEVs).

4. Statutory Authority for This Action

As discussed in Section I, EPA is proposing revisions to emission standards and other requirements applicable to emissions of NO_X, PM, HC, CO, and GHG from new heavy-duty engines and vehicles under our broad statutory authority to regulate air pollutants emitted from mobile sources, consistent with our history of using a multi-pollutant approach to regulating criteria pollutants and GHG emissions from heavy-duty engines and vehicles. Section 202(a)(1) of the Clean Air Act (CAA) requires the EPA to “by regulation prescribe (and from time to time revise) . . . standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines . . . , which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare”. Standards under CAA section 202(a) take effect “after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.” Thus, in establishing or revising CAA section 202(a) standards designed to reduce air pollution that endangers public health and welfare, EPA also must consider issues of technological feasibility, compliance cost, and lead time. EPA may consider other factors such as safety. There are currently heavy-duty engine and vehicle standards for emissions of NO_X, PM, HC, CO, and GHGs.

Under CAA section 202(a)(3)(A), standards for emissions of NO_X , PM, HC, and CO emissions from heavy-duty vehicles and engines are to “reflect the greatest degree of emission reduction achievable through the application of technology which the Administrator determines will be available for the model year to which such standards apply, giving appropriate consideration to cost, energy, and safety factors associated with the application of such technology.” Section 202(a)(3)(C) requires that these standards apply for no less than 3 model years and apply no earlier than 4 years after promulgation.

Emission standards set under CAA section 202(a) apply to vehicles and engines “for their useful life.” CAA section 202(d) directs EPA to prescribe regulations under which the useful life of vehicles and engines shall be determined, and for heavy-duty vehicles and engines establishes minimum values of 10 years or 100,000 miles, whichever occurs first, unless EPA determines that greater values are appropriate. CAA section 207(a) further requires manufacturers to provide an emissions warranty, and EPA set the current warranty periods for heavy-duty engines in 1983.

As outlined in this executive summary, the proposed program would reduce heavy-duty emissions through several major provisions pursuant to the CAA authority described in this section. Sections I.F and XIV of this preamble further discuss our statutory authority for this proposal; Section I.G further describes the basis of our proposed NO_X, PM, HC, CO, and GHG emission standards and other requirements. Section XIII describes how this proposal is also consistent with E.O. 14037, “Strengthening American Leadership in Clean Cars and Trucks” (August 5, 2021), which directs EPA to consider taking action to establish new NO_X standards for heavy-duty engines and vehicles beginning with model year 2027.

B. Overview of the Regulatory Action

Our approach to further reduce air pollution from highway heavy-duty engines and vehicles through the proposed program features several key provisions. We co-propose options to address criteria pollutant emissions from heavy-duty engines. In addition, this proposal would make targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program, proposing that further GHG reductions in the MY 2027 timeframe are appropriate considering lead time, costs, and other factors, including market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector. We also propose limited amendments to the regulations that implement our air pollutant emission standards for other sectors ( e.g., light-duty vehicles, marine diesel engines, locomotives, various types of nonroad engines, vehicles, and equipment). Our proposed provisions are briefly described in this Section I.B and summarized in Section I.C. We describe the proposed Options 1 and 2 in detail in the Sections III, IV, and XI. We discuss our analyses of estimated emission reductions, air quality improvements, costs, and monetized benefits of the proposed program in Section I.D below, and these are detailed in Sections V through X.

1. Overview of Criteria Pollutant Program

The proposed provisions to reduce criteria pollutant emissions can be thought of in three broad categories: (1) Controlling emissions under a broader range of engine operating conditions, (2) maintaining emission control over a greater portion of an engine's operational life, and (3) providing manufacturers with flexibilities to meet the proposed standards while clarifying our regulations. Specifically, provisions in the first category would include updated test procedures and revised emission standards, while those in the second category would include lengthened regulatory useful life and emission warranty periods, as well as several other updates to encourage proper maintenance and repair. These provisions would apply to heavy-duty engines used in Class 2b through 8 vehicles. Provisions in the third category would provide opportunities to generate NO_X emission credits that provide manufacturers with flexibilities to meet the proposed standards and encourage the introduction of new emission control technologies earlier than required. This category also includes our proposal to modernize our current regulatory text, including clarifications and updates for hybrid electric, battery-electric, and fuel cell electric heavy-duty vehicles.

Our discussion below focuses on the revised emission standards and useful life and warranty periods contained in two regulatory options that we are proposing: The proposed Option 1 and the proposed Option 2. Although we refer to the two regulatory options as the proposed Option 1 and the proposed Option 2, we are giving full consideration to both options, as well as the full range of options between them. Both the proposed Option 1 and the proposed Option 2 would begin in MY 2027, but the proposed Option 1 would have a second step in MY 2031. Overall, proposed Option 2 is less stringent than the MY 2031 standards in the proposed Option l because the proposed Option 2 has higher numeric NO_X emission standards and shorter useful life periods. As discussed in Section D of this Executive Summary and Section VI, we project proposed Option 1 would result in greater emission reductions than proposed Option 2; Section I.G summarizes the basis of our proposed Options 1 and 2 with details on our feasibility analysis for each option presented in Section III. In addition to the proposed Options 1 and 2, we present an alternative (the Alternative) that we also considered. The Alternative is more stringent than either the proposed Option 1 MY 2031 standards or the proposed Option 2 because the Alternative has shorter lead time, lower numeric NO_X emission standards and longer useful life periods. We note that we currently are unable to conclude that the Alternative is feasible in the MY 2027 timeframe over the useful life periods in the Alternative in light of deterioration in the emission control technologies that we have evaluated to date, and we expect that we would need additional supporting data or other information in order to determine that the Alternative is feasible in the MY 2027 timeframe to consider adopting it in the final rule.

The proposed Option 1 and proposed Option 2 generally represent the range of regulatory options, including the standards and test procedures, regulatory useful life and emission-related warranty periods and implementation schedules that we are currently considering in this rulemaking, depending in part on any additional comments and other information we receive on the feasibility, costs, and other impacts of the proposed Options 1 and 2. We request comment on all aspects of the proposed Options 1 and 2, or other alternatives roughly within the range of options covered by the proposed Options 1 and 2, including the revised emission standards and useful life and warranty periods, one and two-step approaches, model years of implementation and other provisions described in this proposal. Based on currently available information, in order to consider adopting the Alternative in the final rule, we believe we would need additional supporting data or other information to be able to conclude that the Alternative is feasible in the MY 2027 timeframe. We request comment, including relevant data and other information, related to the feasibility of the implementation model year, numeric levels of the emission standards, and useful life and warranty periods included in the Alternative, or other alternatives outside the range of options covered by the proposed Options 1 and 2.

We will continue learning about the capability and durability of engine and aftertreatment technologies through our ongoing technology evaluations, as well as any information provided in public comments on this proposal. Section III describes our plans for expanding on the analyses developed for this proposal.

2. Overview of Targeted Revisions to the HD GHG Phase 2 Program

In addition to the proposed criteria pollutant program provisions, we are proposing to increase the stringency of the existing GHG standards for MY 2027 trucks and requesting comment on updates to the advanced technology incentive program for electric vehicles. We propose updates to select MY 2027 GHG standards after consideration of the market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector. These proposed GHG provisions are based on our evaluation of the heavy-duty EV market for the MY 2024 through 2027 timeframe. While the HD Phase 2 GHG standards were developed in 2016 based on the premise that electrification of the heavy-duty market beyond low volume demonstration projects was unlikely to occur in the timeframe of the program, our current evaluation shows that there are a number of manufacturers producing fully electric heavy-duty vehicles in several applications in 2021—and this number is expected to grow in the near term. These developments along with considerations of lead time, costs and other factors have demonstrated that further GHG reductions in the MY 2027 timeframe are appropriate. We expect school buses, transit buses, delivery trucks (such as box trucks or step vans), and short haul tractors to have the highest EV sales of all heavy-duty vehicle types between now and 2030. We have given careful consideration to an approach that would result in targeted updates to reflect the emerging HD EV market without fundamentally changing the HD GHG Phase 2 program as a whole. Thus, we are proposing targeted updates to the HD Phase 2 GHG standards to account for the current electrification of the market by making changes to only those standards that are impacted by these four types of electric vehicles. We believe this proposal considered the feasibility of technologies, cost, lead time, emissions impact, and other relevant factors, and therefore these standards are appropriate under CAA section 202(a). We also are seeking comment on changes to the advanced technology credit program since the current level of HD GHG Phase 2 incentives for electrification may no longer be appropriate for certain segments of the HD EV market considering the projected rise in electrification. We provide an overview of this approach in this Section I.C and detail our proposal in Section XI.

C. Summary of the Major Provisions in the Regulatory Action

1. Controlling Criteria Pollutant Emissions Under a Broader Range of Engine Operating Conditions

In the first broad category of provisions to reduce criteria pollutant emissions in this rulemaking, we are proposing to reduce emissions from heavy-duty engines under a range of operating conditions through revisions to our emissions standards and test procedures. These revisions would apply to both laboratory-based standards and test procedures for both heavy-duty CI and SI engines, as well as the standards and test procedures for heavy-duty CI engines on the road in the real world.

i. Proposed Laboratory Standards and Test Procedures

For heavy-duty CI engines, we are proposing new standards for laboratory-based tests using the current duty cycles, the transient Federal Test Procedure (FTP) and the steady-state Supplemental Emission Test (SET) procedure. These existing test procedures require CI engine manufacturers to demonstrate the effectiveness of emission controls when the engine is transitioning from low-to-high loads or operating under sustained high load, but do not provide for demonstrating emission control under sustained low-load operations. We are proposing that laboratory demonstrations for heavy-duty CI engines would also include a new low-load cycle (LLC) test procedure to demonstrate that emission controls are meeting proposed LLC standards when the engine is operating under low-load and idle conditions. The proposed addition of the LLC would help ensure lower NO_X emissions in urban areas and other locations where heavy-duty vehicles operate in stop-and-go traffic or other low-load conditions.

For heavy-duty SI engines, we are proposing new standards for their laboratory demonstrations using the current FTP duty cycle, and updates to the current engine mapping procedure to ensure the engines achieve the highest torque level possible during testing. We are proposing to add the SET procedure to the heavy-duty SI laboratory demonstrations; it is currently only required for heavy-duty CI engines. Heavy-duty SI engines are increasingly used in larger heavy-duty vehicles, which makes it more likely for these engines to be used in higher-load operations covered by the SET. We are further proposing a new refueling emission standard for incomplete vehicles above 14,000 lb GVWR starting in MY 2027. The proposed refueling standard is based on the current refueling standard that applies to complete heavy-duty gasoline-fueled vehicles. Consistent with the current evaporative emission standards that apply for these same vehicles, we are proposing that manufacturers could use an engineering analysis to demonstrate that they meet our proposed refueling standard.

Our proposed Option 1 and proposed Option 2 NO_X emission standards for all defined duty cycles for heavy-duty CI and SI engines are detailed in Table 1. As shown, the proposed Option 1 NO_X standards would be implemented in two steps beginning with MY 2027 and becoming more stringent in MY 2031. The proposed Option 2 NO_X emission standards would be implemented with a single step in MY 2027. As noted in Section B.1 of this Executive Summary, overall, we consider proposed Option 2 to be less stringent than the standards in the proposed Option 1 because proposed Option 2 has higher numeric NO_X emission standards with similar useful life periods as the proposed Option 1 in MY 2027, and shorter length of useful life periods than the proposed Option 1 in MY 2031. In contrast, the Alternative is more stringent than proposed Option 1's MY 2031 standards (see Section III), and we currently do not have information to support the conclusion that the combination of shorter lead time, lower numeric levels of the standards and longer useful life periods in the Alternative is feasible in the MY 2027 timeframe based on the emission control technologies we have evaluated to date. See Section III for more discussion on feasibility. Consistent with our current approach for criteria pollutants, the standards in proposed Options 1 and 2, presented in Table 1, are numerically identical for SI and CI engines.

ii. Proposed On-the-Road Standards and Test Procedures

In addition to demonstrating emission control over defined duty cycles in a laboratory, heavy-duty CI engines must be able to demonstrate emission control over an undefined duty cycle while engines are in use on the road in the real world. Both proposed Options 1 and 2 include updates to the procedure for “off-cycle” testing, such that data collected during a wider range of operating conditions would be valid, and therefore subject to emission standards.

Similar to the current approach, emission measurements collected during off-cycle testing would be collected on a second-by-second basis. We are proposing the emissions data would be grouped into 300-second windows of operation. Each 300-second window would then be binned based on the type of operation that the engine performs during that 300-second period. Specifically, the average power of the engine during each 300-second window would determine whether the emissions during that window are binned as idle (Bin 1), low-load (Bin 2), or medium-to-high load (Bin 3).

Our proposed 3-bin approach would cover a wide range of operations that occur in the real world—significantly more in-use operation than today's requirements. Bin 1 would include extended idle and other very low-load operations, where engine exhaust temperatures may drop below the optimal temperature where SCR-based aftertreatment works best. Bin 2 would include a large fraction of urban driving conditions, during which engine exhaust temperatures are generally moderate. Bin 3 would include higher-power operations, such as on-highway driving that typically results in higher exhaust temperatures and high catalyst efficiencies. Given the different operational profiles of each of these three bins, we are proposing a separate standard for each bin. The proposed structure follows that of our current not-to-exceed (NTE) off-cycle standards, while covering a much broader range of engine operation.

Table 2 presents our proposed Option 1 and Option 2 off-cycle standards for NO_X emissions from heavy-duty CI engines. The proposed Option 2 off-cycle NO_X standards are higher (less stringent) and have a shorter useful life than the proposed Option 1 standards in MY 2031. For the Alternative, our assessment of currently available data indicates that the off-cycle standard for the medium/high load bin (Bin 3) would not be feasible in the MY 2027 timeframe, and additional or different technology would be necessary to meet the Alternative off-cycle standards. See Section III for details on the off-cycle standards for other pollutants in the proposed Options 1 and 2 and the Alternative.

In addition to the proposed standards for the defined duty cycle and off-cycle test procedures, the proposed Options 1 and 2 include several other provisions for controlling emissions from specific operations in CI or SI engines. First, we are proposing to allow CI engine manufacturers to voluntarily certify to the California Air Resources Board (CARB) clean idle standards by adding to EPA regulations an idle test procedure that is based on an existing CARB procedure. We are also proposing to require a closed crankcase ventilation system for all highway CI engines to prevent crankcase emissions from being emitted directly to the atmosphere. See Section III.B for more discussion on both the proposed idle and crankcase provisions. For heavy-duty SI, we are proposing refueling emission standards for incomplete vehicles above 14,000 lb GVWR (see Section III.E for more discussion).

2. Maintaining Criteria Pollutant Emission Control Over a Greater Portion of an Engine's Operational Life

Reducing emissions under a broad range of engine operating conditions is one category of our proposed program provisions. Maintaining emission control over a greater portion of an engine's operational life is the second broad category of proposed provisions. The major elements in this category include proposals to (1) extend the regulatory useful life of heavy-duty engines, (2) provide an opportunity for manufacturers to use rapidly aged parts necessary to demonstrate emission performance over the regulatory useful life, (3) lengthen emission warranty periods, and 4) increase the likelihood that emission controls will be maintained properly through more of the service life of heavy-duty engines. Our proposals for each of these elements is outlined below and detailed in Section IV; unless explicitly stated otherwise, proposals for each of these elements would apply under both proposed Options 1 and 2, as well as the full range of options in between them.

i. Proposed Useful Life Periods

EPA is proposing to increase the regulatory useful life mileage values for new heavy-duty engines to better reflect real-world usage, extend the emissions durability requirement for heavy-duty engines, and ensure certified emission performance is maintained throughout more of an engine's operational life. For proposed Option 1, Increases to useful life values for heavy-duty engines would apply in two steps, as discussed in Section IV.A. For the first step for CI engines, MY 2027 through 2030, we are proposing useful life mileage values that are approximately a midpoint between the current useful life mileages and our proposed CI engines MY 2031 and later mileages. For the second step, we are proposing useful life mileage values for MY 2031 and later CI engines that cover a majority of the estimated operational life mileages, but less than the first out-of-frame rebuild for these engines. The proposed Option 1 first step for SI engines in MY 2027 through 2030 would better align with the current useful life mileages for GHG emission standards applicable to these engines. The proposed Option 1 second step useful life mileage for SI engines for MY 2031 and later is based on the published engine service life for heavy-duty gasoline engines in the market today.

The useful life mileages in the proposed Option 2 are shorter than those in the proposed Option 1; we are giving full consideration to the useful life periods of proposed Options 1 and 2, and the range between the useful life periods in the proposed Options. Our proposed Option 1 and Option 2 useful life periods for heavy-duty CI and SI engines are presented in Table 3. See Section IV for the useful periods of the Alternative.

ii. Proposed Durability Demonstration Updates

The proposed longer useful life periods outlined in Table 3 would require manufacturers to extend their durability demonstrations, which show that the engines will meet applicable emission standards throughout their regulatory useful life. EPA regulations require manufacturers to include durability demonstration data as part of an application for certification of an engine family. Manufacturers typically complete this demonstration by following regulatory procedures to calculate a deterioration factor (DF).

To address the need for accurate and efficient emission durability demonstration methods, EPA worked with manufacturers and CARB to address this concern through guidance for MY 2020 and later engines. In Section IV.F, we propose three methods for determining DFs, consistent with the recent guidance, including a new option to bench-age the aftertreatment system to limit the burden of generating a DF over the proposed lengthened useful life periods. We also propose to codify in the EPA regulations three DF verification options available to manufacturers in recent guidance. The proposed verification options would confirm the accuracy of the DF values submitted by manufacturers for certification. We also introduce a test program to evaluate a rapid-aging protocol for diesel catalysts that we may consider as an option for CI engine manufacturers to use in their durability demonstration.

iii. Proposed Emissions Warranty Periods

EPA's current emission-related warranty periods range from 22 percent to 54 percent of regulatory useful life. As EPA is proposing to lengthen the useful life periods in this rulemaking, we are also proposing to lengthen the emission warranty periods and increase the fraction of useful life miles covered under warranty. These proposed revised warranty periods are expected to result in better engine maintenance and less tampering, helping to maintain the benefits of the emission controls. In addition, longer regulatory warranty periods may lead engine manufacturers to simplify repair processes and make them more aware of system defects that would be tracked and reported to EPA over a longer period.

In Section IV.B, we provide detailed discussion and request comment on these four ways that longer emission warranty periods may enhance long-term performance of emission-related devices and systems. We also discuss other impacts of lengthening regulatory emission warranty periods and other approaches that vary coverage and may similarly ensure long-term in-use emission performance.

EPA is proposing to lengthen the emissions warranty periods for all primary intended service classes to cover a larger portion of the operational lives of new heavy-duty engines. Our proposed Option 1 warranty mileages for MY 2031 are approximately 80 percent of the proposed useful life mileages. The proposed Option 1 MY 2027 through 2030 mileages are approximately midpoints between the current and proposed Option 1 MY 2031 and later mileages. The proposed Option 2 set of emission warranty periods would match CARB's Step 1 warranty periods that will already be in effect beginning in model year 2022 for engines sold in California. We believe the proposed Option 2 mileages represent an appropriate lower end of the range we are considering for the revised regulatory emission warranty periods. Our proposed Option 1 and proposed Option 2 emission warranty periods are presented in Table 4. See Section IV.B for updates in proposed Options 1 and 2 to our years-based warranty periods and add hours-based warranty periods for all engine classes to cover low average annual mileage applications. We also considered an alternative set of warranty periods that are presented in Section IV.B.

iv. Proposed Provisions To Ensure Long-Term Emissions Performance

In the ANPR, we introduced several ideas for an enhanced, comprehensive strategy to increase the likelihood that emission controls will be maintained properly through more of the operational life of heavy-duty engines, including beyond their useful life periods. Our proposed updates to maintenance provisions include defining the type of maintenance manufacturers may choose to recommend to owners in maintenance instructions, updating minimum maintenance intervals for certain critical emission-related components, and outlining specific requirements for maintenance instructions provided in the owner's manual.

We are proposing changes to the owner's manual and emissions label requirements to ensure access to certain maintenance information and improve serviceability. We expect this additional maintenance information to improve factors that contribute to mal-maintenance, which would result in better service experiences for independent repair technicians, specialized repair technicians, owners who repair their own equipment, and possibly vehicle inspection and maintenance technicians. We also believe that improving owner experiences with operating and maintaining heavy-duty engines can reduce the likelihood of tampering.

v. Proposed Inducement Provisions

ANPR commenters indicated that engine derates or “inducements” are a significant source of operator frustration. EPA currently has guidance on potential options manufacturers might utilize to meet existing requirements through an inducement strategy for their SCR-based aftertreatment system. We are proposing to codify inducement provisions after considering manufacturer designs and operator experiences with SCR-based aftertreatment systems. In Section IV.D, we present the key principles we followed in developing the proposed inducement provisions, which includes a focus on conditions that are within an operator's control, a multi-step derate schedule, and a backup check to override false inducements. We also include a detailed set of requests for comment highlighting the wide range of adjustments we are currently considering.

vi. Proposed Onboard Diagnostics Provisions

Onboard diagnostics (OBD) refer to systems of electronic controllers and sensors required by current regulation to detect malfunctions of engines and emission controls. EPA's existing OBD program, promulgated in 2009, allows manufacturers to demonstrate how the OBD system they have designed to comply with California OBD requirements also complies with the intent of the EPA OBD requirements. Although EPA maintains separate OBD regulations, all manufacturers currently seek OBD approval from CARB for OBD systems in engine families applying for 50-state certification, and then use this approval to demonstrate compliance with EPA requirements.

In Section IV.C, we are proposing to update our OBD regulations both to better address newer diagnostic methods and available technologies, and to streamline provisions where possible. We propose to incorporate by reference the existing CARB OBD regulations updated in 2019 as the starting point for our updated OBD regulations. We are proposing to exclude or revise certain CARB provisions that we believe are not appropriate for a federal program and are proposing to include additional elements to improve the usefulness of OBD systems for users (see Section IV.C for details).

EPA is specifically proposing additional OBD elements to improve the robustness and usefulness of OBD systems. These additional elements include emission system health monitors, an expanded list of publicly available OBD parameters, additional freeze frame data parameters, and enabling certain self-testing capabilities for owners. These proposed changes would benefit the environment by helping to reduce malfunctioning emission systems in-use through access to additional data that may be useful for service technicians, state and local inspection and maintenance operations, and owners.

3. Other Proposed Compliance Provisions and Flexibilities

In addition to the key program provisions, we are also proposing several provisions to provide manufacturers with flexibility to meet the proposed standards and encourage the introduction of new emission control technologies earlier than required; these provisions would apply under both proposed Options 1 and 2, as well as the full range of options in between them. These provisions include our proposal to migrate and update the compliance provisions of 40 CFR part 86, subpart A, to 40 CFR part 1036; continue averaging, banking, and trading (ABT) of credits generated against our heavy-duty engine criteria pollutant standards; provide incentives for early adoption of technologies to meet the standards; allow manufacturers to generate NO_X emission credits for hybrid electric, battery electric, and fuel cell electric vehicles (HEVs, BEVs, and FCEVs); and make limited amendments to regulations that implement our air pollutant emission standards for other industry sectors, including light-duty vehicles, light-duty trucks, marine diesel engines, locomotives, and various types of nonroad engines, vehicles, and equipment.

i. Proposed Migration From 40 CFR Part 86, Subpart A

Heavy-duty criteria pollutant regulations were originally codified into 40 CFR part 86, subpart A, in the 1980s. We believe this rulemaking provides an opportunity to clarify (and otherwise improve) the wording of our existing heavy-duty criteria pollutant regulations in plain language and migrate them to 40 CFR part 1036. Part 1036, which was created for the Phase 1 GHG program, provides a consistent, updated format for our regulations, with improved organization. In general, this migration is not intended to change the compliance program previously specified in part 86, except as specifically proposed in this rulemaking. See our summary of the proposed migration in Section III.A, and additional details in our memorandum to the docket. The proposed provisions of part 1036 would generally apply for model years 2027 and later, unless noted, and manufacturers would continue to use part 86 in the interim.

ii. Proposed Opportunities for NO_X Emission Credits

We are proposing targeted revisions to the current emissions ABT provisions to account for specific aspects of the broader proposed program. We are also proposing an early adoption incentive program that would recognize the environmental benefits of lower-emitting vehicles entering the fleet ahead of required compliance dates for the proposed standards. Through this optional program, manufacturers who demonstrate early compliance with the proposed MY 2027 or MY 2031 standards would apply a multiplier to emission credits generated under the proposed ABT program (see Section IV.H for details). We are also proposing to offer NO_X emission credits for HEVs, BEVs and FCEVs based on the near-zero or zero-tailpipe emissions performance of these technologies, for HEVs or BEVs and FCEVs, respectively, and after consideration of ANPR comments. We are choosing not to propose emission credit multipliers for HEVs, BEVs, and FCEVs. We believe that the potential loss of emission reductions that could result from providing credit multipliers is not justified in light of the current extent of technology development and implementation. Manufacturers choosing to generate NO_X emission credits from BEVs or FCEVs would need to conduct testing and meet durability requirements discussed in Section IV.

iii. Other Amendments

EPA has promulgated emission standards for highway and nonroad engines, vehicles, and equipment. Section XII of this proposed rule describes several amendments to correct, clarify, and streamline a wide range of regulatory provisions for many of those different types of engines, vehicles, and equipment. Section XII.A includes technical amendments to compliance provisions that apply broadly across EPA's emission control programs to multiple industry sectors, including light-duty vehicles, light-duty trucks, marine diesel engines, locomotives, and various other types of nonroad engines, vehicles, and equipment. Some of those amendments are for broadly applicable testing and compliance provisions in 40 CFR parts 1065, 1066, and 1068. Other cross-sector issues involve making the same or similar changes in multiple standard-setting parts for individual industry sectors. The rest of Section XII describes proposed amendments that apply uniquely for individual industry sectors.

We are proposing amendments in two areas of note for the general compliance provisions in 40 CFR part 1068. First, we are proposing to take a comprehensive approach for making confidentiality determinations related to compliance information that companies submit to EPA. We are proposing to apply these provisions for all highway, nonroad, and stationary engine, vehicle, and equipment programs, as well as aircraft and portable fuel containers.

Second, we are proposing provisions that include clarifying text to establish what qualifies as an adjustable parameter and to identify the practically adjustable range for those adjustable parameters. The proposed adjustable-parameter amendments also include specific provisions related to electronic controls that aim to deter tampering.

4. Targeted Revisions to the HD GHG Phase 2 Program

As noted at the start of this Section I.B, we have developed a proposed approach to make targeted updates that take into consideration the growing HD electric vehicle market without fundamentally changing the HD GHG Phase 2 program as a whole. These developments along with considerations of lead time, costs and other factors have demonstrated that further GHG reductions in the MY 2027 timeframe are appropriate. Specifically, we propose to adjust the HD GHG Phase 2 vehicle GHG emission standards by sales-weighting the projected heavy-duty EV production levels of school buses, transit buses, commercial delivery trucks, and short-haul tractors and by lowering the applicable emission standards in MY 2027 accordingly. We project these four vehicle types will have the highest EV sales of all heavy- duty vehicle types between now and 2030. Because these four EV vehicle types do not correspond directly with the specific subcategories for standards that we developed in HD GHG Phase 2 (subcategories differentiated by vehicle weight, use, fuel type, etc.), we use EPA certification data to determine which subcategories of standards would be impacted by EV production in MY 2027. By sales-weighing the projected production levels of the four EV vehicle types in 2027, our proposed approach adjusts 17 of the 33 MY 2027 Phase 2 vocational vehicle and tractor standards and does not change any MY 2021 or MY 2024 standards or any of the Class 2b/3 pickup truck and van standards. We request comment on the proposed approach to determine the threshold.

In addition to these proposed standard adjustments, we are requesting comment on options to update the advanced technology incentive program for electric and plug-in hybrid vehicles beginning in MY 2024. These changes may be appropriate to reflect that such levels of incentives for electrification may no longer be appropriate for certain segments of the HD EV market. We are trying to balance providing additional incentives for the continued development of zero and near-zero emission vehicles without inadvertently undermining the GHG emission reductions from the HD GHG Phase 2 program with inappropriate incentives.

D. Projected Emission Reductions, Air Quality Improvements, Costs, and Benefits

Our analysis of the estimated emission reductions, air quality improvements, costs, and monetized benefits of the proposed criteria pollutant program is outlined below and detailed in Sections V through X. While the discussion below generally focuses on our analysis of the proposed Option 1, we also discuss the proposed Option 2; additional information on analyses of proposed Options 1 and 2 is included in the sections that follow. As discussed in Section III, we currently lack information to show that the Alternative is feasible in the MY 2027 timeframe based on the emission control technologies that we have evaluated to date, and therefore we are not presenting an analysis of the costs or benefits of the Alternative. We expect that we would need additional data supporting the feasibility of the Alternative to further consider it in the development of the final rule.

The proposed provisions in Options 1 and 2, which are described in detail in Sections III and IV, are expected to reduce emissions from highway heavy-duty engines in several ways. We project the proposed emission standards for heavy-duty CI engines would reduce tailpipe emissions of NO_X; the combination of the proposed low-load test cycle and off-cycle test procedure for CI engines would help to ensure that the reductions in tailpipe emissions are achieved in-use, not only under high-speed, on-highway conditions, but also under low-load and idle conditions. We also project reduced tailpipe emissions of NO_X, CO, PM, VOCs, associated air toxics, and methane from the proposed emission standards for heavy-duty SI engines, particularly under cold-start and high-load operating conditions. The longer emission warranty and regulatory useful life requirements for heavy-duty CI and SI engines in the proposed Options 1 and 2 would help maintain the expected emission reductions for all pollutants, including primary exhaust PM_2.5, throughout the useful life of the engine. The onboard refueling vapor recovery requirements for heavy-duty SI engines in the proposed Options 1 and 2 would reduce VOCs and associated air toxics. Table 5 summarizes the projected reductions in heavy-duty emission from the proposed Options 1 and 2 in 2045 and shows the significant reductions in NO_X emissions from the proposal. In general, we estimate that Option 2 would result in lower emission reductions because of the less stringent emission standards combined with shorter useful life and warranty periods than the proposed Option 1 in MY 2031. Section VI and draft Regulatory Impact Analysis (RIA) Chapter 5 provide more information on our projected emission reductions for proposed Options 1 and 2, as well as the Alternative.

The proposed criteria pollutant program in proposed Options 1 and 2 would also reduce emissions of other pollutants. For instance, the proposed Option 1 would result in a 27 percent reduction in benzene and a 0.7 percent reduction in methane from highway heavy-duty engines in 2045. Leading up to 2045, emission reductions are expected to increase over time as the fleet turns over to new, compliant engines.

Reductions in emissions of NO_X, VOC, PM_2.5, and CO from the proposed rule are projected to lead to decreases in ambient concentrations of ozone, PM_2.5, NO₂ , and CO. The proposed Option 1 standards would significantly decrease ozone concentrations across the country, with a population-weighted average decrease of over 2 ppb in 2045. Ambient PM_2.5, NO₂ and CO concentrations are also predicted to improve in 2045 as a result of the proposed Option 1 program. The emission reductions provided by the proposed standards would be important in helping areas attain the NAAQS and prevent future nonattainment. In addition, the proposed Option 1 standards are expected to result in improvements in nitrogen deposition and visibility, but they are predicted to have relatively little impact on ambient concentrations of air toxics.

We also used our air quality data from modeling Option 1 to conduct a demographic analysis of human exposure to future air quality in scenarios with and without the proposed criteria pollutant standards in place. To compare demographic trends, we sorted 2045 baseline air quality concentrations from highest to lowest concentration and created two groups: Areas within the contiguous U.S. with the worst air quality and the rest of the country. We found that in the 2045 baseline, the number of people of color living within areas with the worst air quality is nearly double that of non-Hispanic Whites. We also found that the largest predicted improvements in both ozone and PM_2.5 are estimated to occur in areas with the worst baseline air quality, where larger numbers of people of color are projected to reside. More details on our air quality modeling and demographic analyses are included in Section VII and draft RIA Chapter 6.

Our estimates of reductions in heavy-duty engine emissions, and associated air quality impacts, are based on manufacturers adding emissions-reduction technologies in response to the proposed Options 1 or 2 criteria pollutant standards, along with making emission control components more durable in response to the longer regulatory useful life periods in the proposed Options 1 or 2. We also estimate costs to both truck owners and manufacturers attributable to the longer emission warranty for both the proposed Options 1 and 2. We estimate costs of the proposed Options 1 and 2 to both manufacturers and truck owners in our program cost analysis in Section V and draft RIA Chapter 7.

Our evaluation of costs to manufacturers includes direct costs ( i.e., cost of materials, labor costs) and indirect manufacturing costs ( e.g., warranty, research and development). The direct manufacturing costs include individual technology costs for emission-related engine components and for exhaust aftertreatment systems. Importantly, our analysis of direct manufacturing costs includes the costs of the existing emission control technologies because we expect the emissions warranty and regulatory useful life provisions in the proposed Options 1 and 2 to have some impact on not only the new technology added to comply with the proposed standards, but also on any existing emission control components. The cost estimates thus reflect the portion of baseline case engine hardware and aftertreatment systems for which new costs would be incurred due to the proposed warranty and useful life provisions, even absent any changes in the level of emission standards. The indirect manufacturing costs in our analysis include warranty costs, research and development costs, profits and other indirect costs. We combine direct and indirect manufacturing costs to calculate total technology costs, which we then add to operating costs in our calculation of program costs.

As part of our evaluation of operating costs, we estimate costs truck owners incur to repair emission control system components. Our repair cost estimates are based on industry data showing the amount spent annually by truck owners on different types of repairs, and our estimate of the percentage of those repairs that are related to emission control components. Our analysis of this data shows that extending the useful life and emission warranty periods would lower emission repair costs during several years of operation for several vehicle types. More discussion on our emission repair costs estimates of the proposed Options 1 and 2 criteria pollutant standards is included in Section V, with additional details presented in draft RIA Chapter 7.

We combined our estimates of emission repair costs with other operating costs ( i.e., urea/DEF, fuel consumption) and technology costs to calculate total program costs. Our analysis of proposed Option 1 shows that total costs for the criteria pollutant program relative to the baseline (or no action scenario) range from $1.8 billion in 2027 to $2.3 billion in 2045 (2017 dollars, undiscounted, see Table V-16). We estimate that proposed Option 2 would result in higher costs than the proposed Option 1 in 2045. We expect that the same emission control technologies would be needed to meet both the proposed Option 1 and 2 standards, which would result in the same direct technology costs in both cases. The higher projected costs of the proposed Option 2 relative to the proposed Option 1 result from our expectation that the shorter useful life and emission warranty periods of the proposed Option 2 compared to proposed Option 1 in MY 2031 and later would lead to higher emission control system repair costs for proposed Option 2 than the proposed Option 1 ( i.e., shorter emissions warranty periods result in higher emission repair costs in proposed Option 2) (see Section V for details). Overall, the analysis shows that the costs of proposed Option 1 are less than the costs of proposed Option 2. The present value of program costs for proposed Options 1 and 2, and additional details are presented in Section V.

Section VIII presents our analysis of the human health benefits associated with the proposed Options 1 and 2. We estimate that in 2045, the proposed Option 1 would result in total annual monetized ozone- and PM_2.5 -related benefits of $12 and $33 billion at a 3 percent discount rate, and $10 and $30 billion at a 7 percent discount rate. In the same calendar year, proposed Option 2 would result in total annual monetized ozone- and PM_2.5 -related benefits of $9 and $26 billion at a 3 percent discount rate, and $8 and $23 billion at a 7 percent discount. These benefits only reflect those associated with reductions in NO_X emissions (a precursor to both ozone and secondarily-formed PM_2.5) and directly-emitted PM_2.5 from highway heavy-duty engines. There are additional human health and environmental benefits associated with reductions in exposure to ambient concentrations of PM_2.5, ozone, and NO2 that EPA has not quantified due to data, resource, or methodological limitations. There would also be benefits associated with reductions in air toxic pollutant emissions that result from the proposed program, but we did not attempt to monetize those impacts due to methodological limitations. The estimated benefits of the proposed Options 1 and 2 would be larger if we were able to monetize all unquantified benefits at this time. More detailed information about the benefits analysis conducted for the proposal, including the present value of program benefits for Options 1 and 2, is included in Section VIII and draft RIA Chapter 8.

We compare total monetized health benefits to total costs associated with the proposed Options 1 and 2 in Section IX. Table 6 shows that annual benefits of the proposed Option 1 would be larger than the annual costs in 2045, with annual net benefits of $9 and $31 billion assuming a 3 percent discount rate, and net benefits of $8 and $28 billion assuming a 7 percent discount rate. Annual benefits would also be larger than annual costs in 2045 for the proposed Option 2, although net benefits would be slightly lower than from the proposed Option 1 (net benefits of proposed Option 2 would be $6 and $23 billion at a 3 percent discount rate, and net benefits of $5 and 21 billion at a 7 percent discount rate). For both the proposed Options 1 and 2, benefits also outweigh the costs when expressed in present value terms and as equalized annual values.

Section X examines the potential impacts of the proposed standards on heavy-duty vehicles (sales, mode shift, fleet turnover) and employment in the heavy-duty industry. The proposed standards may impact vehicle sales due to both changes in purchase price and longer emission warranty mileage requirements; these effects may show up as increased purchases of more new vehicles than usual before the proposed standards come into effect, in anticipation of higher prices after the proposed standards (“pre-buy”). The proposed standards may also reduce sales after the proposed standards would be in place (“low-buy”). In this proposal, we suggest an approach to quantify potential impacts on vehicle sales due to new emission standards; we also provide an example of how the results could be applied to the final regulatory analysis for this rule in draft RIA Chapter 10.1. Our example results for proposed Option 1 suggest pre- and low-buy for Class 8 trucks may range from zero to approximately two percent increase in sales over a period of up to 8 months before the 2031 standards begin (pre-buy), and a decrease in sales from zero to approximately two percent over a period of up to 12 months after the 2031 standards begin (low-buy). We have provided the example results as information for commenters to consider and provide input to EPA on this type of approach for quantifying how emissions regulations may impact heavy-duty vehicle sales fleet turnover. Based on input we receive, we may consider using this type of analysis in the final rule to inform both the potential impacts on vehicle sales, and the related impacts on employment in the heavy-duty industry. We expect little mode shift due to the proposed standards because of the large difference in cost of moving goods via trucks versus other modes of transport ( e.g., planes or barges).

Employment impacts of the proposed standards depend on the effects of the standards on sales, the share of labor in the costs of the standards, and changes in labor intensity due to the standards. We quantify the effects of costs on employment, and we discuss the effects due to sales and labor intensity qualitatively. This partial quantification of employment impacts estimates that increased costs of vehicles and parts would, by itself and holding labor intensity constant, be expected to increase employment by 400 to 2,200 job-years in 2027, and 300 to 1,800 job-years in 2032 under proposed Option 1. Employment would be expected to increase by 400 to 2,200 job years, and 300 to 1,500 job years in 2027 and 2032 respectively under proposed Option 2. See Section X for further detail on limitations and assumptions of this analysis.

Finally, the projected cost and GHG emission impacts of the proposed changes to the HD GHG Phase 2 program are described in Section XI.E.

E. Summary of Specific Requests for Comments

We are requesting comment on all aspects of this proposed rulemaking. In addition, as detailed in the sections that follow, we are specifically requesting comments from stakeholders on a variety of key topics throughout this proposed to inform the final rulemaking process. In this section we highlight topics on which we believe it would be especially beneficial to receive comments from stakeholders, or which may be of most interest to stakeholders.

Section III presents extensive information and analyses, including two options for the proposed criteria pollutant standards, to provide notice that EPA will be considering a range of numeric emission standard values and implementation dates in the final rule. We are requesting comment on the proposed Options 1 and 2, as well as the Alternative, standards for each duty cycle, as well as the one- and two-step approaches in proposed Options 1 and 2, respectively, and the implementation dates of MYs 2027 and 2031. In addition, we are requesting input on several aspects of the proposed new LLC duty cycle for heavy-duty CI engines and applying the SET duty cycle to heavy-duty SI engines (see Section III). We are also requesting comment on several aspects of the proposed off-cycle standards for heavy-duty CI engines, including the levels of the standards in proposed Options 1 and 2 and the specific operating range covered by each bin, and whether off-cycle standards and in-use testing should also apply for SI engines. For SI engines, we request comment on our proposed refueling HC emission standard for incomplete vehicles above 14,000 lb GVWR, including requests for comment and data to inform test procedure updates we should consider to measure HC emissions from these larger fuel systems and vehicles. We are also requesting comment on whether EPA should finalize interim standards for testing used to verify that the engine meets the standards through useful life ( i.e., in-use testing that occurs after the vehicle enters commerce). Typically, EPA sets the same standards for in-use testing and certification testing but, in some cases, we have provided higher in-use standards to give manufacturers time to gain experience with the new technology needed to meet the standards. As outlined in this Executive Summary and discussed in Sections III and IV, we are proposing to significantly lower NO_X emission standards and to significantly increase the regulatory useful life for heavy-duty on highway engines, which would require manufactures to develop and produce additional engine and aftertreatment technology. Due to the combination of lower (more stringent) numeric standards and longer useful periods included in our proposal, we are requesting comment on whether EPA should finalize in-use standards that are 40 to 100 percent higher than the proposed Option 1 standards for MY 2027 to MY 2033 engines.

In Section IV we detail our requests for comment on a number of topics related to our proposed lengthened useful life and warranty periods, as well as other compliance provisions and flexibilities. For instance, we are requesting stakeholder input on our proposed useful life and warranty periods, as well as the range of options covered by the proposed Options 1 and 2, or other alternatives outside of that range. In addition to the proposed warranty periods, we request comment on other approaches to warranty, such as graduated warranty phases, that may similarly ensure long-term in-use emission performance with a smaller impact on the purchase price. We further request comment on our proposed provisions to increase the likelihood that emission controls will be maintained properly through more of the service life of heavy-duty engines ( e.g., revise inducement strategies, improve serviceability). In addition, we are interested in stakeholder input on our proposed approaches for the durability demonstration that manufacturers are required to include their application for certification (see Section IV.F for details). We are also interested in stakeholder input on our proposed requirements for manufacturers choosing to generate NO_X emission credits from BEVs or FCEVs, as well as whether EPA should consider for this final rule, or other future rules, restrictions for NO_X emission credits in the longer term ( e.g., beyond MY 2031) (See Section IV.I for details).

Throughout Sections III and IV, we discuss areas where our proposal differs from the California Air Resources Board (CARB) Heavy-Duty Omnibus Rulemaking, and request comment on our proposal, including whether it is appropriate to harmonize the federal and CARB regulatory programs more in light of the authority and requirements of CAA section 202, and the benefits or challenges if EPA were to finalize particular aspects of its program that are or are not fully aligned with the Omnibus.

There are also several topics that we are requesting comment on that relate to the analyses that support our proposal. For instance, we are interested in stakeholder input on our approach for estimating emission reductions from lengthening useful life and warranty periods (see Section VI for details). We are also interested in comments on our estimate of repair costs for emission control system components (see Section V for details). We request comment on the method we outline to estimate potential impacts of a proposed regulation on heavy-duty vehicle sales; we also request comment on approaches to estimate employment impacts attributable to the proposed rule (see Section X for details).

We are also interested in input from environmental justice stakeholders and underserved and overburdened communities, including children's health stakeholders, regarding the need for revised standards and how heavy-duty vehicles affect communities (see Section II); the air quality improvements we project from this proposal and how they are distributed (see Section VII); and ways the proposal could be improved to advance environmental protection for all people, including people of color, low-income communities, and those who live near highways or in heavily trafficked areas with frequent truck congestion and idling, such as ports.

In Section XI, we request comment in a number of areas related to the proposed updates to the HD GHG Phase 2 program for certain heavy-duty vehicles that are shifting to zero-emission vehicles. We are considering whether it would be appropriate in the final rule to increase the stringency of the standards even more than what we propose. Therefore, we request information on heavy-duty electric vehicle sales projections, including for what HD vehicle types, to help inform our HD electric vehicle sales projections in the MY 2024 through MY 2029 timeframe. We also are considering whether to establish more stringent standards beyond MY 2027, specifically in MY 2028 and MY 2029 using the methodology described in Section XI.C.1. We request comment on appropriate stringency and supporting data for each of those model years.

We are also interested in stakeholder input that supports changes to the advanced technology credit multiplier approach under consideration. In addition, we request comment under this proposal on how EPA can best consider the potential for ZEV technology to significantly reduce air pollution from the heavy-duty vehicle sector, including whether and how to consider including specific sales requirements for HD ZEVs.

For these and all requests for comment detailed throughout the proposal, stakeholders are encouraged to provide their rationale and any available data that supports to their perspectives.

I. Introduction

A. Brief Overview of the Heavy-Duty Truck Industry

Heavy-duty highway vehicles (also referred to as “trucks” in this preamble) range from commercial pickup trucks to vocational vehicles that support local and regional transportation, construction, refuse collection, and delivery work, to line-haul tractor-trailers that move freight cross-country. This diverse array of vehicles is categorized into weight classes based on gross vehicle weight ratings (GVWR). These weight classes span Class 2b pickup trucks and vans from 8,500 to 10,000 lbs GVWR through Class 8 line-haul tractors and other commercial vehicles that exceed 33,000 lbs GVWR.

Heavy-duty highway vehicles are primarily powered by diesel-fueled, compression-ignition (CI) engines. However, gasoline-fueled, spark-ignition (SI) engines are common in the lighter weight classes, and smaller numbers of alternative fuel engines ( e.g., liquified petroleum gas, compressed natural gas) are found in the heavy-duty fleet. Vehicles powered by electricity, either in the form of battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs) are also increasingly entering the heavy-duty fleet. The operational characteristics of some commercial applications ( e.g., delivery vehicles) can be similar across several vehicle weight classes, allowing a single engine, or electric power source in the case of BEVs and FCEVs, to be installed in a variety of vehicles. For instance, engine specifications needed for a Class 4 parcel delivery vehicle may be similar to the needs of a Class 5 mixed freight delivery vehicle or a Class 6 beverage truck. Any performance differences needed to operate across this range of vehicles can be achieved through adjustments to chassis-based systems ( i.e., transmission, cooling system) external to the engine.

The industry that designs and manufactures these heavy-duty vehicles is composed of three primary segments: Vehicle manufacturers, engine manufacturers and other major component manufacturers, and secondary manufacturers ( i.e., body builders). Some vehicle manufacturers are vertically integrated, designing, developing, and testing their engines in-house for use in their vehicles, while others purchase some or all of their engines from independent engine suppliers. Today, only one major independent engine manufacturer supports the heavy-duty truck industry, though some vehicle manufactures sell their engines or “incomplete vehicles” ( i.e., chassis that include their engines, the frame, and a transmission) to body builders who design and assemble the final vehicle. Each of these subindustries is often supported by common suppliers for subsystems such as transmissions, axles, engine controls, and emission controls.

In addition to the manufacturers and suppliers responsible for producing highway heavy-duty vehicles, an extended network of dealerships, repair and service facilities, and rebuilding facilities contribute to the sale, maintenance, and extended life of these vehicles and engines. Heavy-duty vehicle dealerships offer customers a place to order vehicles from a specific manufacturer and include service facilities for those vehicles and engines. Dealership service technicians are trained to perform regular maintenance and make repairs, which generally include repairs under warranty and in response to manufacturer recalls. Some trucking fleets, businesses, and large municipalities benefit from hiring their own technicians to service their vehicles in their own facilities. Many refueling centers along major trucking routes have also expanded their facilities to include roadside assistance and service stations to diagnose and repair common problems.

Heavy-duty CI engines installed in the larger weight classes of vehicles are designed to be rebuilt. Dealerships and other service facilities are generally equipped to replace common components, such as pistons and bearings that wear over time. However, large-scale ( i.e., “out-of-frame”) engine overhauls that replace most of the engine components require a more sophisticated process that only a limited number of facilities provide. Some heavy-duty engine manufacturers have established their own rebuilding facilities as a separate branch of their operations and others work with independent rebuilding factories that are affiliated with multiple engine manufacturers. Rebuilding allows owners to extend the life of their engines at a lower cost than purchasing a replacement vehicle, which has made the practice common for some heavy-duty engines.

The end-users for highway heavy-duty vehicles are as diverse as the applications for which these vehicles are purchased. Smaller weight class heavy-duty vehicles are commonly purchased by delivery services, contractors, and municipalities. The middle weight class vehicles tend to be commercial vehicles for businesses and municipal work that transport people and goods locally and regionally or provide services such as utilities. Vehicles in the heaviest weight classes are generally purchased by businesses with high load demands, such as construction, towing or refuse collection, or freight delivery fleets and owner-operators with both load and speed demands for regional and long-haul goods movement. The competitive nature of the businesses and owner-operators that purchase and operate highway heavy-duty vehicles means that any time the vehicle is unable to operate due to maintenance or repair ( i.e., downtime) can lead to a loss in income. This need for reliability drives much of the truck and engine manufacturers' innovation and research to meet the needs of their customers.

B. History of Emission Standards for Heavy-Duty Engines and Vehicles

Emission standards for heavy-duty highway engines in the U.S. were first issued by the Department of Health, Education, and Welfare in the 1960s. These standards and the corresponding certification and testing procedures were codified at 45 CFR part 1201. In 1972, shortly after EPA was created as a federal agency and given responsibility for regulating heavy-duty engines, EPA published new standards and updated procedures while migrating the regulations to 40 CFR part 85 as part of the effort to consolidate all EPA regulations in a single location. EPA created 40 CFR part 86 in 1976 to reorganize emission standards and certification requirements for light-duty vehicles and heavy-duty highway engines. In 1985, EPA promulgated new standards for heavy-duty highway engines, codifying the standards in 40 CFR part 86, subpart A. Since then, EPA has promulgated several rules for highway heavy-duty engines and vehicles to set new and more stringent emission standards for criteria pollutants and precursors, to set requirements for controlling evaporative and refueling emissions, to establish emission control programs for greenhouse gases (GHGs), and to add or revise certification procedures.

EPA's criteria pollutant regulatory programs for the heavy-duty highway industry apply to engines. Our regulations require that engine manufacturers identify the “primary intended service class” for each engine by considering the vehicles for which they design and market their engines. Heavy-duty CI engines are specified as light heavy-duty engine (Light HDE), medium heavy-duty engine (Medium HDE), or heavy heavy-duty engine (Heavy HDE) based largely on the weight class of the vehicles in which the engines are expected to be installed and the potential for rebuild. SI heavy-duty engines are generally specified as a single spark-ignition HDE service class unless they are designed or intended for use in the largest heavy-duty vehicles, and therefore considered heavy HDEs. EPA sets emission standards and other regulatory provisions, including regulatory useful life and emissions warranty periods, that are targeted for the operational characteristics of each primary intended service class.

In the 1990s, EPA issued increasingly stringent standards for NO_X, CO, HC, and PM. These exhaust standards were derived from engine-based emission control strategies and manufacturers generally certified their engines' emission performance over defined duty cycles on an engine dynamometer ( i.e., “engine certification”). In 1997, EPA finalized standards for heavy-duty highway diesels (62 FR 54693, October 21, 1997), effective beginning with the 2004 model year, including a combined non-methane hydrocarbon (NMHC) and NO_X standard that represented a reduction of NO_X emissions by 50 percent. These NO_X reductions also resulted in significant reductions in secondary nitrate PM.

In early 2001, EPA finalized the 2007 Heavy-Duty Engine and Vehicle Rule (66 FR 5002, January 18, 2001) to continue addressing NO_X and PM emissions from both diesel and gasoline-fueled highway heavy-duty engines. This rule established a comprehensive national program that regulated a heavy-duty engine and its fuel as a single system, with emission standards taking effect beginning with model year (MY) 2007 and fully phasing in by MY 2010 (EPA 2010 standards). Prior to 2007, emission standards were based on controlling the emissions formed during the combustion process ( i.e., engine-out emissions), and there was no further control of emissions between the engine and the truck's tailpipe. But with promulgation of the 2007 final rule, emission standards were, for the first time, based on the use of technologies to capture, convert, and reduce harmful engine-out emissions, resulting in tailpipe emissions that were cleaner than engine-out emissions. By and large, the industry met these new standards through the use of exhaust aftertreatment technologies, namely, diesel oxidation catalysts, particulate filters, and high-efficiency catalytic exhaust emission control devices. Consistent with previous criteria pollutant regulatory programs, the program also offered flexibility to manufacturers through the use of various emission credits averaging, banking, and trading (ABT) programs.

To ensure proper functioning of these aftertreatment technologies, which could be damaged by sulfur, EPA also reduced the allowable level of sulfur in highway diesel fuel by 97 percent by mid-2006. Together, the use of exhaust aftertreatment technologies and lower-sulfur fuel resulted in diesel-fueled trucks that emitted PM and NO_X tailpipe emissions at levels 90 percent and 95 percent below emission levels from then-current highway heavy-duty engines, respectively. The PM standard for new highway heavy-duty engines was set at 0.01 grams (10 milligrams, or 10 mg) per horsepower-hour (mg/hp-hr) by MY 2007 and the NO_X and NMHC standards of 200 mg/hp-hr and 140 mg/hp-hr, respectively, were set to phase in between model years 2007 and 2010. In finalizing that rule, EPA estimated that the emission reductions would achieve significant health and environmental impacts, and that the total monetized PM_2.5 and ozone-related benefits of the program would exceed $70 billion, versus program costs of $4 billion (1999$).

In 2005, EPA finalized a manufacturer-run, in-use testing program that uses portable emission measurement systems to measure HC, CO, NO_X, and PM emissions from the exhaust of in-use heavy-duty diesel trucks (70 FR 34594, June 14, 2005). The fully enforceable program began in 2007. This effort was a significant advancement in helping to ensure that the benefits of more stringent emission standards are realized under real-world driving conditions.

In 2009, as advanced emissions control systems were being introduced to meet the MY 2007/2010 standards, EPA promulgated a final rule to require that these advanced emissions control systems be monitored for malfunctions via an onboard diagnostic (OBD) system (74 FR 8310, February 24, 2009). The rule, which has been fully phased in, required engine manufacturers to install OBD systems that monitor the functioning of emission control components on new engines and alert the vehicle operator to any detected need for emission-related repair. It also required that manufacturers make available to the service and repair industry information necessary to perform repair and maintenance service on OBD systems and other emission related engine components. In addition, EPA published a series of documents that provided guidance to manufacturers on potential methods and measures to ensure that trucks equipped with Selective Catalytic Reduction (SCR) technology would be refilled with the specified quantity and quality of a urea-water mixture (also known as diesel exhaust fluid, or DEF) necessary for the proper functioning of this NO_X -reducing technology. These guidance documents describe potential approaches that included progressive levels of alerts and warnings communicated to the driver of the truck, which would allow adequate time to refill the DEF tank, but ultimately, if DEF is not added, or if it is determined to be of insufficient quality, a vehicle speed-limiting “inducement” would be triggered, requiring the DEF tank to be refilled or the system to be repaired.

Also in 2009, EPA and Department of Transportation's National Highway Traffic Safety Administration (NHTSA) began working on a joint regulatory program to reduce GHG emissions and fuel consumption from heavy-duty vehicles and engines. By utilizing regulatory approaches recommended by the National Academy of Sciences, the first phase (“Phase 1”) of the GHG and fuel efficiency program was finalized in 2011 (76 FR 57106, September 15, 2011). The Phase 1 program, spanning implementation from MY 2014 to 2018, included separate standards for highway heavy-duty vehicles and heavy-duty engines. The program offered flexibility allowing manufacturers to attain these standards through a mix of technologies and the option to participate in an emissions credit ABT program. In the Phase 1 rulemaking EPA also revised the heavy-duty vehicle and engine regulations to make them consistent with the light-duty vehicle approach, such that all criteria pollutant and GHG standards would apply regardless of fuel type, including all-electric vehicles (EVs).

In 2016, EPA and NHTSA finalized the Heavy-Duty Phase 2 GHG and fuel efficiency program (“HD GHG Phase 2”) (81 FR 73478, October 25, 2016). HD GHG Phase 2 includes technology-advancing performance-based standards for highway heavy-duty vehicles and heavy-duty engines that will phase in over the long term, with initial standards for most vehicles and engines commencing in MY 2021, increasing in stringency in MY 2024, and culminating in MY 2027 standards. HD GHG Phase 2 built upon the Phase 1 program and set standards based not only on currently available technologies, but also on technologies that were still under development or not yet widely deployed. To ensure adequate time for technology development, HD GHG Phase 2 provided up to 10 years lead time to allow for the development and phase-in of these control technologies. EPA recently finalized technical amendments to the HD GHG Phase 2 rulemaking (“HD Technical Amendments”) that included changes to the test procedures for heavy-duty engines and vehicles to improve accuracy and reduce testing burden.

C. Petitions to EPA for Additional NO_X Emissions Control

In the summer of 2016 more than 20 organizations, including state and local air agencies from across the country, petitioned EPA to develop more stringent NO_X emission standards for on-road heavy-duty engines. Among the reasons stated by the petitioners for such an EPA rulemaking was the need for NO_X emission reductions to reduce adverse health and welfare impacts and to help areas attain the NAAQS. EPA subsequently met with a wide range of stakeholders in listening sessions, during which certain themes were consistent across those stakeholders. For example, it became clear that there is broad support for federal action in collaboration with the California Air Resources Board (CARB). So-called “50-state” standards would enable technology suppliers and manufacturers to efficiently produce a single set of reliable and compliant products. There was also broad acknowledgement of the value of aligning implementation of new NO_X standards with existing MY 2021, 2024, and 2027 milestones for HD Phase 2 GHG and fuel efficiency standards. Stakeholders thought that such alignment would ensure that the GHG and fuel consumption reductions achieved under HD GHG Phase 2 are maintained and allow the regulated industry to implement GHG- and NO_X -reducing technologies into their products at the same time.

EPA responded to the petitions on December 20, 2016, noting that an opportunity exists to develop a new, harmonized national NO_X reduction strategy for heavy-duty highway engines. EPA emphasized the importance of scientific and technological information when determining the appropriate level and form of a future low NO_X standard and highlighted the following potential components of the action:

• Lower NO_X emission standards

• Improvements to test procedures and test cycles to ensure emission reductions occur in the real world, not only over the currently applicable certification test cycles
• Updated certification and in-use testing protocols
• Longer periods of mandatory emission-related component warranties
• Consideration of longer regulatory useful life, reflecting actual in-use activity
• Consideration of rebuilding
• Incentives to encourage the transition to current- and next-generation cleaner technologies as soon as possible

As outlined in the Executive Summary and detailed in the sections that follow, this proposed rulemaking considered these components.

D. California Heavy-Duty Highway Low NO_X Program Development

In this section, we present a summary of recent efforts by the state of California to establish new, lower emission standards for highway heavy-duty engines and vehicles. For the past several decades, EPA and the California Air Resources Board (CARB) have worked together to reduce air pollutants from highway heavy-duty engines and vehicles by establishing harmonized emission standards for new engines and vehicles. For much of this time, EPA has taken the lead in establishing emission standards through notice and comment rulemaking, after which CARB would adopt the same standards and test procedures. For example, EPA promulgated the current heavy-duty engine NO_X and PM standards in a 2001 final rule, and CARB subsequently adopted the same emission standards. EPA and CARB often cooperate during the implementation of highway heavy-duty standards. Thus, for many years, the regulated industry has been able to design a single product line of engines and vehicles that can be certified to both EPA and CARB emission standards (which have been the same) and sold in all 50 states.

Given the significant ozone and PM air quality challenges in the state of California, CARB has taken several steps since the EPA 2010 standards were implemented to encourage or establish standards and requirements that go beyond EPA requirements, to further reduce NO_X emissions from heavy-duty vehicles and engines in its state. CARB's optional (voluntary) low NO_X program, which started in 2013, was created to encourage heavy-duty engine manufacturers to introduce technologies that emit NO_X at levels below the current EPA 2010 standards. Under this optional program, manufacturers can certify engines to one of three levels of stringency that are 50, 75, and 90 percent below the existing EPA 2010 standards with the lowest optional standard being 20 milligrams NO_X per horsepower-hour (mg/hp-h). To date, only natural gas and liquefied petroleum gas engines have been certified to these optional standards.

In May 2016, CARB published its Mobile Source Strategy that outlined its approach to reduce in-state emissions from mobile sources and meet its air quality targets. In November 2016, CARB held its first Public Workshop on its plans to update its heavy-duty engine and vehicle programs. CARB's 2016 Workshop kicked off a technology demonstration program (the CARB “Low NO_X Demonstration Program”), and announced plans to update emission standards, laboratory-based and in-use test procedures, emissions warranty, durability demonstration requirements, and regulatory useful life provisions. The initiatives introduced in its 2016 Workshop have since become components of CARB's Heavy-Duty “Omnibus” Rulemaking.

CARB's goal for its Low NO_X Demonstration Program was to investigate the feasibility of reducing NO_X emissions to levels significantly below today's EPA 2010 standards. Southwest Research Institute (SwRI) was contracted to perform the work, which was split into three “Stages.” In Stage 1 and 1b, SwRI demonstrated an engine technology package capable of achieving a 90 percent NO_X emissions reduction on today's regulatory test cycles to a useful life of 435,000 miles using an accelerated aging process. In Stage 2, SwRI developed and evaluated a new low load-focused engine test cycle. In Stage 3, SwRI evaluated a new engine platform and different technology package to ensure both criteria and GHG emission performance. EPA has been closely observing CARB's Low NO_X Demonstration Program as a member of the Low NO_X Advisory Group for the technology development work, which includes representatives from heavy-duty engine and aftertreatment industries, as well as from federal, state, and local governmental agencies.

CARB has published several updates related to its Omnibus Rulemaking. In June 2018, CARB approved its “Step 1” update to California's emission control system warranty regulations. Starting in MY 2022, the existing 100,000-mile warranty for all diesel engines will increase to 110,000 miles for engines certified as light heavy-duty, 150,000 miles for medium heavy-duty engines, and 350,000 miles for heavy heavy-duty engines. In November 2018, CARB approved revisions to the OBD requirements that include implementation of real emissions assessment logging (REAL) for heavy-duty engines and other vehicles. In April 2019, CARB published a “Staff White Paper” to present its staff's assessment of the technologies they believed were feasible for medium and heavy heavy-duty diesel engines in the 2022-2026 timeframe.

In August 2020, the CARB governing board approved the staff proposal for the Omnibus rule and directed staff to initiate the process of finalizing the provisions. The final Omnibus rule was approved by the California Office of Administrative Law in December 2021. The final rule includes updates to CARB engine standards, duty-cycle test procedures, and heavy-duty off-cycle testing program that would take effect in MY 2024, with additional updates to warranty, durability, and useful life requirements and further reductions in standards in MYs 2027 and 2031.

As described in Sections I.F and I.G, with details in Sections III and IV, EPA is proposing new NO_X , PM, HC, and CO emission standards for heavy-duty engines that reflect the greatest degree of emission reduction achievable through the application of technology that we have determined would be available for the model years to which the proposed standards would apply. In doing so we have given appropriate consideration to additional factors, namely lead time, cost, energy, and safety (see Sections I.F and I.G for more discussion). Throughout the rulemaking process we will continue to evaluate what standards are appropriate given the factors that we are directed to consider under CAA section 202(a)(3). As noted at the start of this Section I.D, EPA and CARB have historically worked together to establish harmonized emission standards for new heavy-duty engines and vehicles. We have received comments from different stakeholder groups who have expressed perspectives on the alignment between the EPA and CARB Omnibus standards they would like EPA to consider during the rulemaking. For instance, in response to an Advance Notice of Proposed Rulemaking (ANPR) for this rule, many stakeholders encouraged EPA to develop a national program harmonized to the greatest extent possible (see Section I.E). Following the ANPR, various stakeholders have provided EPA with additional perspectives on the Omnibus rule and on the extent to which EPA should align with the California program. For example, organizations such as the National Association of Clean Air Agencies, the National Tribal Air Association, as well as multiple vehicle supplier trade associations have written letters to EPA in support of strong federal standards that reflect both the stringency and timeline of CARB's standards. In contrast, some engine manufacturers have raised concerns about EPA harmonizing its national program with California's rule because of their concerns with that program's overall stringency, costs, and focus on near-term NO_X reductions over long-term CO₂ emission reductions. EPA has considered these harmonization comments in light of the authority and requirements of CAA sections 202 and 207 in developing the proposed standards, regulatory useful life periods, and emissions warranty periods and intends to continue to take into consideration potential harmonization with the CARB Omnibus program, as appropriate and consistent with CAA sections 202 and 207, during the rulemaking. As described in Sections III and IV, a notable difference between the proposed EPA program and the Omnibus rule is that the first step of the Omnibus rule takes effect in MY 2024, whereas the first step of the proposed EPA program is in MY 2027. EPA's statutory authority requires a four-year lead time for any heavy-duty engine or vehicle standard promulgated or revised under CAA section 202(a)(3) (see Section I.F). In Sections III and IV, we discuss areas where our proposal aligns with or differs from the Omnibus rule and request comment on issues related to harmonization between the federal and CARB regulatory programs, including benefits or challenges if EPA were to finalize particular aspects of its program that are not fully aligned with the Omnibus rule.

As discussed in the draft RIA, we analyzed the emission inventory and air quality impacts for the proposed criteria pollutant standards before the Omnibus Rule was finalized. We may incorporate the Omnibus rule into our emission inventory and other analyses as appropriate for the final rulemaking (FRM). We also may incorporate the CARB Advanced Clean Truck (ACT) Regulation into our final rule analyses. As further discussed in Sections IV, VI, and XI, the CARB ACT Regulation requires a minimum percentage of each manufacturer's heavy-duty vehicle sales in the state of California to be zero tailpipe emission technologies starting in MY 2024.

E. Advance Notice of Proposed Rulemaking

The ANPR provided background for the provisions proposed in this rulemaking to address criteria pollutant emissions from heavy-duty engines, including technologies we are evaluating, test programs we have initiated, and compliance programs under consideration, as well as requests for comments and data. The ANPR did not include discussion on the potential stringency of standards, potential costs of the standards, or a quantitative assessment of societal impacts ( e.g., air quality, economic, environmental health); these topics are presented in this proposal.

EPA received over 300 comments on the ANPR from a wide range of stakeholders, including: Government organizations (state, local, and Tribal), environmental groups, trade associations, heavy-duty engine manufacturers, independent owner-operators, suppliers, individual fleets, and individual private citizens. We provide a brief overview of the perspectives included in these comments in this subsection, with more specific discussion of comments included in subsequent sections of the proposal as relevant to individual comments or groups of comments.

Comments from government organizations, including multiple state and local air agencies, emphasized that reductions in NO_X emissions from heavy-duty engines are necessary for attainment and maintenance of the NAAQS. States commented that they cannot control heavy-duty engine emissions since they cross state borders and controlling emissions from other sources would be economically burdensome. Commenters stated that areas in nonattainment of the NAAQS are having difficulty attaining, and some areas currently in attainment are close to or exceeding the NAAQS. As further discussed in Section II, commenters noted environmental justice and other public health concerns, along with regional haze and ecosystem concerns. These commenters requested stringent emission controls on heavy-duty engines in as short a timeframe as possible (including early incentives) and expressed widespread interest in ensuring control over the lifetime of the engine, including addressing emissions from tampering and idling.

Several environmental groups submitted comments that were similar to several of the state and local agency comments; environmental groups supported stringent emission controls and maintaining that level of emission control for longer durations by lengthening useful life and emission warranty periods. These commenters further supported improvements to the in-use testing program for heavy-duty diesel engines, and anti-tampering measures for all heavy-duty engines.

Comments from the Truck and Engine Manufacturers Association (EMA), a trade association for heavy-duty engine and truck manufacturers emphasized broad support for a 50-state program and encouraged EPA to conduct a thorough analysis of the costs and benefits of proposed NO_X emission standards. To emphasize their cost concerns, EMA provided an industry-sponsored assessment of the cost to comply with potential requirements discussed in the April 2019 CARB Staff Whitepaper.

Several truck owners, truck operators, fleets, and dealerships also expressed general support for a national, harmonized low-NO_X program. Many commenters included their experiences with expensive towing costs and downtime from emission system failures; they stated that although the reliability of emission system controls has improved since the 2010 timeframe, it remains an ongoing concern. ANPR commenters also indicated that engine derates or “inducements” are a significant source of operator frustration. In addition, commenters urged EPA to conduct a thorough cost assessment, and noted that if the initial purchase price, or operational costs for new trucks is too high, then it may incentivize owners to keep older trucks on the road. These commenters expressed varying views on lengthening emission warranty requirements, with some urging a careful consideration of the impacts of longer warranty requirements, while others expressed support for longer warranty requirements.

Suppliers, supplier trade groups, and labor groups were all generally supportive of more stringent NO_X emission standards. They also generally stated strong support for a 50-state, harmonized EPA-CARB program. They also emphasized the importance of providing industry with regulatory certainty. They noted that EPA must balance emission reductions with technology costs, feasibility, lead-time, and avoid market disruptions. Several suppliers and trade groups provided detailed technical information on low NO_X technology. They also expressed support for longer useful life and warranty requirements but cautioned EPA to carefully design longer emissions warranty requirements and to consider a phase-in approach. Several suppliers and trade groups also supported incentives for the early introduction of low-NO_X technology.

All of the ANPR comments are part of the docket for the proposal and have informed our thinking in developing the proposed provisions to address criteria pollutant emissions from heavy-duty engines.

F. EPA Statutory Authority for the Proposal

This section briefly summarizes the statutory authority for the proposed rule. Title II of the Clean Air Act provides for comprehensive regulation of mobile sources, authorizing EPA to regulate emissions of air pollutants from all mobile source categories. Specific Title II authorities for this proposal include: CAA sections 202, 203, 206, 207, 208, 213, 216, and 301 (42 U.S.C. 7521, 7522, 7525, 7541, 7542, 7547, 7550, and 7601). We discuss some key aspects of these sections in relation to this proposed action immediately below (see also Section XIV of this preamble), as well as in each of the relevant sections later in this proposal. Regarding the confidentiality determinations EPA is proposing to make through this notice and comment rulemaking for much of the information collected by EPA for certification and compliance under Title II, see Section XII.A. for discussion of relevant statutory authority.

Statutory authority for the proposed NO_X, PM, HC, CO, and GHG emission standards in this action comes from CAA section 202(a) which states that “the Administrator shall by regulation prescribe (and from time to time revise) . . . standards applicable to the emission of any air pollutant from any class or classes of new . . . motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Standards under CAA section 202(a) take effect “after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.” Thus, in establishing or revising CAA section 202(a) standards designed to reduce air pollution that endangers public health and welfare, EPA also must consider issues of technological feasibility, compliance cost, and lead time. EPA may consider other factors and in previous engine and vehicle standards rulemakings has considered the impacts of potential standards on the heavy-duty industry, fuel savings, oil conservation, energy security and other energy impacts, as well as other relevant considerations such as safety.

1. Statutory Authority for Proposed Criteria Pollutant Program

Section 202(a)(3) further addresses EPA authority to establish standards for emissions of NO_X, PM, HC, and CO from heavy-duty engines and vehicles. Section 202(a)(3)(A) requires that such standards “reflect the greatest degree of emission reduction achievable through the application of technology which the Administrator determines will be available for the model year to which such standards apply, giving appropriate consideration to cost, energy, and safety factors associated with the application of such technology.” Section 202(a)(3)(B) allows EPA to take into account air quality information in revising such standards. Section 202(a)(3)(C) provides that standards shall apply for a period of no less than three model years beginning no earlier than the model year commencing four years after promulgation. CAA section 202(a)(3)(A) is a technology-forcing provision and reflects Congress' intent that standards be based on projections of future advances in pollution control capability, considering costs and other statutory factors. CAA section 202(a)(3) neither requires that EPA consider all the statutory factors equally nor mandates a specific method of cost-analysis; rather EPA has discretion in determining the appropriate consideration to give such factors.

Section II, and Chapter 4 of the draft RIA, describe EPA's analysis of information regarding heavy-duty engines' contribution to air pollution and how that pollution adversely impacts public health and welfare. Section I.G, with more detail in Section III and Chapter 4 of the draft RIA, discusses our feasibility analysis of the standards and useful life periods for both proposed Options. Our evaluation shows that the standards and useful life periods in both steps of proposed Option 1 are feasible and would result in the greatest emission reductions achievable for the model years to which they are proposed to apply, pursuant to CAA section 202(a)(3), giving appropriate consideration to costs, lead time, and other factors. Our analysis further shows that the standards and useful life periods in proposed Option 2 are feasible in the 2027 model year, but would result in lower levels of emission reductions compared to proposed Option 1. As explained further in Section III and Chapter 3 of the draft RIA, we expect that additional data from EPA's ongoing work to demonstrate the performance of emission control technologies, as well as information received in public comments, will allow us to refine our assessments and consideration of the feasibility of the combination of the standards and useful life periods, particularly for the largest CI engines (HHDEs), in proposed Options 1 and 2, after consideration of lead time, costs, and other factors. Therefore, we are co-proposing Options 1 and 2 standards and useful life periods, and the range of options in between them, as the options that may potentially be appropriate to finalize pursuant to CAA section 202(a)(3) once EPA has considered that additional data and other information. We considered costs and lead time in designing the proposed program options, including in our analysis of how manufacturers would adopt advanced emission control technologies to meet the proposed standards for the applicable model years. For example, the first step of proposed Option 1 allows manufacturers to minimize costs by implementing a single redesign of heavy-duty engines for MY 2027, which is when both the final step of the HD GHG Phase 2 standards and the first step of the proposed Option 1 standards would start to apply. The second step of proposed Option 1 (MY 2031) would provide manufacturers the time needed to ensure that emission control components are durable enough for the proposed second step of revised standards and longer useful life periods.

As described in Section III, we are proposing new test cycles for both pre-production and post-certification testing. Manufacturers demonstrate compliance over specified duty cycle test procedures during pre-production testing, which is conducted by EPA or the manufacturer. These data and other information submitted by the manufacturer as part of their certification application are the basis on which EPA issues certificates of conformity pursuant to CAA section 206. Under CAA section 203, sales of new vehicles are prohibited unless the vehicle is covered by a certificate of conformity. Compliance with standards is required not only at certification but throughout the useful life period of the engine and vehicle, based on post-certification testing. Post-certification testing can include both specific duty cycle test procedures and off-cycle test procedures that are conducted with undefined duty cycles either on the road or in the laboratory (see Sections III.A and IV.K for more discussion on for testing at various stages in the life of an engine).

As described in Section IV, we are proposing to lengthen regulatory useful life and emission warranty periods to better reflect the mileages and time periods over which heavy-duty engines are driven today. CAA section 202(d) directs EPA to prescribe regulations under which the useful life of vehicles and engines are determined and establishes minimum values of 10 years or 100,000 miles, whichever occurs first, unless EPA determines that a period of greater duration or mileage is appropriate. EPA may apply adjustment factors to assure compliance with requirements in use throughout useful life (CAA section 206(a)). CAA section 207(a) requires manufacturers to provide an emissions warranty, which EPA last updated in its regulations for heavy-duty engines in 1983 (see 40 CFR 86.085-2).

2. Statutory Authority for Targeted Revisions to the Heavy-Duty GHG Phase 2 Program

In addition, as discussed in Section XI, EPA is proposing a limited set of revisions to MY 2027 Phase 2 GHG emissions standards under its CAA section 202(a) authority described in this section (Section I.F). We have developed an approach to propose targeted updates to HD GHG Phase 2 standards that take into consideration the growing HD electric vehicle market without fundamentally changing the HD GHG Phase 2 program as a whole. In addition, we are requesting comment on potential changes to the advanced technology incentive program for electric vehicles beginning in MY 2024.

G. Basis of the Proposed Standards

Our approach to further reduce air pollution from highway heavy-duty engines and vehicles through the proposed program features several key provisions. The primary provisions address criteria pollutant emissions from heavy-duty engines. In addition, this proposal would make targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program, proposing that further GHG reductions in the MY 2027 timeframe are appropriate considering lead time, costs, and other factors, including market shifts to zero-emission technologies in certain segments of the heavy-duty vehicle sector.

1. Basis of the Proposed Criteria Pollutant Standards

Heavy-duty engines across the U.S. emit NO_X, PM, VOCs, and CO that contribute to ambient levels of ozone, PM, NO_X, and CO; these pollutants are linked to premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. In addition, these pollutants reduce visibility and negatively impact ecosystems. Data show that NO_X emissions from heavy-duty engines are important contributors to concentrations of ozone and PM_2.5 and their resulting threat to public health. As discussed in Section II, we estimate that heavy-duty engines will continue to be one of the largest contributors to mobile source NO_X emissions nationwide in the future, representing 32 percent of the mobile source and 89 percent of the onroad NO_X emission inventories in calendar year 2045. For the reasons summarized here and explained further in those sections, EPA concludes that revised standards are warranted to address the emissions of these pollutants and their contribution to national air pollution.

As required by CAA section 202(a)(3), EPA is proposing new NO_X , PM, HC, and CO emission standards for heavy-duty engines that reflect the greatest degree of emission reduction achievable through the application of technology that we have determined would be available for the model years to which the proposed standards would apply. In doing so we have given appropriate consideration to additional factors, namely lead time, cost, energy, and safety. Our technical assessments are primarily based on results from diesel engine demonstration testing conducted by CARB at Southwest Research Institute, heavy-duty gasoline and diesel engines testing conducted at EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL), heavy-duty engine certification data submitted to EPA by manufacturers, ANPR comments, and other data submitted by industry stakeholders or studies conducted by EPA, as more specifically identified in the sections that follow. We expect that additional data from EPA's ongoing work to demonstrate the performance of emission control technologies will allow us to refine our assessments and consideration of the feasibility of the combination of standards and useful life periods in proposed Options 1 and 2, after consideration of lead time, costs, and other factors. Therefore, we are co-proposing Options 1 and 2 to illustrate a broader range of potential options. We also present an alternative (the Alternative) that we considered in the development of this proposal but for which we currently lack information to conclude would be feasible throughout the useful periods included in this alternative and in the model year in which the standards would begin. As outlined in this section and detailed in Sections III and IV, we solicit comment on the proposed Options 1 and 2, the Alternative presented, or other alternatives within and outside the range of options.

As noted in the Executive Summary and discussed in Section III, the proposed Options 1 and 2 standards and the Alternative would each begin to apply in MY 2027. We selected this model year for two reasons. First, as explained in Section I.F, the CAA requires EPA to provide at least four years of lead time from the promulgation of a final rule. We expect to finalize this rulemaking in 2022, such that MY 2027 would be the earliest model year the new requirements could apply. Second, the timing of the final stage of the HD GHG Phase 2 program in MY 2027 leads us to believe that MY 2027 is the appropriate time for the proposed standards to begin since this would allow manufacturers to design a single engine platform that complies with both HD GHG Phase 2 and the criteria pollutant requirements. We expect that a single engine design for both rulemakings would minimize costs and improve reliability of the emission control components by integrating design changes for both rules (see Section III.A for more discussion on MY 2027 as the first implementation year for the proposed program).

The MY 2031 standards in proposed Option 1 would begin four model years after the MY 2027 standards in proposed Option 1, which is an additional year beyond the CAA requirement for at least three years of stability. Both steps of the proposed Option 1 standards reflect the greatest degree of emission reductions achievable in each model year when combined with the proposed longer useful life periods, new test cycles, and other compliance provisions that start in each model year. We expect that the changes to useful life in proposed Options 1 and 2 would improve component durability, but additional increases in useful life, such as those associated with the proposed MY 2031 standards in proposed Option 1, may take manufacturers more time to develop (see Section IV for more discussion). Therefore, proposed Option 1 includes a two-step approach to allow additional lead time for manufacturers to develop emission control components durable enough for the proposed longer useful life periods. In Section III.A we request comment on the two-step approach in proposed Option 1.

In Sections III and IV, we present the details of the two-step proposed Option 1 (MYs 2027 and 2031) and the proposed Option 2 that would occur in a single step (MY 2027). We also present details of the Alternative, which would also occur in a single step (MY 2027). Overall, proposed Option 2 is less stringent than the MY 2031 standards in proposed Option 1 due to higher numeric levels of the NO_X emission standards and shorter useful life periods in proposed Option 2. For our proposed Options 1 and 2 standards, we project that the emission control technologies used in MY 2027 would build on those used in light- and heavy-duty engines today. For heavy-duty CI engines, under both the proposed Option 1 MY 2031 standards and the proposed Option 2 standards, we project the use of the valvetrain engine technology combined with updates to the SCR system configuration that builds on what is used in current light-duty trucks and heavy-duty engines. For heavy-duty SI engines, the technologies we are evaluating that would achieve the standards in the proposed Options 1 and 2 largely build on the three-way catalyst-based emission control strategies used in heavy-duty SI chassis certified engine products.

The Alternative we considered includes lower (more stringent) numeric NO_X emission levels for Heavy HDEs, and lower HC emission levels for all CI and SI engine classes, combined with longer useful life periods and shorter lead time compared to the MY 2031 standards in proposed Option 1. The test data we currently have from our engine demonstration program is not sufficient to conclude that the Alternative standards would be feasible in the MY2027 timeframe; we would need additional data before we could project that the Alternative is feasible for the MY 2027 timeframe.

We continue to believe it is appropriate for SI and CI engines to have numerically identical standards for the criteria pollutants. As described in Section III, the proposed standards for each pollutant are primarily based on the engine type (CI and SI) for which the particular emission standard is most challenging to achieve. The NO_X standards in proposed Options 1 and 2 are based primarily on emission test data from CI engine demonstration work, while the HC and CO standards in the proposed Options 1 and 2 are based on the SI engine demonstration program. Currently available engine demonstration test data show that the heavy-duty CI engine technologies we are evaluating can achieve a 75 to 90 percent reduction from current NO_X standards. These data indicate that the NO_X standards for MY 2027 in proposed Options 1 and 2 are achievable for a useful life period of 600,000 miles, which encompasses the proposed Option 2 useful life periods for Light HDE and Medium HDEs. Our evaluation of the current data suggests that the proposed Option 2 standards would also be feasible out to the proposed Option 2 Heavy HDE useful life; we are continuing to collect data to confirm our extrapolation of data out to the longer HDE useful life mileage. As discussed in Section IV.A, useful life mileages for proposed Option 2 are higher than the MY 2027 useful life values in proposed Option 1, but lower than the MY 2031 useful life values in proposed Option 1. The useful life mileages included in the proposed Options 1 and 2 are based on the operational life of engines in the field today. Data show that heavy-duty engines are operating in the real world well beyond the useful life periods in our existing regulations, and thus we are proposing longer useful life periods to ensure that emission control systems are durable for an appropriate portion of their use in the real world (see Section IV for details). For the Alternative, data suggest that to meet the combination of numeric levels of the Alternative NO_X emission standards and useful life periods for Light HDEs and Medium HDEs, it may be appropriate for EPA to consider providing manufacturers with additional lead time, beyond the MY 2027 implementation date of the Alternative. For Heavy HDEs, our evaluation of current data suggests that wholly different emission control technologies than we have evaluated to date ( i.e., not based on CDA and a dual SCR) would be needed to meet the Alternative NO_X standards for Heavy HDEs; we request comment on this conclusion and on the availability, or potential development and timeline, of such additional technologies.

Our demonstration test data do show that CI engines can achieve the PM, HC, and CO standards in proposed Options 1 and 2, each of which would result in at least a 50 percent reduction from current emission standards for PM, HC, and CO. The HC and CO standards in the proposed Options 1 and 2, are based on SI engine demonstration data with a catalyst aged beyond the useful life of those scenarios. Available data indicate that the combination of NO_X, HC, and CO emission levels over the longer useful life period reflected in the SI standards of the Alternative would be very challenging to meet in the MY 2027 timeframe. In contrast, we believe the additional lead time provided by the second step of the MY 2031 standards in proposed Option 1, combined with the higher numeric standard for HC and the shorter useful life mileage, results in the MY 2031 standards in proposed Option 1 being both feasible and technology forcing.

We are also proposing to require onboard refueling vapor recovery (ORVR) for incomplete vehicles over 14,000 lb GVWR fueled by gasoline and other volatile fuels. Currently, hydrocarbon vapors from those vehicles are uncontrolled during refueling events, despite technology to control these emissions being widely adopted in vehicles in lower weight classes for almost 20 years. Recent data show this lack of emission control technology can result in refueling emissions that are more than 10 times current light-duty refueling standards (see Section III.D.2 for more discussion). We included ORVR in the analysis of both proposed Options 1 and 2, as well as the Alternative.

Our PM standards are based on certification test data that show the proposed 50 percent reduction in the current PM standard is achievable in CI and SI heavy-duty engines being certified today; the same reduction in PM standard is included in both proposed Options 1 and 2, as well as the Alternative. We believe lowering the PM standard to a level currently achievable through the use of emission control technology used in new engines being sold today is appropriate. EPA is not aware of any technology that is feasible to adopt in the 2027 timeframe that would reduce PM emissions further, and variability in PM measurement starts to increase at PM levels lower than the proposed standard. Nevertheless, we request comment on if there are technologies that EPA could consider that would enable a PM standard lower than 5 mg/hp-hr.

The proposed Options 1 and 2 generally represent the range of options, including the NO_X , HC, and CO standards, useful life periods and lead time that we are currently considering in this rule; we expect we may receive additional information through public comments or data we continue to collect on the feasibility, costs, and other impacts of the proposed Options 1 and 2. In order to consider adopting the Alternative in the final rule, we would need additional information to be able to conclude that the Alternative is feasible in the MY 2027 timeframe. We request comment on all aspects of the proposal, including the revised emission standards and useful life and warranty periods, one and two-step approaches, model years of implementation in proposed Options 1 and 2, or other alternatives roughly within the range of options covered by the proposed Options 1 and 2, as well as other provisions described in this proposal. We also request comment, including relevant data and other information, related to the feasibility of the implementation model year, numeric levels of the emission standards, and useful life and warranty periods included in the Alternative, or other alternatives outside the range of options covered by the proposed Options 1 and 2.

As described in Section III, we are proposing new laboratory test duty cycles and standards in response to data that show a current lack of emission control under low-load conditions in CI heavy-duty engines, and under high-load in SI heavy-duty engines. As noted in Section VI, we project that without the proposed provisions, low- and high-load engine operations would account for 28 and 36 percent, respectively, of the heavy-duty NO_X emission inventory in 2045.

Proposed Option 1 includes requirements for lowering the numeric level of the standard and lengthening useful life in two steps. Consistent with our approach for useful life, proposed Option 1 would lengthen emission warranty mileages in two steps, such that the proposed MY 2031 warranty would cover an appropriate portion of the proposed MY 2031 regulatory useful life (see Section IV.B for more discussion). The proposed Option 2 would lengthen emission warranty mileages in a single step, consistent with the proposed single step increase in useful life in proposed Option 2. While warranty periods do not directly impact the stringency of the proposed standards, we expect the proposed lengthened warranty periods would improve air quality and we included them in our inventory and cost analyses of the proposed Option 1 and Option 2 standards.

We are also proposing additional compliance provisions that would begin in MY 2027, such as targeted provisions to help ensure that owners can efficiently maintain emissions performance over the operational life of the engine. We are proposing provisions to enhance communication with operators, including updated diagnostic requirements, a revised inducement policy for SCR-based aftertreatment systems, and improved access to service information (see Section IV.B for more discussion). We believe these proposed provisions could decrease the likelihood that owners tamper with ( i.e., remove or otherwise disable) emission control systems.

The emission reductions from the proposed program would increase over time as more new, cleaner vehicles enter the fleet. For example, by 2040 the proposed Option 1 would reduce heavy-duty NO_X emissions by more than 55 percent, compared to projected 2040 emissions without the proposed rule. The proposed Option 2 would reduce heavy-duty NO_X emissions by 44 percent in 2040 (see Section VI for details on projected emission reductions from proposed Option 1 or 2). These emission reductions would lower ambient concentrations of pollutants such as ozone and PM_2.5 . Our analysis shows that the proposed Option 1 would provide more emission reductions than proposed Option 2, and less reductions than the Alternative. Our air quality modeling analysis of Option 1's projected emission reductions shows widespread reductions in ambient concentrations of air pollutants in 2045, which is a year by which most of the regulated fleet would have turned over. Our analysis shows that these emission reductions would result in significant improvements in ozone concentrations; ambient PM_2.5, NO₂ and CO concentrations would also improve in 2045 (see Section VII for details). Based on our air quality analysis of PM_2.5 and ozone, we estimate that in 2045, the proposed Option 1 would result in total annual monetized health benefits of $12 and $33 billion at a 3 percent discount rate and $10 and $30 billion at a 7 percent discount rate (2017 dollars). We estimate that in 2045, the proposed Option 2 would result in total annual monetized health benefits of $9 and $26 billion at a 3 percent discount rate and $8 and $23 billion at a 7 percent discount rate (2017 dollars) (see Section VIII for details).

In addition to projected health benefits, we considered several other factors in developing the proposed standards, including cost, energy, and safety. Our cost analysis, presented in Section V, accounts for costs to manufacturers and to truck owners. Costs to manufacturers include direct manufacturing costs ( i.e., new hardware/technology) and indirect costs ( e.g., emission warranty, R&D), while costs to truck owners include operating costs ( e.g., fuel, diesel exhaust fluid, emission control system repairs). Our analysis shows that direct manufacturing costs are the same for proposed Options 1 and 2; however, indirect costs result in total costs to manufacturers ( i.e., total technology costs) under the proposed Option 1 being slightly higher than under the proposed Option 2. The operating costs associated with the proposed Option 1 are estimated to be lower than those of proposed Option 2. The lower operating costs in proposed Option 1 (largely from lower repair costs) offset the higher technology costs (due to higher warranty and R&D driven indirect costs) in proposed Option 1, which results in a lower total cost of proposed Option 1 relative to proposed Option 2 when costs are summed for 2027 through 2045. For the Alternative, we have not determined the incremental direct manufacturing costs of the technology needed to meet the standards, and we would need additional data before we could project that the Alternative is feasible for the MY 2027 timeframe.

Section IX compares the benefits and costs of the proposed Options 1 and 2. Our analysis shows that while proposed Option 2 provides higher emission reductions in the early years of the program, it has lower net benefits than proposed Option 1 when considering the time period of 2027 through 2045; this is a result of both higher costs and lower emission reductions relative to proposed Option 1 in the later years of the program. As noted throughout this section and discussed in Sections III and IV, we do not currently have information to project that the Alternative standards as currently formulated are feasible in the MY 2027 timeframe with the emission control technologies we evaluated to date, and thus we are not presenting an analysis of the costs or benefits of the Alternative.

Our current evaluation of available data shows that the standards and useful life periods in both steps of proposed Option 1 are feasible and that each step would result in the greatest degree of emission reduction achievable for the model years to which they are proposed to apply, pursuant to CAA section 202(a)(3), giving appropriate consideration to cost, lead time, and other factors. Our analysis further shows that the standards and useful life periods in proposed Option 2 are feasible in the 2027 model year, but would result in lower levels of emission reductions compared to proposed Option 1. Given the analysis we present in this proposal, we currently believe that proposed Option 1 may be a more appropriate level of stringency as it would result in a greater level of achievable emission reduction for the model years proposed, which is consistent with EPA's statutory authority under Clean Air Act section 202(a)(3). However, as further discussed in Section III and draft RIA Chapter 3, we expect that additional data from EPA's ongoing work to demonstrate the performance of emission control technologies, as well as information received in public comments, will allow us to refine our assessments and consideration of the feasibility of the combination of the standards and useful life periods, particularly for the largest CI engines (HHDEs), in proposed Options 1 and 2, after consideration of lead time, costs, and other factors. Therefore, we are co-proposing Options 1 and 2 standards and useful life periods, and the range of options in between them, as the options that may potentially be appropriate to finalize pursuant to CAA section 202(a)(3) once EPA has considered that additional data and other information.

Our analysis further shows that the proposed Option 1 and 2 standards would have no negative impacts on energy; as discussed in Section III, our evaluation of test engine data shows no change in energy consumption ( i.e., fuel) relative to a baseline engine. Similarly, we anticipate no negative impacts on safety due to the proposed program.

2. Basis of the Targeted Revisions to the HD GHG Phase 2 Program

In addition to the proposed criteria pollutant program provisions, we are proposing targeted updates to certain CO₂ standards for MY 2027 trucks, and we are requesting comment on updates to the advanced technology incentive program for electric vehicles. The transportation sector is the largest U.S. source of GHG emissions, representing 29 percent of total GHG emissions. Within the transportation sector, heavy-duty vehicles are the second largest contributor, at 23 percent. GHG emissions have significant impacts on public health and welfare as evidenced by the well-documented scientific record and as set forth in EPA's Endangerment and Cause or Contribute Findings under CAA section 202(a). Therefore, continued emission reductions in the heavy-duty vehicle sector are appropriate.

We are at the early stages of a significant transition in the history of the heavy-duty on-highway sector—a shift to zero-emission vehicle technologies. This change is underway and presents an opportunity for significant reductions in heavy-duty GHG emissions. Major trucking fleets, manufacturers and U.S. states have announced plans to shift the heavy-duty fleet toward zero-emissions technology beyond levels we accounted for in setting the existing HD GHG Phase 2 standards, as detailed in Section XI. Specifically, we set the existing Phase 2 standards at levels that would require all conventional vehicles to install varying combinations of emission-control technologies (the degree and types of technology can differ, with some vehicles that have less being offset by others with more, which would lead to CO₂ emissions reductions). As discussed in Section XI, the rise in electrification beyond what we had anticipated when finalizing the HD GHG Phase 2 program ( e.g., the California Advanced Clean Trucks rulemaking) would enable manufacturers to produce some conventional vehicles without installing any of the GHG emission-reducing technologies that we projected in the HD GHG Phase 2 rulemaking, absent the changes we are proposing in this document.

To address this issue, EPA is proposing under its authority in CAA section 202(a) to revise GHG emissions standards for a subset of MY 2027 heavy-duty vehicles. Specifically, we propose to adjust HD Phase 2 vehicle GHG emission standards by sales-weighting the projected EV production levels of school buses, transit buses, delivery trucks, and short-haul tractors and by lowering the applicable GHG emission standards in MY 2027 accordingly. Our proposed approach adjusts 17 of the 33 MY 2027 Phase 2 vocational vehicle and tractor standards and does not change any MY 2021 or MY 2024 standards or any of the Class 2b/3 pickup truck and van standards. In addition, we are requesting comment on potential changes to the advanced technology incentive program for electric vehicles beginning in MY 2024.

Under CAA section 202(a), emission standards take effect “after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.” Thus, in establishing or revising CAA section 202(a) standards, EPA must consider issues of technological feasibility, compliance cost, and lead time. The proposed revised standards are based on the same technology packages used to derive the current HD GHG Phase 2 standards, which we applied to the subset of the vehicles that would otherwise not require GHG-reducing technologies due to the higher projection of HD electric vehicles in MY 2027 and beyond and the incentive program. The HD GHG Phase 2 standards were based on adoption rates for technologies in technology packages that EPA regards as appropriate under CAA section 202(a) for the reasons given in the HD GHG Phase 2 rulemaking in Section III.D.1 for tractors and Section V.C.1 for vocational vehicles. We continue to believe these technologies can be adopted at the estimated technology adoption rates for these proposed revised standards within the lead time that would be provided. The fleet-wide average cost per tractor projected to meet the proposed revised MY 2027 standards is approximately $10,200 to $10,500. The fleet-wide average cost per vocational vehicle to meet the proposed revised MY 2027 standards ranges between $1,500 and $5,700. These increased costs would be recovered in the form of fuel savings during the first two years of ownership for tractors and first four years for vocational vehicles, which we still consider to be reasonable. In addition, manufacturers would retain leeway to develop alternative compliance paths, increasing the likelihood of the proposed revised standards' successful implementation. The targeted adjustments to the select standards we are proposing would result in modest CO₂ emissions reductions and climate-related benefits associated with these emission reductions. As described in more detail in Section XI, we believe this proposal considered feasibility, cost, lead time, emissions impact, and other relevant factors, and therefore these standards are appropriate under CAA section 202(a).

In addition to these proposed standard adjustments, we are requesting comment on options to update the advanced technology incentive program for electric and plug-in hybrid vehicles beginning in MY 2024. These changes may be appropriate to reflect that such levels of incentives for electrification may no longer be appropriate for certain segments of the HD EV market. We are interested in trying to balance providing incentivizes for the continued development of zero and near-zero emission vehicles without inadvertently undermining the GHG emission reductions expected from the existing HD GHG Phase 2 program with inappropriate incentives.

II. Need for Additional Emissions Control

This proposal would reduce emissions from heavy-duty engines that contribute to ambient levels of ozone, PM, NO_X and CO, which are all pollutants for which EPA has established health-based NAAQS. These pollutants are linked to premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. Many groups are at greater risk than healthy people from these pollutants, including people with heart or lung disease, outdoor workers, older adults and children. These pollutants also reduce visibility and negatively impact ecosystems. This proposal would also reduce emissions of air toxics from heavy-duty engines. A more detailed discussion of the health and environmental effects associated with the pollutants affected by this proposed rule is included in Sections II.B and II.C and Chapter 4 of the draft RIA.

As further described in Sections II.B.7 and II.B.8, populations who live, work, or go to school near high-traffic roadways experience higher rates of numerous adverse health effects, compared to populations far away from major roads. In addition, there is substantial evidence that people who live or attend school near major roadways are more likely to be people of color, Hispanic ethnicity, and/or low socioeconomic status.

Across the U.S., NO_X emissions from heavy-duty engines are important contributors to concentrations of ozone and PM_2.5 and their resulting threat to public health. The emissions modeling done for the proposed rule (see Chapter 5 of the draft RIA) indicates that heavy-duty engines will continue to be one of the largest contributors to mobile source NO_X emissions nationwide in the future, representing 32 percent of the mobile source NO_X in calendar year 2045. Furthermore, it is estimated that heavy-duty engines will represent 89 percent of the onroad NO_X inventory in calendar year 2045. The emission reductions that would occur from the proposed rule are projected to reduce air pollution that is (and is projected to continue to be) at levels that endanger public health and welfare.

Many state and local agencies across the country have asked the EPA to further reduce NO_X emissions, specifically from heavy-duty engines, because such reductions will be a critical part of many areas' strategies to attain and maintain the ozone and PM NAAQS. These state and local agencies anticipate challenges in attaining the NAAQS, maintaining the NAAQS in the future, and/or preventing nonattainment. Some nonattainment areas have already been “bumped up” to higher classifications because of challenges in attaining the NAAQS; others say they are struggling to avoid nonattainment. Many state and local agencies commented on the ANPR that heavy-duty vehicles are one of their largest sources of NO_X emissions. They commented that without action to reduce emissions from heavy-duty vehicles, they would have to adopt other potentially more burdensome and costly measures to reduce emissions from other sources under their state or local authority, such as local businesses. More information on the projected emission reductions and air quality impacts that would result from this proposed rule is provided in Sections VI and VII.

In their comments on the ANPR, environmental groups as well as state, local, and Tribal agencies supported additional NO_X reductions from heavy-duty vehicles to address concerns about environmental justice and ensuring that all communities benefit from improvements in air quality. Commenters also supported additional NO_X reductions from heavy-duty vehicles in order to address concerns about regional haze, and damage to terrestrial and aquatic ecosystems. They mentioned the impacts of NO_X emissions on numerous locations, such as the Chesapeake Bay, Narragansett Bay, Long Island Sound, Joshua Tree National Park and the surrounding Mojave Desert, the Adirondacks, and other areas. Tribes and agencies commented that NO_X deposition into lakes is harmful to fish and other aquatic life forms on which they depend for subsistence livelihoods. They also commented that regional haze and increased rates of weathering caused by pollution are of particular concern and can damage culturally significant archeological sites.

A. Background on Pollutants Impacted by This Proposal

1. Ozone

Ground-level ozone pollution forms in areas with high concentrations of ambient NO_X and VOCs when solar radiation is strong. Major U.S. sources of NO_X are highway and nonroad motor vehicles, engines, power plants and other industrial sources, with natural sources, such as soil, vegetation, and lightning, serving as smaller sources. Vegetation is the dominant source of VOCs in the U.S. Volatile consumer and commercial products, such as propellants and solvents, highway and nonroad vehicles, engines, fires, and industrial sources also contribute to the atmospheric burden of VOCs at ground-level.

The processes underlying ozone formation, transport, and accumulation are complex. Ground-level ozone is produced and destroyed by an interwoven network of free radical reactions involving the hydroxyl radical (OH), NO, NO₂, and complex reaction intermediates derived from VOCs. Many of these reactions are sensitive to temperature and available sunlight. High ozone events most often occur when ambient temperatures and sunlight intensities remain high for several days under stagnant conditions. Ozone and its precursors can also be transported hundreds of miles downwind which can lead to elevated ozone levels in areas with otherwise low VOC or NO_X emissions. As an air mass moves and is exposed to changing ambient concentrations of NO_X and VOCs, the ozone photochemical regime (relative sensitivity of ozone formation to NO_X and VOC emissions) can change.

When ambient VOC concentrations are high, comparatively small amounts of NO_X catalyze rapid ozone formation. Without available NO_X, ground-level ozone production is severely limited, and VOC reductions would have little impact on ozone concentrations. Photochemistry under these conditions is said to be “NO_X -limited.” When NO_X levels are sufficiently high, faster NO₂ oxidation consumes more radicals, dampening ozone production. Under these “VOC-limited” conditions (also referred to as ” NO_X -saturated” conditions), VOC reductions are effective in reducing ozone, and NO_X can react directly with ozone resulting in suppressed ozone concentrations near NO_X emission sources. Under these NO_X -saturated conditions, NO_X reductions can actually increase local ozone under certain circumstances, but overall ozone production (considering downwind formation) decreases and even in VOC-limited areas, NO_X reductions are not expected to increase ozone levels if the NO_X reductions are sufficiently large—large enough to become NO_X -limited.

The primary NAAQS for ozone, established in 2015 and retained in 2020, is an 8-hour standard with a level of 0.07 ppm. EPA recently announced that it will reconsider the previous administration's decision to retain the ozone NAAQS. The EPA is also implementing the previous 8-hour ozone primary standard, set in 2008, at a level of 0.075 ppm. As of May 31, 2021, there were 34 ozone nonattainment areas for the 2008 ozone NAAQS, composed of 151 full or partial counties, with a population of more than 99 million, and 50 ozone nonattainment areas for the 2015 ozone NAAQS, composed of 205 full or partial counties, with a population of more than 122 million. In total, there are currently, as of May 31, 2021, 57 ozone nonattainment areas with a population of more than 122 million people.

States with ozone nonattainment areas are required to take action to bring those areas into attainment. The attainment date assigned to an ozone nonattainment area is based on the area's classification. The attainment dates for areas designated nonattainment for the 2008 8-hour ozone NAAQS are in the 2015 to 2032 timeframe, depending on the severity of the problem in each area. Attainment dates for areas designated nonattainment for the 2015 ozone NAAQS will be in the 2021 to 2038 timeframe, again depending on the severity of the problem in each area. The proposed rule would begin to take effect in MY 2027 and would assist areas with attaining the NAAQS and may relieve areas with already stringent local regulations from some of the burden associated with adopting additional local controls. The proposed rule could also provide assistance to counties with ambient concentrations near the level of the NAAQS who are working to ensure long-term attainment or maintenance of the NAAQS.

2. Particulate Matter

Particulate matter (PM) is a complex mixture of solid particles and liquid droplets distributed among numerous atmospheric gases which interact with solid and liquid phases. Particles in the atmosphere range in size from less than 0.01 to more than 10 micrometers (μm) in diameter. Atmospheric particles can be grouped into several classes according to their aerodynamic diameter and physical sizes. Generally, the three broad classes of particles include ultrafine particles (UFPs, generally considered as particles with a diameter less than or equal to 0.1 μm [typically based on physical size, thermal diffusivity or electrical mobility]), “fine” particles (PM_2.5; particles with a nominal mean aerodynamic diameter less than or equal to 2.5 μm), and “thoracic” particles (PM₁₀; particles with a nominal mean aerodynamic diameter less than or equal to 10 μm). Particles that fall within the size range between PM_2.5 and PM₁₀, are referred to as “thoracic coarse particles” (PM_10-2.5, particles with a nominal mean aerodynamic diameter greater than 2.5 μm and less than or equal to 10 μm). EPA currently has NAAQS for PM_2.5 and PM₁₀ .

Most particles are found in the lower troposphere, where they can have residence times ranging from a few hours to weeks. Particles are removed from the atmosphere by wet deposition, such as when they are carried by rain or snow, or by dry deposition, when particles settle out of suspension due to gravity. Atmospheric lifetimes are generally longest for PM_2.5 , which often remains in the atmosphere for days to weeks before being removed by wet or dry deposition. In contrast, atmospheric lifetimes for UFP and PM_10-2.5 are shorter. Within hours, UFP can undergo coagulation and condensation that lead to formation of larger particles in the accumulation mode, or can be removed from the atmosphere by evaporation, deposition, or reactions with other atmospheric components. PM_10-2.5 are also generally removed from the atmosphere within hours, through wet or dry deposition.

Particulate matter consists of both primary and secondary particles. Primary particles are emitted directly from sources, such as combustion-related activities ( e.g., industrial activities, motor vehicle operation, biomass burning), while secondary particles are formed through atmospheric chemical reactions of gaseous precursors ( e.g., sulfur oxides (SO_X), nitrogen oxides (NO_X) and volatile organic compounds (VOCs)). From 2000 to 2017, national annual average ambient PM_2.5 concentrations have declined by over 40 percent, largely reflecting reductions in emissions of precursor gases.

There are two primary NAAQS for PM_2.5: An annual standard (12.0 micrograms per cubic meter (μg/m3)) and a 24-hour standard (35 μg/m3), and there are two secondary NAAQS for PM_2.5: An annual standard (15.0 μg/m3) and a 24-hour standard (35 μg/m3). The initial PM_2.5 standards were set in 1997 and revisions to the standards were finalized in 2006 and in December 2012 and then retained in 2020. On June 10, 2021, EPA announced that it will reconsider the previous administration's decision to retain the PM NAAQS.

There are many areas of the country that are currently in nonattainment for the annual and 24-hour primary PM_2.5 NAAQS. As of May 31, 2021, more than 19 million people lived in the 4 areas that are designated as nonattainment for the 1997 PM_2.5 NAAQS. Also, as of May 31, 2021, more than 31 million people lived in the 14 areas that are designated as nonattainment for the 2006 PM_2.5 NAAQS and more than 20 million people lived in the 6 areas designated as nonattainment for the 2012 PM_2.5 NAAQS. In total, there are currently 17 PM_2.5 nonattainment areas with a population of more than 32 million people. The proposed rule would take effect in MY 2027 and would assist areas with attaining the NAAQS and may relieve areas with already stringent local regulations from some of the burden associated with adopting additional local controls. The proposed rule would also assist counties with ambient concentrations near the level of the NAAQS who are working to ensure long-term attainment or maintenance of the PM_2.5 NAAQS.

3. Nitrogen Oxides

Oxides of nitrogen (NO_X) refers to nitric oxide (NO) and nitrogen dioxide (NO₂). Most NO₂ is formed in the air through the oxidation of nitric oxide (NO) emitted when fuel is burned at a high temperature. NO_X is a criteria pollutant, regulated for its adverse effects on public health and the environment, and highway vehicles are an important contributor to NO_X emissions. NO_X, along with VOCs, are the two major precursors of ozone and NO_X is also a major contributor to secondary PM_2.5 formation. There are two primary NAAQS for NO₂ : An annual standard (53 ppb) and a 1-hour standard (100 ppb). In 2010, EPA established requirements for monitoring NO₂ near roadways expected to have the highest concentrations within large cities. Monitoring within this near-roadway network began in 2014, with additional sites deployed in the following years. At present, there are no nonattainment areas for NO₂ .

4. Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes. Nationally, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources. There are two primary NAAQS for CO: An 8-hour standard (9 ppm) and a 1-hour standard (35 ppm). There are currently no CO nonattainment areas; as of September 27, 2010, all CO nonattainment areas have been redesignated to attainment. The past designations were based on the existing community-wide monitoring network. EPA made an addition to the ambient air monitoring requirements for CO during the 2011 NAAQS review. Those new requirements called for CO monitors to be operated near roads in Core Based Statistical Areas (CBSAs) of 1 million or more persons, in addition to the existing community-based network (76 FR 54294, August 31, 2011).

5. Diesel Exhaust

Diesel exhaust is a complex mixture composed of particulate matter, carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide, nitrogen compounds, sulfur compounds and numerous low-molecular-weight hydrocarbons. A number of these gaseous hydrocarbon components are individually known to be toxic, including aldehydes, benzene and 1,3-butadiene. The diesel particulate matter present in diesel exhaust consists mostly of fine particles (<2.5 μm), of which a significant fraction is ultrafine particles (<0.1 μm). These particles have a large surface area which makes them an excellent medium for adsorbing organics and their small size makes them highly respirable. Many of the organic compounds present in the gases and on the particles, such as polycyclic organic matter, are individually known to have mutagenic and carcinogenic properties.

Diesel exhaust varies significantly in chemical composition and particle sizes between different engine types (heavy-duty, light-duty), engine operating conditions (idle, acceleration, deceleration), and fuel formulations (high/low sulfur fuel). Also, there are emissions differences between on-road and nonroad engines because the nonroad engines are generally of older technology. After being emitted in the engine exhaust, diesel exhaust undergoes dilution as well as chemical and physical changes in the atmosphere. The lifetime of the components present in diesel exhaust ranges from seconds to days.

Because diesel particulate matter (DPM) is part of overall ambient PM, varies considerably in composition, and lacks distinct chemical markers that enable it to be easily distinguished from overall primary PM, we do not have direct measurements of DPM in the ambient air. DPM concentrations are estimated using ambient air quality modeling based on DPM emission inventories. DPM emission inventories are computed as the exhaust PM emissions from mobile sources combusting diesel or residual oil fuel. DPM concentrations were estimated as part of the 2014 National Air Toxics Assessment (NATA). Areas with high concentrations are clustered in the Northeast, Great Lake States, California, and the Gulf Coast States, with the highest impacts occurring in major urban cores, and are also distributed throughout the rest of the U.S. Approximately half of average ambient DPM in the U.S. can be attributed to heavy-duty diesel engines, with the remainder attributable to nonroad engines.

6. Air Toxics

The most recent available data indicate that the majority of Americans continue to be exposed to ambient concentrations of air toxics at levels which have the potential to cause adverse health effects. The levels of air toxics to which people are exposed vary depending on where people live and work and the kinds of activities in which they engage, as discussed in detail in EPA's 2007 Mobile Source Air Toxics Rule. According to the National Air Toxic Assessment (NATA) for 2014, mobile sources were responsible for over 40 percent of outdoor anthropogenic toxic emissions and were the largest contributor to national average cancer and noncancer risk from directly emitted pollutants. Mobile sources are also significant contributors to precursor emissions which react to form air toxics. Formaldehyde is the largest contributor to cancer risk of all 71 pollutants quantitatively assessed in the 2014 NATA. Mobile sources were responsible for more than 25 percent of primary anthropogenic emissions of this pollutant in 2014 and are significant contributors to formaldehyde precursor emissions. Benzene is also a large contributor to cancer risk, and mobile sources account for almost 70 percent of ambient exposure.

B. Health Effects Associated With Exposure to Pollutants Impacted by This Proposal

Heavy duty engines emit pollutants that contribute to ambient concentrations of ozone, PM, NO₂, CO, and air toxics. A discussion of the health effects associated with exposure to these pollutants, and a discussion on environmental justice, is included in this section of the preamble. Additionally, children are recognized to have increased vulnerability and susceptibility related to air pollution and other environmental exposures; this is discussed further in Section XIII of the Preamble. Information on emission reductions and air quality impacts from this proposed rule are included in Section VI and VII of this preamble.

1. Ozone

This section provides a summary of the health effects associated with exposure to ambient concentrations of ozone. The information in this section is based on the information and conclusions in the April 2020 Integrated Science Assessment for Ozone (Ozone ISA). The Ozone ISA concludes that human exposures to ambient concentrations of ozone are associated with a number of adverse health effects and characterizes the weight of evidence for these health effects. The discussion below highlights the Ozone ISA's conclusions pertaining to health effects associated with both short-term and long-term periods of exposure to ozone.

For short-term exposure to ozone, the Ozone ISA concludes that respiratory effects, including lung function decrements, pulmonary inflammation, exacerbation of asthma, respiratory-related hospital admissions, and mortality, are causally associated with ozone exposure. It also concludes that metabolic effects, including metabolic syndrome ( i.e., changes in insulin or glucose levels, cholesterol levels, obesity and blood pressure) and complications due to diabetes are likely to be causally associated with short-term exposure to ozone and that evidence is suggestive of a causal relationship between cardiovascular effects, central nervous system effects and total mortality and short-term exposure to ozone.

For long-term exposure to ozone, the Ozone ISA concludes that respiratory effects, including new onset asthma, pulmonary inflammation and injury, are likely to be causally related with ozone exposure. The Ozone ISA characterizes the evidence as suggestive of a causal relationship for associations between long-term ozone exposure and cardiovascular effects, metabolic effects, reproductive and developmental effects, central nervous system effects and total mortality. The evidence is inadequate to infer a causal relationship between chronic ozone exposure and increased risk of cancer.

Finally, interindividual variation in human responses to ozone exposure can result in some groups being at increased risk for detrimental effects in response to exposure. In addition, some groups are at increased risk of exposure due to their activities, such as outdoor workers and children. The Ozone ISA identified several groups that are at increased risk for ozone-related health effects. These groups are people with asthma, children and older adults, individuals with reduced intake of certain nutrients ( i.e., Vitamins C and E), outdoor workers, and individuals having certain genetic variants related to oxidative metabolism or inflammation. Ozone exposure during childhood can have lasting effects through adulthood. Such effects include altered function of the respiratory and immune systems. Children absorb higher doses (normalized to lung surface area) of ambient ozone, compared to adults, due to their increased time spent outdoors, higher ventilation rates relative to body size, and a tendency to breathe a greater fraction of air through the mouth. Children also have a higher asthma prevalence compared to adults. Recent epidemiologic studies provide generally consistent evidence that long-term ozone exposure is associated with the development of asthma in children. Studies comparing age groups reported higher magnitude associations for short-term ozone exposure and respiratory hospital admissions and emergency room visits among children than for adults. Panel studies also provide support for experimental studies with consistent associations between short-term ozone exposure and lung function and pulmonary inflammation in healthy children. Additional children's vulnerability and susceptibility factors are listed in Section XIII of the Preamble.

2. Particulate Matter

Scientific evidence spanning animal toxicological, controlled human exposure, and epidemiologic studies shows that exposure to ambient PM is associated with a broad range of health effects. These health effects are discussed in detail in the Integrated Science Assessment for Particulate Matter (PM ISA), which was finalized in December 2019. The PM ISA characterizes the causal nature of relationships between PM exposure and broad health categories ( e.g., cardiovascular effects, respiratory effects, etc.) using a weight-of-evidence approach. Within this characterization, the PM ISA summarizes the health effects evidence for short- and long-term exposures to PM_2.5, PM_10-2.5, and ultrafine particles, and concludes that human exposures to ambient PM_2.5 are associated with a number of adverse health effects. The discussion below highlights the PM ISA's conclusions pertaining to the health effects evidence for both short- and long-term PM exposures. Further discussion of PM-related health effects can also be found in the 2020 Policy Assessment for the review of the PM NAAQS.

EPA has concluded that recent evidence in combination with evidence evaluated in the 2009 PM ISA supports a “causal relationship” between both long- and short-term exposures to PM_2.5 and mortality and cardiovascular effects and a “likely to be causal relationship” between long- and short-term PM_2.5 exposures and respiratory effects. Additionally, recent experimental and epidemiologic studies provide evidence supporting a “likely to be causal relationship” between long-term PM_2.5 exposure and nervous system effects, and long-term PM_2.5 exposure and cancer. In addition, EPA noted that there was more limited and uncertain evidence for long-term PM_2.5 exposure and reproductive and developmental effects ( i.e., male/female reproduction and fertility; pregnancy and birth outcomes), long- and short-term exposures and metabolic effects, and short-term exposure and nervous system effects resulting in the ISA concluding “suggestive of, but not sufficient to infer, a causal relationship.”

As discussed extensively in the 2019 PM ISA, recent studies continue to support and extend the evidence base linking short- and long-term PM_2.5 exposures and mortality. For short-term PM_2.5 exposure, recent multi-city studies, in combination with single- and multi-city studies evaluated in the 2009 PM ISA, provide evidence of consistent, positive associations across studies conducted in different geographic locations, populations with different demographic characteristics, and studies using different exposure assignment techniques. Additionally, the consistent and coherent evidence across scientific disciplines for cardiovascular morbidity, particularly ischemic events and heart failure, and to a lesser degree for respiratory morbidity, with the strongest evidence for exacerbations of chronic obstructive pulmonary disease (COPD) and asthma, provide biological plausibility for cause-specific mortality and ultimately total mortality.

In addition to reanalyses and extensions of the American Cancer Society (ACS) and Harvard Six Cities (HSC) cohorts, multiple new cohort studies conducted in the U.S. and Canada consisting of people employed in a specific job ( e.g., teacher, nurse), and that apply different exposure assignment techniques provide evidence of positive associations between long-term PM_2.5 exposure and mortality. Biological plausibility for mortality due to long-term PM_2.5 exposure is provided by the coherence of effects across scientific disciplines for cardiovascular morbidity, particularly for coronary heart disease (CHD), stroke and atherosclerosis, and for respiratory morbidity, particularly for the development of COPD. Additionally, recent studies provide evidence indicating that as long-term PM_2.5 concentrations decrease there is an increase in life expectancy.

A large body of recent studies examining both short- and long-term PM_2.5 exposure and cardiovascular effects supports and extends the evidence base evaluated in the 2009 PM ISA. Some of the strongest evidence from both experimental and epidemiologic studies examining short-term PM_2.5 exposures are for ischemic heart disease (IHD) and heart failure. The evidence for cardiovascular effects is coherent across studies of short-term PM_2.5 exposure that have observed associations with a continuum of effects ranging from subtle changes in indicators of cardiovascular health to serious clinical events, such as increased emergency department visits and hospital admissions due to cardiovascular disease and cardiovascular mortality. For long-term PM_2.5 exposure, there is strong and consistent epidemiologic evidence of a relationship with cardiovascular mortality. This evidence is supported by epidemiologic and animal toxicological studies demonstrating a range of cardiovascular effects including coronary heart disease, stroke, impaired heart function, and subclinical markers ( e.g., coronary artery calcification, atherosclerotic plaque progression), which collectively provide coherence and biological plausibility.

Recent studies continue to provide evidence of a relationship between both short- and long-term PM_2.5 exposure and respiratory effects. Epidemiologic and animal toxicological studies examining short-term PM_2.5 exposure provide consistent evidence of asthma and COPD exacerbations, in children and adults, respectively. This evidence is supported by epidemiologic studies examining asthma and COPD emergency department visits and hospital admissions, as well as respiratory mortality. However, there is inconsistent evidence of respiratory effects, specifically lung function declines and pulmonary inflammation, in controlled human exposure studies. Epidemiologic studies conducted in the U.S. and abroad provide evidence of a relationship between long-term PM_2.5 exposure and respiratory effects, including consistent changes in lung function and lung function growth rate, increased asthma incidence, asthma prevalence, and wheeze in children; acceleration of lung function decline in adults; and respiratory mortality. The epidemiologic evidence is supported by animal toxicological studies, which provide coherence and biological plausibility for a range of effects including impaired lung development, decrements in lung function growth, and asthma development.

Since the 2009 PM ISA, a growing body of scientific evidence examined the relationship between long-term PM_2.5 exposure and nervous system effects, resulting for the first time in a causality determination for this health effects category. The strongest evidence for effects on the nervous system come from epidemiologic studies that consistently report cognitive decrements and reductions in brain volume in adults. The effects observed in epidemiologic studies are supported by animal toxicological studies demonstrating effects on the brain of adult animals including inflammation, morphologic changes, and neurodegeneration of specific regions of the brain. There is more limited evidence for neurodevelopmental effects in children with some studies reporting positive associations with autism spectrum disorder (ASD) and others providing limited evidence of an association with cognitive function. While there is some evidence from animal toxicological studies indicating effects on the brain ( i.e., inflammatory and morphological changes) to support a biologically plausible pathway, epidemiologic studies of neurodevelopmental effects are limited due to their lack of control for potential confounding by copollutants, the small number of studies conducted, and uncertainty regarding critical exposure windows.

Building off the decades of research demonstrating mutagenicity, DNA damage, and endpoints related to genotoxicity due to whole PM exposures, recent experimental and epidemiologic studies focusing specifically on PM_2.5 provide evidence of a relationship between long-term PM_2.5 exposure and cancer. Epidemiologic studies examining long-term PM_2.5 exposure and lung cancer incidence and mortality provide evidence of generally positive associations in cohort studies spanning different populations, locations, and exposure assignment techniques. Additionally, there is evidence of positive associations in analyses limited to never smokers. The epidemiologic evidence is supported by both experimental and epidemiologic evidence of genotoxicity, epigenetic effects, carcinogenic potential, and that PM_2.5 exhibits several characteristics of carcinogens, which collectively provides biological plausibility for cancer development.

For the additional health effects categories evaluated for PM_2.5 in the 2019 PM ISA, experimental and epidemiologic studies provide limited and/or inconsistent evidence of a relationship with PM_2.5 exposure. As a result, the 2019 PM ISA concluded that the evidence is “suggestive of, but not sufficient to infer a causal relationship” for short-term PM_2.5 exposure and metabolic effects and nervous system effects, and long-term PM_2.5 exposures and metabolic effects as well as reproductive and developmental effects.

In addition to evaluating the health effects attributed to short- and long-term exposure to PM_2.5, the 2019 PM ISA also conducted an extensive evaluation as to whether specific components or sources of PM_2.5 are more strongly related with health effects than PM_2.5 mass. An evaluation of those studies resulted in the 2019 PM ISA concluding that “many PM_2.5 components and sources are associated with many health effects, and the evidence does not indicate that any one source or component is consistently more strongly related to health effects than PM_2.5 mass.”

For both PM_10-2.5 and UFPs, for all health effects categories evaluated, the 2019 PM ISA concluded that the evidence was “suggestive of, but not sufficient to infer, a causal relationship” or “inadequate to determine the presence or absence of a causal relationship.” For PM_10-2.5, although a Federal Reference Method (FRM) was instituted in 2011 to measure PM_10-2.5 concentrations nationally, the causality determinations reflect that the same uncertainty identified in the 2009 PM ISA with respect to the method used to estimate PM_10-2.5 concentrations in epidemiologic studies persists. Specifically, across epidemiologic studies, different approaches are used to estimate PM_10-2.5 concentrations ( e.g., direct measurement of PM_10-2.5, difference between PM₁₀ and PM_2.5 concentrations), and it remains unclear how well correlated PM_10-2.5 concentrations are both spatially and temporally across the different methods used.

For UFPs, the uncertainty in the evidence for the health effect categories evaluated across experimental and epidemiologic studies reflects the inconsistency in the exposure metric used ( i.e., particle number concentration, surface area concentration, mass concentration) as well as the size fractions examined. In epidemiologic studies the size fraction can vary depending on the monitor used and exposure metric, with some studies examining number count over the entire particle size range, while experimental studies that use a particle concentrator often examine particles up to 0.3 μm. Additionally, due to the lack of a monitoring network, there is limited information on the spatial and temporal variability of UFPs within the U.S., as well as population exposures to UFPs, which adds uncertainty to epidemiologic study results.

The 2019 p.m. ISA cites extensive evidence indicating that “both the general population as well as specific populations and life stages are at risk for PM_2.5 -related health effects.” For example, in support of its “causal” and “likely to be causal” determinations, the ISA cites substantial evidence for (1) PM-related mortality and cardiovascular effects in older adults; (2) PM-related cardiovascular effects in people with pre-existing cardiovascular disease; (3) PM-related respiratory effects in people with pre-existing respiratory disease, particularly asthma exacerbations in children; and (4) PM-related impairments in lung function growth and asthma development in children. The ISA additionally notes that stratified analyses ( i.e., analyses that directly compare PM-related health effects across groups) provide strong evidence for racial and ethnic differences in PM_2.5 exposures and in the risk of PM_2.5 -related health effects, specifically within Hispanic and non-Hispanic Black populations. Additionally, evidence spanning epidemiologic studies that conducted stratified analyses, experimental studies focusing on animal models of disease or individuals with pre-existing disease, dosimetry studies, as well as studies focusing on differential exposure suggest that populations with pre-existing cardiovascular or respiratory disease, populations that are overweight or obese, populations that have particular genetic variants, populations that are of low socioeconomic status, and current/former smokers could be at increased risk for adverse PM_2.5 -related health effects.

3. Nitrogen Oxides

The most recent review of the health effects of oxides of nitrogen completed by EPA can be found in the 2016 Integrated Science Assessment for Oxides of Nitrogen—Health Criteria (Oxides of Nitrogen ISA). The primary source of NO₂ is motor vehicle emissions, and ambient NO₂ concentrations tend to be highly correlated with other traffic-related pollutants. Thus, a key issue in characterizing the causality of NO₂ -health effect relationships consists of evaluating the extent to which studies supported an effect of NO₂ that is independent of other traffic-related pollutants. EPA concluded that the findings for asthma exacerbation integrated from epidemiologic and controlled human exposure studies provided evidence that is sufficient to infer a causal relationship between respiratory effects and short-term NO₂ exposure. The strongest evidence supporting an independent effect of NO₂ exposure comes from controlled human exposure studies demonstrating increased airway responsiveness in individuals with asthma following ambient-relevant NO₂ exposures. The coherence of this evidence with epidemiologic findings for asthma hospital admissions and ED visits as well as lung function decrements and increased pulmonary inflammation in children with asthma describe a plausible pathway by which NO₂ exposure can cause an asthma exacerbation. The 2016 ISA for Oxides of Nitrogen also concluded that there is likely to be a causal relationship between long-term NO₂ exposure and respiratory effects. This conclusion is based on new epidemiologic evidence for associations of NO₂ with asthma development in children combined with biological plausibility from experimental studies.

In evaluating a broader range of health effects, the 2016 ISA for Oxides of Nitrogen concluded that evidence is “suggestive of, but not sufficient to infer, a causal relationship” between short-term NO₂ exposure and cardiovascular effects and mortality and between long-term NO₂ exposure and cardiovascular effects and diabetes, birth outcomes, and cancer. In addition, the scientific evidence is inadequate (insufficient consistency of epidemiologic and toxicological evidence) to infer a causal relationship for long-term NO₂ exposure with fertility, reproduction, and pregnancy, as well as with postnatal development. A key uncertainty in understanding the relationship between these non-respiratory health effects and short- or long-term exposure to NO₂ is copollutant confounding, particularly by other roadway pollutants. The available evidence for non-respiratory health effects does not adequately address whether NO₂ has an independent effect or whether it primarily represents effects related to other or a mixture of traffic-related pollutants.

The 2016 ISA for Oxides of Nitrogen concluded that people with asthma, children, and older adults are at increased risk for NO₂ -related health effects. In these groups and lifestages, NO₂ is consistently related to larger effects on outcomes related to asthma exacerbation, for which there is confidence in the relationship with NO₂ exposure.

4. Carbon Monoxide

Information on the health effects of carbon monoxide (CO) can be found in the January 2010 Integrated Science Assessment for Carbon Monoxide (CO ISA). The CO ISA presents conclusions regarding the presence of causal relationships between CO exposure and categories of adverse health effects. This section provides a summary of the health effects associated with exposure to ambient concentrations of CO, along with the CO ISA conclusions.

Controlled human exposure studies of subjects with coronary artery disease show a decrease in the time to onset of exercise-induced angina (chest pain) and electrocardiogram changes following CO exposure. In addition, epidemiologic studies observed associations between short-term CO exposure and cardiovascular morbidity, particularly increased emergency room visits and hospital admissions for coronary heart disease (including ischemic heart disease, myocardial infarction, and angina). Some epidemiologic evidence is also available for increased hospital admissions and emergency room visits for congestive heart failure and cardiovascular disease as a whole. The CO ISA concludes that a causal relationship is likely to exist between short-term exposures to CO and cardiovascular morbidity. It also concludes that available data are inadequate to conclude that a causal relationship exists between long-term exposures to CO and cardiovascular morbidity.

Animal studies show various neurological effects with in-utero CO exposure. Controlled human exposure studies report central nervous system and behavioral effects following low-level CO exposures, although the findings have not been consistent across all studies. The CO ISA concludes that the evidence is suggestive of a causal relationship with both short- and long-term exposure to CO and central nervous system effects.

A number of studies cited in the CO ISA have evaluated the role of CO exposure in birth outcomes such as preterm birth or cardiac birth defects. There is limited epidemiologic evidence of a CO-induced effect on preterm births and birth defects, with weak evidence for a decrease in birth weight. Animal toxicological studies have found perinatal CO exposure to affect birth weight, as well as other developmental outcomes. The CO ISA concludes that the evidence is suggestive of a causal relationship between long-term exposures to CO and developmental effects and birth outcomes.

Epidemiologic studies provide evidence of associations between short-term CO concentrations and respiratory morbidity such as changes in pulmonary function, respiratory symptoms, and hospital admissions. A limited number of epidemiologic studies considered copollutants such as ozone, SO₂, and PM in two-pollutant models and found that CO risk estimates were generally robust, although this limited evidence makes it difficult to disentangle effects attributed to CO itself from those of the larger complex air pollution mixture. Controlled human exposure studies have not extensively evaluated the effect of CO on respiratory morbidity. Animal studies at levels of 50-100 ppm CO show preliminary evidence of altered pulmonary vascular remodeling and oxidative injury. The CO ISA concludes that the evidence is suggestive of a causal relationship between short-term CO exposure and respiratory morbidity, and inadequate to conclude that a causal relationship exists between long-term exposure and respiratory morbidity.

Finally, the CO ISA concludes that the epidemiologic evidence is suggestive of a causal relationship between short-term concentrations of CO and mortality. Epidemiologic evidence suggests an association exists between short-term exposure to CO and mortality, but limited evidence is available to evaluate cause-specific mortality outcomes associated with CO exposure. In addition, the attenuation of CO risk estimates which was often observed in copollutant models contributes to the uncertainty as to whether CO is acting alone or as an indicator for other combustion-related pollutants. The CO ISA also concludes that there is not likely to be a causal relationship between relevant long-term exposures to CO and mortality.

5. Diesel Exhaust

In EPA's 2002 Diesel Health Assessment Document (Diesel HAD), exposure to diesel exhaust was classified as likely to be carcinogenic to humans by inhalation from environmental exposures, in accordance with the revised draft 1996/1999 EPA cancer guidelines. A number of other agencies (National Institute for Occupational Safety and Health, the International Agency for Research on Cancer, the World Health Organization, California EPA, and the U.S. Department of Health and Human Services) made similar hazard classifications prior to 2002. EPA also concluded in the 2002 Diesel HAD that it was not possible to calculate a cancer unit risk for diesel exhaust due to limitations in the exposure data for the occupational groups or the absence of a dose-response relationship.

In the absence of a cancer unit risk, the Diesel HAD sought to provide additional insight into the significance of the diesel exhaust cancer hazard by estimating possible ranges of risk that might be present in the population. An exploratory analysis was used to characterize a range of possible lung cancer risk. The outcome was that environmental risks of cancer from long-term diesel exhaust exposures could plausibly range from as low as 10⁻⁵ to as high as 10⁻³ . Because of uncertainties, the analysis acknowledged that the risks could be lower than 10⁻⁵, and a zero risk from diesel exhaust exposure could not be ruled out.

Noncancer health effects of acute and chronic exposure to diesel exhaust emissions are also of concern to EPA. EPA derived a diesel exhaust reference concentration (RfC) from consideration of four well-conducted chronic rat inhalation studies showing adverse pulmonary effects. The RfC is 5 µg/m³ for diesel exhaust measured as diesel particulate matter. This RfC does not consider allergenic effects such as those associated with asthma or immunologic or the potential for cardiac effects. There was emerging evidence in 2002, discussed in the Diesel HAD, that exposure to diesel exhaust can exacerbate these effects, but the exposure-response data were lacking at that time to derive an RfC based on these then-emerging considerations. The Diesel HAD states, “With [diesel particulate matter] being a ubiquitous component of ambient PM, there is an uncertainty about the adequacy of the existing [diesel exhaust] noncancer database to identify all of the pertinent [diesel exhaust]-caused noncancer health hazards.” The Diesel HAD also notes “that acute exposure to [diesel exhaust] has been associated with irritation of the eye, nose, and throat, respiratory symptoms (cough and phlegm), and neurophysiological symptoms such as headache, lightheadedness, nausea, vomiting, and numbness or tingling of the extremities.” The Diesel HAD notes that the cancer and noncancer hazard conclusions applied to the general use of diesel engines then on the market and as cleaner engines replace a substantial number of existing ones, the applicability of the conclusions would need to be reevaluated.

It is important to note that the Diesel HAD also briefly summarizes health effects associated with ambient PM and discusses EPA's then-annual PM_2.5 NAAQS of 15 µg/m . In 2012, EPA revised the annual PM_2.5 NAAQS to 12 µg/m and then retained that standard in 2020, as of June 10, 2021 EPA is reconsidering the PM_2.5 NAAQS. There is a large and extensive body of human data showing a wide spectrum of adverse health effects associated with exposure to ambient PM, of which diesel exhaust is an important component. The PM_2.5 NAAQS is designed to provide protection from the noncancer health effects and premature mortality attributed to exposure to PM_2.5 . The contribution of diesel PM to total ambient PM varies in different regions of the country and also, within a region, from one area to another. The contribution can be high in near-roadway environments, for example, or in other locations where diesel engine use is concentrated.

Since 2002, several new studies have been published which continue to report increased lung cancer risk associated with occupational exposure to diesel exhaust from older engines. Of particular note since 2011 are three new epidemiology studies which have examined lung cancer in occupational populations, for example, truck drivers, underground nonmetal miners and other diesel motor-related occupations. These studies reported increased risk of lung cancer with exposure to diesel exhaust with evidence of positive exposure-response relationships to varying degrees. These newer studies (along with others that have appeared in the scientific literature) add to the evidence EPA evaluated in the 2002 Diesel HAD and further reinforce the concern that diesel exhaust exposure likely poses a lung cancer hazard. The findings from these newer studies do not necessarily apply to newer technology diesel engines ( i.e., heavy-duty highway engines from 2007 and later model years) since the newer engines have large reductions in the emission constituents compared to older technology diesel engines.

In light of the growing body of scientific literature evaluating the health effects of exposure to diesel exhaust, in June 2012 the World Health Organization's International Agency for Research on Cancer (IARC), a recognized international authority on the carcinogenic potential of chemicals and other agents, evaluated the full range of cancer-related health effects data for diesel engine exhaust. IARC concluded that diesel exhaust should be regarded as “carcinogenic to humans.” This designation was an update from its 1988 evaluation that considered the evidence to be indicative of a “probable human carcinogen.”

6. Air Toxics

Heavy-duty engine emissions contribute to ambient levels of air toxics that are known or suspected human or animal carcinogens, or that have noncancer health effects. These compounds include, but are not limited to, benzene, formaldehyde, acetaldehyde, and naphthalene. These compounds were identified as national or regional risk drivers or contributors in the 2014 National-scale Air Toxics Assessment and have significant inventory contributions from mobile sources. Chapter 4 of the draft RIA includes additional information on the health effects associated with exposure to each of these pollutants.

7. Exposure and Health Effects Associated With Traffic

Locations in close proximity to major roadways generally have elevated concentrations of many air pollutants emitted from motor vehicles. Hundreds of such studies have been published in peer-reviewed journals, concluding that concentrations of CO, CO₂, NO, NO₂, benzene, aldehydes, particulate matter, black carbon, and many other compounds are elevated in ambient air within approximately 300-600 meters (about 1,000-2,000 feet) of major roadways. The highest concentrations of most pollutants emitted directly by motor vehicles are found at locations within 50 meters (about 165 feet) of the edge of a roadway's traffic lanes.

A large-scale review of air quality measurements in the vicinity of major roadways between 1978 and 2008 concluded that the pollutants with the steepest concentration gradients in vicinities of roadways were CO, ultrafine particles, metals, elemental carbon (EC), NO, NO_X , and several VOCs. These pollutants showed a large reduction in concentrations within 100 meters downwind of the roadway. Pollutants that showed more gradual reductions with distance from roadways included benzene, NO₂, PM_2.5, and PM₁₀ . In the review article, results varied based on the method of statistical analysis used to determine the gradient in concentration. More recent studies continue to show significant concentration gradients of traffic-related air pollution around major roads. There is evidence that EPA's regulations for vehicles have lowered the near-road concentrations and gradients. Starting in 2010, EPA required through the NAAQS process that air quality monitors be placed near high-traffic roadways for determining concentrations of CO, NO₂, and PM_2.5 (in addition to those existing monitors located in neighborhoods and other locations farther away from pollution sources). The monitoring data for NO₂ indicate that in urban areas, monitors near roadways often report the highest concentrations of NO₂ .

For pollutants with relatively high background concentrations relative to near-road concentrations, detecting concentration gradients can be difficult. For example, many aldehydes have high background concentrations as a result of photochemical breakdown of precursors from many different organic compounds. However, several studies have measured aldehydes in multiple weather conditions and found higher concentrations of many carbonyls downwind of roadways. These findings suggest a substantial roadway source of these carbonyls.

In the past 20 years, many studies have been published with results reporting that populations who live, work, or go to school near high-traffic roadways experience higher rates of numerous adverse health effects, compared to populations far away from major roads. In addition, numerous studies have found adverse health effects associated with spending time in traffic, such as commuting or walking along high-traffic roadways. The health outcomes with the strongest evidence linking them with traffic-associated air pollutants are respiratory effects, particularly in asthmatic children, and cardiovascular effects. ANPR commenters stress the importance of consideration of the impacts of traffic-related air pollution on children's health.

Numerous reviews of this body of health literature have been published as well. In 2010, an expert panel of the Health Effects Institute (HEI) published a review of hundreds of exposure, epidemiology, and toxicology studies. The panel rated how the evidence for each type of health outcome supported a conclusion of a causal association with traffic-associated air pollution as either “sufficient,” “suggestive but not sufficient,” or “inadequate and insufficient.” The panel categorized evidence of a causal association for exacerbation of childhood asthma as “sufficient.” The panel categorized evidence of a causal association for new onset asthma as between “sufficient” and “suggestive but not sufficient.” “Suggestive of a causal association” was how the panel categorized evidence linking traffic-associated air pollutants with exacerbation of adult respiratory symptoms and lung function decrement. It categorized as “inadequate and insufficient” evidence of a causal relationship between traffic-related air pollution and health care utilization for respiratory problems, new onset adult asthma, chronic obstructive pulmonary disease (COPD), non-asthmatic respiratory allergy, and cancer in adults and children. Currently, HEI is conducting another expert review of health studies associated with traffic-related air pollution published after the studies included in their 2010 review. Other literature reviews have been published with conclusions generally similar to the 2010 HEI panel's. However, in 2014, researchers from the U.S. Centers for Disease Control and Prevention (CDC) published a systematic review and meta-analysis of studies evaluating the risk of childhood leukemia associated with traffic exposure and reported positive associations between “postnatal” proximity to traffic and leukemia risks, but no such association for “prenatal” exposures. The U.S. Department of Health and Human Services' National Toxicology Program (NTP) recently published a monograph including a systematic review of traffic-related air pollution (TRAP) and its impacts on hypertensive disorders of pregnancy. NTP concluded that exposure to TRAP is “presumed to be a hazard to pregnant women” for developing hypertensive disorders of pregnancy.

Health outcomes with few publications suggest the possibility of other effects still lacking sufficient evidence to draw definitive conclusions. Among these outcomes with a small number of positive studies are neurological impacts ( e.g., autism and reduced cognitive function) and reproductive outcomes ( e.g., preterm birth, low birth weight).

In addition to health outcomes, particularly cardiopulmonary effects, conclusions of numerous studies suggest mechanisms by which traffic-related air pollution affects health. Numerous studies indicate that near-roadway exposures may increase systemic inflammation, affecting organ systems,

including blood vessels and lungs. Long-term exposures in near-road environments have been associated with inflammation-associated conditions, such as atherosclerosis and asthma.

Several studies suggest that some factors may increase susceptibility to the effects of traffic-associated air pollution. Several studies have found stronger respiratory associations in children experiencing chronic social stress, such as in violent neighborhoods or in homes with high family stress.

The risks associated with residence, workplace, or schools near major roads are of potentially high public health significance due to the large population in such locations. Every two years from 1997 to 2009 and in 2011, the U.S. Census Bureau's American Housing Survey (AHS) conducted a survey that includes whether housing units are within 300 feet of an “airport, railroad, or highway with four or more lanes.” The 2013 AHS was the last AHS that included that question. The 2013 survey reports that 17.3 million housing units, or 13 percent of all housing units in the U.S., were in such areas. Assuming that populations and housing units are in the same locations, this corresponds to a population of more than 41 million U.S. residents in close proximity to high-traffic roadways or other transportation sources. According to the Central Intelligence Agency's World Factbook, based on data collected between 2012-2014, the United States had 6,586,610 km of roadways, 293,564 km of railways, and 13,513 airports. As such, highways represent the overwhelming majority of transportation facilities described by this factor in the AHS.

EPA also conducted a recent study to estimate the number of people living near truck freight routes in the United States. Based on a population analysis using the U.S. Department of Transportation's (USDOT) Freight Analysis Framework 4 (FAF4) and population data from the 2010 decennial census, an estimated 72 million people live within 200 meters of these freight routes. In addition, relative to the rest of the population, people of color and those with lower incomes are more likely to live near FAF4 truck routes. They are also more likely to live in metropolitan areas. Past work has also shown that, on average, Americans spend more than an hour traveling each day, bringing nearly all residents into a high-exposure microenvironment for part of the day.

8. Environmental Justice

Executive Order 12898 (59 FR 7629, February 16, 1994) establishes federal executive policy on environmental justice. It directs federal agencies, to the greatest extent practicable and permitted by law, to make achieving environmental justice part of their mission by identifying and addressing, as appropriate, disproportionately high and adverse human health or environmental effects of their programs, policies, and activities on minority populations and low-income populations in the United States. EPA defines environmental justice as the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies.

Executive Order 14008 (86 FR 7619, February 1, 2021) also calls on federal agencies to make achieving environmental justice part of their respective missions “by developing programs, policies, and activities to address the disproportionately high and adverse human health, environmental, climate-related and other cumulative impacts on disadvantaged communities, as well as the accompanying economic challenges of such impacts.” It declares a policy “to secure environmental justice and spur economic opportunity for disadvantaged communities that have been historically marginalized and overburdened by pollution and under-investment in housing, transportation, water and wastewater infrastructure and health care.”

Under Executive Order 13563 (76 FR 3821, January 18, 2011), federal agencies may consider equity, human dignity, fairness, and distributional considerations in their regulatory analyses, where appropriate and permitted by law.

EPA's 2016 “Technical Guidance for Assessing Environmental Justice in Regulatory Analysis” provides recommendations on conducting the highest quality analysis feasible, recognizing that data limitations, time and resource constraints, and analytic challenges will vary by media and regulatory context. When assessing the potential for disproportionately high and adverse health or environmental impacts of regulatory actions on minority populations, low-income populations, Tribes, and/or indigenous peoples, the EPA strives to answer three broad questions: (1) Is there evidence of potential environmental justice (EJ) concerns in the baseline (the state of the world absent the regulatory action)? Assessing the baseline will allow the EPA to determine whether pre-existing disparities are associated with the pollutant(s) under consideration ( e.g., if the effects of the pollutant(s) are more concentrated in some population groups). (2) Is there evidence of potential EJ concerns for the regulatory option(s) under consideration? Specifically, how are the pollutant(s) and its effects distributed for the regulatory options under consideration? And, (3) do the regulatory option(s) under consideration exacerbate or mitigate EJ concerns relative to the baseline? It is not always possible to quantitatively assess these questions.

EPA's 2016 Technical Guidance does not prescribe or recommend a specific approach or methodology for conducting an environmental justice analysis, though a key consideration is consistency with the assumptions underlying other parts of the regulatory analysis when evaluating the baseline and regulatory options. Where applicable and practicable, the Agency endeavors to conduct such an analysis. EPA is committed to conducting environmental justice analysis for rulemakings based on a framework similar to what is outlined in EPA's Technical Guidance, in addition to investigating ways to further weave environmental justice into the fabric of the rulemaking process.

EPA seeks to ensure that no group of people faces a disproportionate burden of exposure to mobile-source pollution. In general, we expect reduced tailpipe emissions of NO_X from heavy-duty diesel engines and reduced tailpipe emissions of NO_X, CO, PM, and VOCs from heavy-duty gasoline engines. See Section VI.B for more detail on the emissions reductions from this proposal.

There is evidence that communities with EJ concerns are disproportionately impacted by the emissions associated with this proposal. Numerous studies have found that environmental hazards such as air pollution are more prevalent in areas where people of color and low-income populations represent a higher fraction of the population compared with the general population. Consistent with this evidence, a recent study found that most anthropogenic sources of PM_2.5 , including industrial sources and light- and heavy-duty vehicle sources, disproportionately affect people of color. In addition, compared to non-Hispanic Whites, some minorities experience greater levels of health problems during some life stages. For example, in 2017-2019, about 14 percent of Black, non-Hispanic and 8 percent of Hispanic children were estimated to currently have asthma, compared with 6 percent of White, non-Hispanic children.

As discussed in Section II.B.7 of this document, concentrations of many air pollutants are elevated near high-traffic roadways. In addition, numerous state and local commenters on the ANPR noted that truck trips frequently start and end around goods movement facilities including marine ports and warehouses, making consideration of truck emissions an important element of addressing air quality experienced by populations living near those facilities.

We conducted an analysis of the populations living in close proximity to truck freight routes as identified in USDOT's Freight Analysis Framework 4 (FAF4). FAF4 is a model from the USDOT's Bureau of Transportation Statistics (BTS) and Federal Highway Administration (FHWA), which provides data associated with freight movement in the U.S. Relative to the rest of the population, people living near FAF4 truck routes are more likely to be people of color and have lower incomes than the general population. People living near FAF4 truck routes are also more likely to live in metropolitan areas. Even controlling for region of the country, county characteristics, population density, and household structure, race, ethnicity, and income are significant determinants of whether someone lives near a FAF4 truck route.

We also reviewed existing scholarly literature examining the potential for disproportionate exposure among people of color and people with low socioeconomic status (SES), and we conducted our own evaluation of two national datasets: The U.S. Census Bureau's American Housing Survey for calendar year 2009 and the U.S. Department of Education's database of school locations. Numerous studies evaluating the demographics and socioeconomic status of populations or schools near roadways have found that they include a greater percentage of residents of color, as well as lower SES populations (as indicated by variables such as median household income). Locations in these studies include Los Angeles, CA; Seattle, WA; Wayne County, MI; Orange County, FL; and the

State of California. Such disparities may be due to multiple factors.

People with low SES often live in neighborhoods with multiple stressors and health risk factors, including reduced health insurance coverage rates, higher smoking and drug use rates, limited access to fresh food, visible neighborhood violence, and elevated rates of obesity and some diseases such as asthma, diabetes, and ischemic heart disease. Although questions remain, several studies find stronger associations between air pollution and health in locations with such chronic neighborhood stress, suggesting that populations in these areas may be more susceptible to the effects of air pollution.

Several publications report nationwide analyses that compare the demographic patterns of people who do or do not live near major roadways. Three of these studies found that people living near major roadways are more likely to be minorities or low in SES. They also found that the outcomes of their analyses varied between regions within the U.S. However, only one such study looked at whether such conclusions were confounded by living in a location with higher population density and how demographics differ between locations nationwide. In general, it found that higher density areas have higher proportions of low-income residents and people of color. In other publications based on a city, county, or state, the results are similar.

We analyzed two national databases that allowed us to evaluate whether homes and schools were located near a major road and whether disparities in exposure may be occurring in these environments. The American Housing Survey (AHS) includes descriptive statistics of over 70,000 housing units across the nation. The survey is conducted every two years by the U.S. Census Bureau. The second database we analyzed was the U.S. Department of Education's Common Core of Data, which includes enrollment and location information for schools across the U.S.

In analyzing the 2009 AHS, we focused on whether a housing unit was located within 300 feet, the distance provided in the AHS data, of a “4-or-more lane highway, railroad, or airport.” We analyzed whether there were differences between households in such locations compared with those in locations farther from these transportation facilities. We included other variables, such as land use category, region of country, and housing type. We found that homes with a non-White householder were 22-34 percent more likely to be located within 300 feet of these large transportation facilities than homes with White householders. Homes with a Hispanic householder were 17-33 percent more likely to be located within 300 feet of these large transportation facilities than homes with non-Hispanic householders. Households near large transportation facilities were, on average, lower in income and educational attainment and more likely to be a rental property and located in an urban area compared with households more distant from transportation facilities.

In examining schools near major roadways, we examined the Common Core of Data (CCD) from the U.S. Department of Education, which includes information on all public elementary and secondary schools and school districts nationwide. To determine school proximities to major roadways, we used a geographic information system (GIS) to map each school and roadways based on the U.S. Census's TIGER roadway file. We found that students of color were overrepresented at schools within 200 meters of the largest roadways, and schools within 200 meters of the largest roadways had higher than expected numbers of students eligible for free or reduced-price lunches. For example, Black students represent 22 percent of students at schools located within 200 meters of a primary road, compared to 17 percent of students in all U.S. schools. Hispanic students represent 30 percent of students at schools located within 200 meters of a primary road, compared to 22 percent of students in all U.S. schools.

Overall, there is substantial evidence that people who live or attend school near major roadways are more likely to be of a non-White race, Hispanic, and/or have a low SES. Although proximity to an emissions source is an indicator of potential exposure, it is important to note that the impacts of emissions from tailpipe sources are not limited to communities in close proximity to these sources. For example, the effects of potential decreases in emissions from sources that would be affected by this proposal might also be felt many miles away, including in communities with EJ concerns. The spatial extent of these impacts depends on a range of interacting and complex factors including the amount of pollutant emitted, atmospheric lifetime of the pollutant, terrain, atmospheric chemistry and meteorology.

We also conducted an analysis of how the air quality impacts from this proposed rule would be distributed among different populations, specifically focusing on PM_2.5 and ozone concentrations in the contiguous U.S. This analysis assessed whether areas with the worst projected baseline air quality in 2045 have larger numbers of people of color living in them, and if those with the worst projected air quality would benefit more from the proposed rule. We found that in the 2045 baseline, nearly double the number of people of color live within areas with the worst air quality, compared to non-Hispanic Whites (NH-Whites). We also found that the largest improvements in both ozone and PM_2.5 are estimated to occur in these areas with the worst baseline air quality. See Section VII.H for additional information on the demographic analysis.

In summary, we expect this proposed rule would result in reductions of emissions that contribute to ozone, PM_2.5, and other harmful pollution. The emission reductions from this proposed rule would result in widespread air quality improvements, including in the areas with the worst baseline air quality, where a larger number of people of color are projected to reside.

C. Environmental Effects Associated With Exposure to Pollutants Impacted by This Proposal

This section discusses the environmental effects associated with pollutants affected by this proposed rule, specifically particulate matter, ozone, NO_X and air toxics.

1. Visibility

Visibility can be defined as the degree to which the atmosphere is transparent to visible light. Visibility impairment is caused by light scattering and absorption by suspended particles and gases. It is dominated by contributions from suspended particles except under pristine conditions. Visibility is important because it has direct significance to people's enjoyment of daily activities in all parts of the country. Individuals value good visibility for the well-being it provides them directly, where they live and work, and in places where they enjoy recreational opportunities. Visibility is also highly valued in significant natural areas, such as national parks and wilderness areas, and special emphasis is given to protecting visibility in these areas. For more information on visibility see the final 2019 PM ISA.

EPA is working to address visibility impairment. Reductions in air pollution from implementation of various programs associated with the Clean Air Act Amendments of 1990 provisions have resulted in substantial improvements in visibility and will continue to do so in the future. Because trends in haze are closely associated with trends in particulate sulfate and nitrate due to the relationship between their concentration and light extinction, visibility trends have improved as emissions of SO₂ and NO_X have decreased over time due to air pollution regulations such as the Acid Rain Program.

In the Clean Air Act Amendments of 1977, Congress recognized visibility's value to society by establishing a national goal to protect national parks and wilderness areas from visibility impairment caused by manmade pollution. In 1999, EPA finalized the regional haze program to protect the visibility in Mandatory Class I Federal areas. There are 156 national parks, forests and wilderness areas categorized as Mandatory Class I Federal areas. These areas are defined in CAA section 162 as those national parks exceeding 6,000 acres, wilderness areas and memorial parks exceeding 5,000 acres, and all international parks which were in existence on August 7, 1977.

EPA has also concluded that PM_2.5 causes adverse effects on visibility in other areas that are not targeted by the Regional Haze Rule, such as urban areas, depending on PM_2.5 concentrations and other factors such as dry chemical composition and relative humidity ( i.e., an indicator of the water composition of the particles). EPA revised the PM_2.5 NAAQS in 2012, retained it in 2020, and established a target level of protection that is expected to be met through attainment of the existing secondary standards for PM_2.5 .

2. Plant and Ecosystem Effects of Ozone

The welfare effects of ozone include effects on ecosystems, which can be observed across a variety of scales, i.e., subcellular, cellular, leaf, whole plant, population and ecosystem. Ozone effects that begin at small spatial scales, such as the leaf of an individual plant, when they occur at sufficient magnitudes (or to a sufficient degree) can result in effects being propagated along a continuum to higher and higher levels of biological organization. For example, effects at the individual plant level, such as altered rates of leaf gas exchange, growth and reproduction, can, when widespread, result in broad changes in ecosystems, such as productivity, carbon storage, water cycling, nutrient cycling, and community composition.

Ozone can produce both acute and chronic injury in sensitive plant species depending on the concentration level and the duration of the exposure. In those sensitive species, effects from repeated exposure to ozone throughout the growing season of the plant can tend to accumulate, so that even relatively low concentrations experienced for a longer duration have the potential to create chronic stress on vegetation. Ozone damage to sensitive plant species includes impaired photosynthesis and visible injury to leaves. The impairment of photosynthesis, the process by which the plant makes carbohydrates (its source of energy and food), can lead to reduced crop yields, timber production, and plant productivity and growth. Impaired photosynthesis can also lead to a reduction in root growth and carbohydrate storage below ground, resulting in other, more subtle plant and ecosystems impacts. These latter impacts include increased susceptibility of plants to insect attack, disease, harsh weather, interspecies competition and overall decreased plant vigor. The adverse effects of ozone on areas with sensitive species could potentially lead to species shifts and loss from the affected ecosystems, resulting in a loss or reduction in associated ecosystem goods and services. Additionally, visible ozone injury to leaves can result in a loss of aesthetic value in areas of special scenic significance like national parks and wilderness areas and reduced use of sensitive ornamentals in landscaping. In addition to ozone effects on vegetation, newer evidence suggests that ozone affects interactions between plants and insects by altering chemical signals ( e.g., floral scents) that plants use to communicate to other community members, such as attraction of pollinators.

The Ozone ISA presents more detailed information on how ozone affects vegetation and ecosystems. The Ozone ISA reports causal and likely causal relationships between ozone exposure and a number of welfare effects and characterizes the weight of evidence for different effects associated with ozone. The ISA concludes that visible foliar injury effects on vegetation, reduced vegetation growth, reduced plant reproduction, reduced productivity in terrestrial ecosystems, reduced yield and quality of agricultural crops, alteration of below-ground biogeochemical cycles, and altered terrestrial community composition are causally associated with exposure to ozone. It also concludes that increased tree mortality, altered herbivore growth and reproduction, altered plant-insect signaling, reduced carbon sequestration in terrestrial ecosystems, and alteration of terrestrial ecosystem water cycling are likely to be causally associated with exposure to ozone.

3. Atmospheric Deposition

The Integrated Science Assessment for Oxides of Nitrogen, Oxides of Sulfur, and Particulate Matter—Ecological Criteria documents the ecological effects of the deposition of these criteria air pollutants. It is clear from the body of evidence that oxides of nitrogen, oxides of sulfur, and particulate matter contribute to total nitrogen (N) and sulfur (S) deposition. In turn, N and S deposition cause either nutrient enrichment or acidification depending on the sensitivity of the landscape or the species in question. Both enrichment and acidification are characterized by an alteration of the biogeochemistry and the physiology of organisms, resulting in harmful declines in biodiversity in terrestrial, freshwater, wetland, and estuarine ecosystems in the U.S. Decreases in biodiversity mean that some species become relatively less abundant and may be locally extirpated. In addition to the loss of unique living species, the decline in total biodiversity can be harmful because biodiversity is an important determinant of the stability of ecosystems and their ability to provide socially valuable ecosystem services.

Terrestrial, wetland, freshwater, and estuarine ecosystems in the U.S. are affected by N enrichment/eutrophication caused by N deposition. These effects have been consistently documented across the U.S. for hundreds of species. In aquatic systems increased nitrogen can alter species assemblages and cause eutrophication. In terrestrial systems nitrogen loading can lead to loss of nitrogen-sensitive lichen species, decreased biodiversity of grasslands, meadows and other sensitive habitats, and increased potential for invasive species. For a broader explanation of the topics treated here, refer to the description in Chapter 4 of the draft RIA.

The sensitivity of terrestrial and aquatic ecosystems to acidification from nitrogen and sulfur deposition is predominantly governed by geology. Prolonged exposure to excess nitrogen and sulfur deposition in sensitive areas acidifies lakes, rivers, and soils. Increased acidity in surface waters creates inhospitable conditions for biota and affects the abundance and biodiversity of fishes, zooplankton and macroinvertebrates and ecosystem function. Over time, acidifying deposition also removes essential nutrients from forest soils, depleting the capacity of soils to neutralize future acid loadings and negatively affecting forest sustainability. Major effects in forests include a decline in sensitive tree species, such as red spruce (Picea rubens) and sugar maple (Acer saccharum).

Building materials including metals, stones, cements, and paints undergo natural weathering processes from exposure to environmental elements ( e.g., wind, moisture, temperature fluctuations, sunlight, etc.). Pollution can worsen and accelerate these effects. Deposition of PM is associated with both physical damage (materials damage effects) and impaired aesthetic qualities (soiling effects). Wet and dry deposition of PM can physically affect materials, adding to the effects of natural weathering processes, by potentially promoting or accelerating the corrosion of metals, by degrading paints and by deteriorating building materials such as stone, concrete and marble. The effects of PM are exacerbated by the presence of acidic gases and can be additive or synergistic due to the complex mixture of pollutants in the air and surface characteristics of the material. Acidic deposition has been shown to have an effect on materials including zinc/galvanized steel and other metal, carbonate stone (as monuments and building facings), and surface coatings (paints). The effects on historic buildings and outdoor works of art are of particular concern because of the uniqueness and irreplaceability of many of these objects. In addition to aesthetic and functional effects on metals, stone and glass, altered energy efficiency of photovoltaic panels by PM deposition is also becoming an important consideration for impacts of air pollutants on materials.

4. Environmental Effects of Air Toxics

Emissions from producing, transporting and combusting fuel contribute to ambient levels of pollutants that contribute to adverse effects on vegetation. Volatile organic compounds (VOCs), some of which are considered air toxics, have long been suspected to play a role in vegetation damage. In laboratory experiments, a wide range of tolerance to VOCs has been observed. Decreases in harvested seed pod weight have been reported for the more sensitive plants, and some studies have reported effects on seed germination, flowering and fruit ripening. Effects of individual VOCs or their role in conjunction with other stressors ( e.g., acidification, drought, temperature extremes) have not been well studied. In a recent study of a mixture of VOCs including ethanol and toluene on herbaceous plants, significant effects on seed production, leaf water content and photosynthetic efficiency were reported for some plant species.

Research suggests an adverse impact of vehicle exhaust on plants, which has in some cases been attributed to aromatic compounds and in other cases to nitrogen oxides. The impacts of VOCs on plant reproduction may have long-term implications for biodiversity and survival of native species near major roadways. Most of the studies of the impacts of VOCs on vegetation have focused on short-term exposure and few studies have focused on long-term effects of VOCs on vegetation and the potential for metabolites of these compounds to affect herbivores or insects.

III. Proposed Test Procedures and Standards

In applying heavy-duty criteria pollutant emission standards, EPA divides engines primarily into two types: Compression ignition (CI) (primarily diesel-fueled engines) and spark-ignition (SI) (primarily gasoline-fueled engines). The CI standards and requirements also apply to the largest natural gas engines. Battery-electric and fuel-cell vehicles are also subject to criteria pollutant standards and requirements. All heavy-duty highway engines are subject to brake-specific (g/hp-hr) exhaust emission standards for four criteria pollutants: Oxides of nitrogen (NO_X ), particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO). In this section we describe two regulatory options for new emissions standards: Proposed Option 1 and proposed Option 2 and updates we are proposing to the test procedures that apply for these pollutants. Unless explicitly stated otherwise, the proposed provisions in this section and Section IV would apply to proposed Options 1 and 2, as well as the full range of options in between them.

A. Overview

In the following section, we provide an overview of our proposal to migrate and update our criteria pollutant regulations for model year 2027 and later heavy-duty highway engines, our proposed Options 1 and 2 standards and test procedures, and our analysis demonstrating the feasibility of the proposed standards. The sections that follow provide more detail on each of these topics. Section III.B and Section III.D include the proposed changes to our laboratory-based standards and test procedures for heavy-duty compression-ignition and spark-ignition engines, respectively. Section III.C introduces our proposed off-cycle standards and test procedures that extend beyond the laboratory to on-the-road, real-world conditions. Section III.E describes our proposal for new refueling standards for certain heavy-duty spark-ignition engines. Each of these sections include descriptions of the current standards and test procedures and our proposed updates, including our feasibility demonstrations and the data we relied on to support our proposals.

1. Migration and Clarifications of Regulatory Text

As noted in Section I of this preamble, we are proposing to migrate our criteria pollutant regulations for model year 2027 and later heavy-duty highway engines from their current location in 40 CFR part 86, subpart A, to 40 CFR part 1036. Consistent with this migration, the proposed compliance provisions discussed in this section refer to the proposed regulations in their new location in part 1036. In general, this migration is not intended to change the compliance program previously specified in part 86, except as specifically proposed in this rulemaking. See our memorandum to the docket for a detailed description of the proposed migration. The proposal includes updating cross references to 40 CFR parts 86 and 1036 in several places to properly cite the new rulemaking provisions in this rule.

i. Compression- and Spark-Ignition Engines Regulatory Text

For many years, the regulations of 40 CFR part 86 have referred to “diesel heavy-duty engines” and “Otto-cycle heavy-duty engines”; however, as we migrate the heavy-duty provisions of 40 CFR part 86, subpart A, to 40 CFR part 1036 in this proposal, we refer to these engines as “compression-ignition” (CI) and “spark-ignition” (SI), respectively, which are more comprehensive terms and consistent with existing language in 40 CFR part 1037 for heavy-duty motor vehicle regulations. In this section, and throughout the preamble, reference to diesel and Otto-cycle engines is generally limited to discussions relating to current test procedures and specific terminology used in 40 CFR part 86. We are also proposing to update the terminology for the primary intended service classes in 40 CFR 1036.140 to replace Heavy heavy-duty engine with Heavy HDE, Medium heavy-duty engine with Medium HDE, Light heavy-duty engine with Light HDE, and Spark-ignition heavy-duty engine with Spark-ignition HDE. Our proposal includes revisions throughout 40 CFR parts 1036 and 1037 to reflect this updated terminology.

ii. Heavy-Duty Hybrid Regulatory Text

Similar to our updates to more comprehensive and consistent terminology for CI and SI engines, as part of this proposal we are also updating and clarifying regulatory language for hybrid engines and hybrid powertrains. We propose to update the definition of “engine configuration” in 40 CFR 1036.801 to clarify that an engine configuration would include hybrid components if it is certified as a hybrid engine or hybrid powertrain. We are proposing first to clarify in 40 CFR 1036.101(b) that regulatory references in part 1036 to engines generally apply to hybrid engines and hybrid powertrains. We are also proposing to clarify in 40 CFR 1036.101(b) that manufacturers may optionally test the hybrid engine and powertrain together, rather than testing the engine alone; this option would allow manufacturers to demonstrate emission performance of the hybrid technology that are not apparent when testing the engine alone.

To certify a hybrid engine or hybrid powertrain to criteria pollutant standards, we propose that manufacturers would declare a primary intended service class of the engine configuration using the proposed updated 40 CFR 1036.140. The current provisions of 40 CFR 1036.140 distinguish classes based on engine characteristics and characteristics of the vehicles for which manufacturers intend to design and market their engines. Under this proposal, manufacturers certifying hybrid engines and hybrid powertrains would use good engineering judgment to identify the class that best describes their engine configuration. Once a primary intended service class is declared, the engine configuration would be subject to all the criteria pollutant emission standards and related compliance provisions for that class.

We propose to update 40 CFR 1036.230(c) to include hybrid powertrains and are proposing that engine configurations certified as hybrid engine or hybrid powertrain may not be included in an engine family with conventional engines, consistent with the current provisions. We note that this provision would result in more engine families for manufacturers certifying hybrids. We request comment on our proposed clarification in 40 CFR 1036.101(b) that manufacturers may optionally test the hybrid engine and powertrain together, rather than testing the engine alone. Specifically, we are interested in stakeholder input on whether EPA should require all hybrid engines and powertrains to be certified together, rather than making it optional. We are interested in commenters' views on the impact of additional engine/powertrain families if we were to require powertrain testing for all hybrid engine and powertrain engine configurations, including a manufacturers' ability to conduct certification testing and any recommended steps EPA should take to address such effects. We are also interested in commenters' views on whether the powertrain test always provides test results that are more representative of hybrid emission performance in the real world, or if for some hybrid systems the engine test procedure provides equally or more representative results. For instance, we solicit comment on whether for some hybrids, such as mild-hybrids, the powertrain test should continue to be an option, even if we were to require that all other hybrids must use the powertrain test.

We are also interested in stakeholder input on potential alternative approaches, such as if EPA were to add new, separate service classes for hybrid engines and powertrains in the final rule. Distinct service classes for hybrid engines and powertrains could allow EPA to consider separate emission standards, useful life, and/or test procedures for hybrids based on unique performance attributes; however, it could also add burden to EPA and manufacturers by creating additional categories to track and maintain. We request that commenters suggesting separate primary intended service classes for hybrid engines and powertrains include data, if possible, to support an analysis of appropriate corresponding emission standards, useful life periods, and other compliance requirements.

iii. Heavy-Duty Electric Vehicles Regulatory Text

Similar to our updates to more comprehensive and consistent terminology, as part of this proposal we are also updating and consolidating regulatory language for battery-electric vehicles and fuel cell electric vehicles (BEVs and FCEVs). For BEVs and FCEVs, we are proposing to consolidate and update our regulations as part of a migration of heavy-duty vehicle regulations from 40 CFR part 86 to 40 CFR part 1037. In the GHG Phase 1 rulemaking, EPA revised the heavy-duty vehicle and engine regulations to make them consistent with our regulatory approach to electric vehicles (EVs) under the light-duty vehicle program. Specifically, we applied standards for all regulated criteria pollutants and GHGs to all heavy-duty vehicle types, including EVs. Starting in MY 2016, criteria pollutant standards and requirements applicable to heavy-duty vehicles at or below 14,000 pounds GVWR in 40 CFR part 86, subpart S, applied to heavy-duty EVs above 14,000 pounds GVWR through the use of good engineering judgment (see current 40 CFR 86.016-1(d)(4)). Under the current 40 CFR 86.016-1(d)(4), heavy-duty vehicles powered solely by electricity are deemed to have zero emissions of regulated pollutants; this provision also provides that heavy-duty EVs may not generate NO_X or PM emission credits. Additionally, part 1037 applies to heavy-duty EVs above 14,000 pounds GVWR (see current 40 CFR 1037.1).

In this rulemaking, we are proposing to consolidate certification requirements for BEVs and FCEVs over 14,000 pounds GVWR in 40 CFR part 1037 such that manufacturers of BEVs and FCEVs over 14,000 pounds GVWR would certify to meeting the emission standards and requirements of part 1037, as provided in the current 40 CFR 1037.1. In the proposed 40 CFR 1037.102(b), we clarify that BEVs and FCEVs are subject to criteria pollutant standards as follows: Prior to MY 2027, the emission standards under the current 40 CFR 86.007-11 would apply, while the emission standards under the proposed 40 CFR 1036.104 would apply starting in MY 2027. As specified in the proposed 40 CFR 1037.205(q), starting in MY 2027, BEV and FCEV manufacturers could choose to attest that vehicles comply with the standards of 40 CFR 1037.102 instead of submitting test data. As discussed in Section IV.I, we are proposing in 40 CFR 1037.616 that, starting in MY 2024, manufacturers may choose to generate NO_X emission credits from BEVs and FCEVs if the vehicle meets durability requirements described in proposed 40 CFR 1037.102(b)(3). Manufacturers choosing to generate NO_X emission credits under proposed 40 CFR 1037.616 may attest to meeting durability requirements while also submitting test results required for calculating NO_X emission credits and quantifying initial battery or fuel cell performance. We are proposing to continue to not to allow heavy-duty EVs to generate PM emission credits since we are proposing not to allow any manufacturer to generate PM emission credits for use in MY 2027 and later under the proposed averaging, banking, and trading program presented in Section IV.G.

2. Proposed Numeric Standards and Test Procedures for Compression-Ignition and Spark-Ignition Engines

EPA is proposing new NO_X, PM, HC, and CO emission standards for heavy-duty engines that will be certified under 40 CFR part 1036. As noted in the introduction to this preamble, the highway heavy-duty vehicle market is largely segmented in that a majority of the lightest weight class vehicles are powered by gasoline-fueled spark-ignition engines and most of the heaviest weight class vehicles are powered by diesel-fueled compression-ignition engines. There is significant overlap in the engines installed in Class 4-6 applications. Considering the interchangeable nature of these middle range vehicles, we have designed our proposed program options so that, regardless of what the market chooses ( e.g., gasoline- or diesel-fueled engines), similar emission reductions would be realized over their expected operational lives. We believe it is appropriate to propose standards that are numerically fuel neutral yet account for the fundamental differences between CI and SI engines. We believe this proposed approach would result in roughly equivalent implementation burdens for manufacturers. As described in this section, the proposed Options 1 and 2 NO_X and PM standards are based on test data from our CI engine feasibility demonstration program. We also find that they are feasible for SI engines based on currently available technologies and we are adopting them for SI engines to maintain fuel neutral standards. The proposed Options 1 and 2 HC and CO standards are based on HD SI engine emission performance. We also find that they are feasible for CI engines based on currently available technologies and we are adopting them for CI engines to maintain fuel neutral standards. We have not relied on the use of HEV, BEV, or FCEV technologies in the development of our proposed Options 1 and 2 or the Alternative standards; however, as discussed in Section IV, we are proposing to allow these technologies to generate NO_X emission credits as a flexibility for manufacturers to spread out their investment and prioritize technology adoption to the applications that make the most sense for their businesses during their transition to meeting the proposed more stringent standards (see Sections IV.G, IV.H, and, IV.I for details on our proposed approach to NO_X emission credits). We do not expect that current market penetration of BEVs (0.06 percent in MY 2019) or projected penetration rate in the MY 2027 timeframe (1.5 percent) would meaningfully impact our analysis for developing the numeric level of the proposed Options 1 and 2 standards; however, as noted in III.B.5, we are requesting comment on whether to include HEV, BEV, and/or FCEV technologies in our feasibility analysis for the final rule and may re-evaluate our approach, especially if we receive information showing higher BEV/FCEV market penetration in the MY 2027 or later timeframe.

Engine manufacturers historically have demonstrated compliance with EPA emission standards by measuring emissions while the engine is operating over precisely defined duty cycles in an emissions testing laboratory. The primary advantage of this approach is that it provides very repeatable emission measurements. In other words, the results should be the same no matter when or where the test is performed, as long as the specified test procedures are used. We continue to consider pre-production laboratory engine testing (and durability demonstrations) as the cornerstone of ensuring in-use emission standards compliance. However, tying each emission standard to a specific, defined test cycle leaves open the possibility of emission controls being designed more to the limited conditions of the test procedures than to the full range of in-use operation. Since 2004, we have applied additional off-cycle standards for diesel engines that allow higher emission levels but are not limited to a specific duty cycle, and instead measure emissions over real-world, non-prescribed driving routes that cover a range of in-use operation. Our proposal includes new and updated heavy-duty engine test procedures and standards, both for duty cycle standards to be tested in an emissions testing laboratory and for off-cycle standards that can be tested on the road in real-world conditions, as described in the following sections.

3. Implementation of Proposed Program

As discussed in this section, we have evaluated the proposed standards in terms of technological feasibility, lead time, stability, cost, energy, and safety, consistent with the requirements in CAA section 202(a)(3). We are proposing standards based on our CI and SI engine feasibility demonstration programs, with Option 1 standards in two steps for MY 2027 and MY 2031 and Option 2 standards in one step starting in MY 2027. Our evaluation of available data shows that the standards and useful life periods in both steps of proposed Option 1 are feasible and would result in the greatest emission reductions achievable for the model years to which they are proposed to apply, pursuant to CAA section 202(a)(3), giving appropriate consideration to cost, lead time, and other factors. Our analysis further shows that the standards and useful life periods in proposed Option 2 are feasible in the 2027 model year, but would result in lower levels of emission reductions compared to proposed Option 1. As explained further in this section and Chapter 3 of the draft RIA, we expect that additional data from EPA's ongoing work to demonstrate the performance of emission control technologies, as well as information received in public comments, will allow us to refine our assessments and consideration of the feasibility of the combination of the standards and useful life periods, particularly for the largest CI engines (HHDEs), in proposed Options 1 and 2, after consideration of lead time, costs, and other factors. Therefore, we are co-proposing Options 1 and 2 standards and useful life periods, and the range of options in between them, as the options that may potentially be appropriate to finalize pursuant to CAA section 202(a)(3) once EPA has considered that additional data and other information.

We are proposing MY 2027 as the first implementation year for both options to align with the final step of the HD GHG Phase 2 standards, which would provide at least four years of lead time from a final rulemaking in 2022. As discussed in Section I and detailed in this section, the four-year lead time for the proposed criteria pollutant standards allows manufacturers to develop and apply the emission control technologies needed to meet the proposed standards, and to ensure those technologies will be durable for the proposed longer useful life periods; four years of lead time is also consistent with the CAA requirements.

In the event that manufacturers start production of some engine families sooner than four years from our final rule, we are proposing an option to split the 2027 model year. Specifically, we are proposing that a MY 2027 engine family that starts production within four years of the final rule could comply with the proposed MY 2027 standards for all engines produced for that engine family in MY2027 or could split the engine family by production date in MY 2027 such that engines in the family produced prior to four years after the final rule would continue to be subject to the existing standards. This proposed option to split the first model year provides assurance that all manufacturers, regardless of when they start production of their engine families, will have four years of lead time to the proposed first implementation step in MY 2027.

For Option 1, the phased implementation would also provide four years of stability before increasing stringency again in MY 2031. Through comments received on our ANPR, we have heard from manufacturers that given the challenge of implementing the third step of the HD GHG rules in MY 2027, they believe it would take closer to four years to adequately fine-tune and validate their products for a second step of more stringent criteria pollutant control that also extends useful life. In response to this concern, and the general request by suppliers and environmental stakeholders for a nationally aligned criteria pollutant program, we are proposing MY 2031 for the final step of the proposed Option 1 standards to provide four additional years for manufacturers to design and build engines that will meet the proposed second step of the Option 1 standards and associated compliance provisions. A MY 2031 final step would also align with the Omnibus. We request comment on the general approach of a two-step versus one-step program, and the advantages or disadvantages of the proposed Option 1 two-step approach that EPA should consider in developing the final rule. For instance, we seek commenters' views on whether the Agency should adopt a first step of standards but defer any second step of standards to a planned future rulemaking on heavy-duty GHG emissions instead of adopting a second step of standards in this rulemaking. We also request comment on whether there are additional factors that we should consider when setting standards out to the MY 2031 timeframe.

As explained in Section III.B.3, we have evaluated and considered the costs of these technologies in our assessment of the proposed Options 1 and 2 standards. The proposed Options 1 and 2 standards are achievable without increasing the overall fuel consumption and CO₂ emissions of the engine for each of the duty cycles (FTP, SET, and LLC) and the fuel mapping test procedures defined in 40 CFR 1036.535 and 1036.540, as discussed in the Chapter 3 of the draft RIA. Finally, the proposed Options 1 and 2 standards would have no negative impact on safety, based on the existing use of these technologies in light-duty vehicles and heavy-duty engines on the road today.

B. Summary of Proposed Compression-Ignition Exhaust Emission Standards and Proposed Duty Cycle Test Procedures

1. Current Duty Cycle Test Procedures and Standards

Current criteria pollutant standards must be met by compression-ignition engines over both the Federal Test Procedure (FTP) and the Supplemental Emission Test (SET) duty cycles. The FTP duty cycles, which date back to the 1970s, are composites of a cold-start and a hot-start transient duty cycle designed to represent urban driving. There are separate duty cycles for both SI and CI engines. The cold-start emissions are weighted by one-seventh and the hot-start emissions are weighted by six-sevenths. The SET is a more recent duty cycle for diesel engines that is a continuous cycle with ramped transitions between the thirteen steady-state modes. The SET does not include engine starting and is intended to represent fully warmed-up operating modes not emphasized in the FTP, such as more sustained high speeds and loads.

Emission standards for criteria pollutants are currently set to the same numeric value for FTP and SET test cycles. Manufacturers of compression-ignition engines have the option to participate in our averaging, banking, and trading (ABT) program for NO_X and PM as discussed in Section IV.G. These pollutants are subject to family emission limit (FEL) caps of 0.50 g/hp-hr for NO_X and 0.02 g/hp-hr for PM.

EPA developed powertrain and hybrid powertrain test procedures for the HD GHG Phase 2 Heavy-Duty Greenhouse Gas rulemaking (81 FR 73478, October 25, 2016) with updates in the HD Technical Amendments rule (86 FR 34321, June 29, 2021). The powertrain and hybrid powertrain tests allow manufacturers to directly measure the effectiveness of the engine, the transmission, the axle and the integration of these components as an input to the Greenhouse gas Emission Model (GEM) for compliance with the greenhouse gas standards. As part of the technical amendments, EPA allowed the powertrain test procedure to be used beyond the current GEM drive cycles to include the FTP and SET engine-based test cycles and to facilitate hybrid powertrain testing (40 CFR 1036.505 and 1036.510 and 40 CFR 1037.550).

These heavy-duty diesel-cycle engine standards are applicable for a useful life period based on the primary intended service class of the engine. For certification, manufacturers must demonstrate that their engines will meet these standards throughout the useful life by performing a durability test and applying a deterioration factor (DF) to their certification value.

Additionally, manufacturers must adjust emission rates for engines with exhaust aftertreatment to account for infrequent regeneration events accordingly. To account for variability in these measurements, as well as production variability, manufacturers typically add margin between the DF and infrequent regeneration adjustment factor (IRAF) adjusted test result, and the family emission limit (FEL). A summary of the margins manufacturers have included for MY 2019 and newer engines is summarized in Chapter 3.1.2 of the draft RIA.

2. Proposed Test Procedures and Standards

EPA is proposing new NO_X, PM, HC, and CO emission standards for heavy-duty compression-ignition engines that will be certified under 40 CFR part 1036. We are proposing updates to emission standards for our existing laboratory test cycles ( i.e., FTP and SET) and proposing NO_X , PM, HC and CO emission standards based on a new low-load test cycle (LLC) as described below. The proposed standards for NO_X, PM, and HC are in units of milligrams/horsepower-hour instead of grams/horsepower-hour because using units of milligrams better reflects the precision of the new standards, rather than adding multiple zeros after the decimal place. Making this change would require updates to how manufacturers report data to the EPA in the certification application, but it does not require changes to the test procedures that define how to determine emission values. We describe compression-ignition engine technology packages that demonstrate the feasibility of achieving these proposed Options 1 and 2 standards in Section III.B.3.ii and provide additional details in Chapters 2 and 3 of the draft RIA for this rulemaking.

As part of this rulemaking, we are proposing two options to increase the useful life for each engine class as described in Section IV.A. The proposed Options 1 and 2 emission standards outlined in this section would apply for the longer useful life periods and manufacturers would be responsible for demonstrating that their engines will meet these standards as part of the proposed revisions to durability requirements described in Section IV.F. In Section IV.G, we discuss our proposed updates to the ABT program to account for our proposal of three laboratory cycles (FTP, SET and LLC) with unique standards.

As discussed in Section III.B.2, the proposal includes two sets of standards: Proposed Option 1 and proposed Option 2. As described in Section III.B.3.ii, we believe the technology packages evaluated for this proposal can achieve our proposed Options 1 and 2 duty-cycle standards. For Option 1, we are proposing the standards in two steps in MY 2027 and MY 2031, because the proposed Option 1 program includes not only numerical updates to existing standards but also other new and revised standards and compliance provisions such as a new duty-cycle procedure and standards, revised off-cycle procedures and standards, longer useful life periods, and other proposed requirements that, when considered collectively, merit a phased approach to lead time. As discussed in Section I.G and in Section III.B.4, we also present an alternative set of standards (Alternative) that we also considered. The Alternative is more stringent than either the proposed Option 1 MY 2031 standards or proposed Option 2 because the Alternative has shorter lead time, lower numeric NO_X emission standards and longer useful life periods. We note that we currently are unable to conclude that the Alternative is feasible in the MY 2027 timeframe over the useful life periods in this Alternative in light of deterioration in the emission control technologies that we have evaluated to date, and we expect that we would need additional supporting data or other information in order to determine that the Alternative is feasible in the MY 2027 timeframe to consider adopting it in the final rule.

The proposed options for NO_X standards were derived to consider the range of options that may potentially be appropriate to adopt to achieve the maximum feasible emissions reductions from heavy-duty diesel engines considering lead time, stability, cost, energy and safety. To accomplish this, we evaluated what operation made up the greatest part of the inventory as discussed in Section VI.B and what technologies could be used to reduce emissions in these areas. As discussed in Section I, we project that emissions from operation at low power, medium-to-high power, and mileages beyond the current regulatory useful life of the engine would account for the majority of heavy-duty highway emissions in 2045. To achieve reductions in these three areas we identified options for cycle-specific standards to ensure that the maximum achievable reductions are seen across the operating range of the engine. As described in Section IV, we are proposing to increase both the regulatory useful life and the emission-related warranty periods to ensure these proposed standards are met for a greater portion of the engine's operational life.

To achieve the goal of reducing emissions across the operating range of the engine, we are proposing two options for standards for three duty cycles (FTP, SET and LLC). In proposing these standards, we assessed the performance of the best available aftertreatment systems, which are more efficient at reducing NO_X emissions at the higher exhaust temperatures that occur at high engine power, than they are at reducing NO_X emissions at low exhaust temperatures that occur at low engine power. To achieve the maximum NO_X reductions from the engine at maximum power, the aftertreatment system was designed to ensure that the downstream selective catalytic reduction (SCR) catalyst was properly sized, diesel exhaust fluid (DEF) was fully mixed with the exhaust gas ahead of the SCR catalyst and the diesel oxidation catalyst (DOC) was designed to provide a molar ratio of NO to NO₂ of near one. To reduce emissions under low power operation and under cold-start conditions, we selected standards for proposed Option 1, for the LLC and the FTP that would achieve an 80 to 90 percent, or more, reduction in emissions under these operating conditions as compared to current standards. The proposed Options 1 and 2 standards are achievable by utilizing cylinder deactivation (CDA), dual-SCR aftertreatment configuration and heated diesel exhaust fluid (DEF) dosing. To reduce emissions under medium to high power, we selected standards for proposed Option 1, for the SET that would achieve a greater than 80 percent reduction in emissions under these operating conditions. The proposed Options 1 and 2 SET standards are achievable by utilizing improvements to the SCR formulation, SCR catalyst sizing, and improved mixing of DEF with the exhaust. Further information about these technologies can be found in Chapters 1 and 3 of the draft RIA.

For the proposed Options 1 and 2 PM standards, they were set at a level to maintain the current emissions performance of diesel engines. For the proposed Options 1 and 2 standards for HC and CO, they were generally set at a level that is achievable by spark-ignition engines. Each of these standards are discussed in more detail in the following sections.

In proposed Option 1 for MY 2031 and later Heavy HDE, we are proposing NO_X standards at an intermediate useful life (IUL) of 435,000 miles as discussed later in Section III.B.2. We believe that the proposed Option 1 useful life for these engines of 800,000 miles justifies the need for standards at IUL. It could be many years after the engines are on the road before EPA could verify that the engines meet the standards out to useful life if there is no IUL standard. As discussed further in Section III.B.3.ii.a, IUL standards ensure that the emissions from the engine are as low as feasible for the entire useful life and provides an intermediate check on emission performance deterioration over the UL.

As discussed in Section III.B.3, we have assessed the feasibility of the proposed Options 1 and 2 standards for compression-ignition engines by testing a Heavy HDE equipped with cylinder CDA technology and dual-SCR aftertreatment configuration with heated DEF dosing. The demonstration work consisted of two phases. The first phase of the demonstration was led by CARB and is referred to as CARB Stage 3. In this demonstration the aftertreatment was chemically- and hydrothermally-aged to the equivalent of 435,000 miles. During this aging the emissions performance of the engine was assessed after the aftertreatment was degreened, at the equivalent of 145,000 miles, 290,000 miles and 435,000 miles. The second phase of the demonstration was led by EPA and is referred to as the EPA Stage 3 engine. In this phase, improvements were made to the aftertreatment by replacing the zone-coated catalyzed soot filter with a separate DOC and diesel particulate filter (DPF) that were chemically- and hydrothermally-aged to the equivalent of 800,000 miles and improving the mixing of the DEF with exhaust prior to the downstream SCR catalyst. The EPA Stage 3 engine was tested at an age equivalent to 435,000 and 600,000 miles. The EPA Stage 3 engine will be tested at an age equivalent of 800,000 miles. Additionally, we plan to test a second aftertreatment system referred to as “Team A” which is also a dual-SCR aftertreatment configuration with heated DEF dosing, but has greater SCR catalyst volume and a different catalyst washcoat formulation.

i. FTP

We are proposing new emission standards for testing over the FTP duty-cycle as shown in Table III-2. These brake-specific FTP standards would apply across the primary intended service classes over the useful life periods shown in Table III-3. These Options 1 and 2 standards have been shown to be feasible for compression-ignition engines based on testing of the CARB Stage 3 and EPA Stage 3 engine with a chemically- and hydrothermally-aged aftertreatment system. At the time of this proposal, the catalyst was aged to an equivalent of 800,000 miles, but the test data at the equivalent of 800,000 miles was not yet available. EPA will continue to assess the feasibility of the proposed standards as additional demonstration data becomes available during the course of this rulemaking. For example, the EPA Stage 3 engine, and EPA's Team A demonstration engine will be aged to and tested at the equivalent of 800,000 miles. A summary of the data used for EPA's feasibility analysis can be found in Section III.B.3. To provide for additional margin, in our technology cost analysis we increased the SCR catalyst volume from what was used on the EPA and CARB Stage 3 engine. We are proposing to continue an averaging, banking, and trading (ABT) program for NO_X credits as a flexibility for manufacturers. Our proposal includes targeted revisions to the current ABT program, including new provisions to clarify how FELs apply for additional duty cycles, lower FEL caps for NO_X and restrictions for using NO_X emission credits (see Section IV.G for details on the ABT program).

The proposed Options 1 and 2, 5 mg/hp-hr (0.005 g/hp-hr) FTP standard for PM is intended to ensure that there is not an increase in PM emissions from future engines. As summarized in Section III.B.3.ii.b, manufacturers are submitting certification data to the agency for current production engines well below the proposed PM standard over the FTP duty cycle. Lowering the standard to 5 mg/hp-hr would ensure that future engines will maintain the low level of PM emissions of the current engines. Taking into account measurement variability of the PM measurement test procedure in the proposed PM standards, we believe that PM emissions from current diesel engines are at the lowest feasible level for MY 2027 and later engines. We request comment on whether 5 mg/hp-hr provides enough margin for particular engine designs. For example, would 6 or 7 mg/hp-hr be a more appropriate standard to maintain current PM emissions levels while providing enough margin to account for the measurement variability of the PM measurement test procedure.

We are proposing two options HC and CO standards based on the feasibility demonstration for SI engines. As summarized in Section III.B.3.ii.b, manufacturers are submitting data to the agency that show emissions performance for current production CI engines is well below the current and proposed standards. Keeping standards at the same value for all fuels is consistent with the agency's approach to previous criteria pollutant standards. See Section III.C for more information on how the numeric values of these two options for proposed HC and CO standards were determined.

In the ANPR, we requested comment on changing the weighting factors for the FTP cycle for heavy-duty engines. The current FTP weighting of cold-start and hot-start emissions was promulgated in 1980 (45 FR 4136, January 21, 1980). It reflects the overall ratio of cold and hot operation for heavy-duty engines generally and does not distinguish by engine size or intended use. Specifically, we asked if FTP weighting factors should vary by engine class and any challenges manufacturers may encounter to implement changes to the weighting factors. We did not receive any comments to change the weighting and received comments from Roush and MECA that the current weighting factors are appropriate. After considering these comments, we are not proposing any changes to the weighting factors.

ii. SET

We are proposing new emissions standards for the SET test procedure as shown in Table III-4 over the same useful life periods shown in Table III-3. Consistent with our current standards, we are proposing the same numeric values for the standards over the FTP and SET duty cycles, and the brake-specific SET standards apply across engine classes (primary intended service class). As with the FTP cycle, the Options 1 and 2 standards have been shown to be feasible for compression-ignition engines based on testing of the CARB Stage 3 and EPA Stage 3 engines with a chemically- and hydrothermally-aged aftertreatment system. At the time of this proposal, the catalyst was aged to an equivalent of 800,000 miles, but the test data at the equivalent of 800,000 miles was not yet available. EPA will continue to assess the feasibility of the proposed standards as additional data becomes available. To provide additional margin for meeting the SET standards, we have accounted for additional SCR catalyst volume in our cost analysis. A summary of the data used for EPA's feasibility analysis can be found in Section III.B.3.

As with the proposed PM standards for the FTP (see Section III.B.2.i), the proposed Options 1 and 2 P.M. standards for SET is intended to ensure that there is not an increase in PM emissions from future engines. We request comment on whether 5 mg/hp-hr provides enough margin for particular engine designs. For example, would 6 or 7 mg/hp-hr be a more appropriate standard to maintain current PM emissions levels while providing enough margin to account for the measurement variability of the PM measurement test procedure. As with the options for proposed HC and CO standards for the FTP (see Section III.B.2.i), we are proposing two options for standards for HC and CO based on the feasibility demonstration for SI engines (see Section III.C).

We have also observed an industry trend toward engine down-speeding—that is, designing engines to do more of their work at lower engine speeds where frictional losses are lower. To better reflect this trend in our duty cycle testing, in the HD GHG Phase 2 final rule, we promulgated new SET weighting factors for measuring CO₂ emissions (81 FR 73550, October 25, 2016). Since we believe these new weighting factors better reflect in-use operation of current and future heavy-duty engines, we are proposing to apply these new weighting factors to criteria pollutant measurement, as show in Table III-5, for NO_X and other criteria pollutants as well. To assess the impact of the new test cycle on criteria pollutant emissions, we analyzed data from the EPA Stage 3 engine that was tested on both versions of the SET. The data summarized in Section III.B.3.ii.a show that the NO_X emissions from the EPA Stage 3 engine at an equivalent of 435,000 miles are slightly lower using the proposed SET weighting factors in 40 CFR 1036.505 versus the current SET procedure in 40 CFR 86.1362. The lower emissions using the proposed SET cycle weighting factors are reflected in the stringency of the proposed Options 1 and 2 SET standards.

iii. LLC

EPA is proposing the addition of a low-load test cycle and standard that would require CI engine manufacturers to demonstrate that the emission control system maintains functionality during low-load operation where the catalyst temperatures have historically been found to be below their operational temperature (see Chapter 2.2.2 of the draft RIA). We believe the addition of a low-load cycle would complement the expanded operational coverage of our proposed off-cycle testing requirements (see Section III.C).

During “Stage 2” of their Low NO_X Demonstration program, SwRI and NREL developed several candidate cycles with average power and duration characteristics intended to test current diesel engine emission controls under three low-load operating conditions: Transition from high- to low-load, sustained low-load, and transition from low- to high-load. In September 2019, CARB selected the 92-minute “LLC Candidate #7” as the low load cycle they adopted for their Low NO_X Demonstration program and subsequent Omnibus regulation.

We are proposing to adopt CARB's Omnibus LLC as a new test cycle, the LLC. This cycle is described in Chapter 2 of the draft RIA for this rulemaking and test procedures are specified in the proposed 40 CFR 1036.512. The proposed LLC includes applying the accessory loads defined in the HD GHG Phase 2 rule. These accessory loads are 1.5, 2.5 and 3.5 kW for Light HDE, Medium HDE, and Heavy HDE engines, respectively. To allow vehicle level technologies to be recognized on this cycle we are proposing the powertrain test procedure to include the LLC. More information on the powertrain test procedure can be found in Section III.A.2.v. For the determination of IRAF for the LLC, we are proposing the test procedures defined in 40 CFR 1036.522, which is the same test procedure that is used for the FTP and SET. We believe that the IRAF test procedures that apply to the FTP and SET are appropriate for the LLC, but we request comment on whether to modify how the regeneration frequency value in 40 CFR 1065.680 is determined, to account for the fact that a regeneration frequency value is needed for three duty cycles and not just two.

Our proposed Options 1 and 2 emission standards for this proposed LLC are presented in Table III-6. The brake-specific LLC standards would apply across engine classes. As with the FTP cycle, the data from the EPA Stage 3 demonstration engine with an aged aftertreatment system shows that these proposed Options 1 and 2 standards are feasible with available margins between the data and the proposed standards. In fact, the margin between the proposed Option 1 MY 2031 standards and the Stage 3 engine data is the largest on the LLC, suggesting that a lower numeric NO_X standard would be feasible at 435,000 and 600,000 miles than included in the proposed Option 1 IUL NO_X standard. The summary of this data can be found in Section III.B.3.

We request comment on the addition of a low-load test cycle and standard, as well as the proposed accessory loads, or other engine operation a low-load cycle should encompass, if finalized.

The proposed LLC standards for PM are based on the effectiveness of the diesel particulate filter (DPF) to reduce PM emissions across the operating range of the engine, including under low loads. We request comment on whether 5 mg/hp-hr provides enough margin for particular engine designs. For example, would 6 or 7 mg/hp-hr be a more appropriate standard for the LLC to maintain current PM emissions levels while providing enough margin to account for the measurement variability of the PM measurement test procedure. Since we are not proposing standards on the LLC for SI engines, the data from the CARB and EPA Stage 3 engine discussed in Section III.B.3 were used to assess the feasibility of the proposed CO and HC standards. For both proposed Option 1 and Option 2 standards, we are proposing the same numeric standards for CO on the LLC as we have respectively proposed in Option 1 and Option 2 for the FTP and SET cycles. This is because the demonstration data of the EPA Stage 3 engine shows that CO emissions on the LLC are in similar to CO emissions from the FTP and SET. For the proposed Options 1 and 2 for HC standards on the LLC, we are proposing standards that are different than the standards of the FTP and SET cycles, to reflect the performance of the EPA Stage 3 engine on the LLC. The data discussed in Section III.B.3 of the preamble shows that the proposed Options 1 and 2 standards are feasible for both current and future new engines.

iv. Idle

CARB currently has an idle test procedure and accompanying standard of 30 g/h of NO_X for diesel engines to be “Clean Idle Certified”. In the Omnibus rule the CARB lowered the NO_X standard to 10 g/h for MY 2024 to MY 2026 engines and 5 g/h for MY 2027 and beyond. In the ANPR, we requested comment on the need or appropriateness of setting a federal idle standard for diesel engines. We received comments supporting action by EPA to adopt California's Clean Idle NO_X standard as a voluntary emission standard for federal certification. For proposed Option 1 we are proposing an optional idle standard in 40 CFR 1036.104(b) and a new test procedure in 40 CFR 1036.514, based on CARB's test procedure, to allow compression-ignition engine manufacturers to voluntarily choose to certify ( i.e., it would be optional for a manufacturer to include the idle standard in an EPA certification but once included the idle standard would become mandatory and full compliance would be required) to an idle NO_X standard of 30.0 g/hr for MY 2023, 10.0 g/hr for MY 2024 to MY 2026 and 5.0 g/hr for MY 2027 and beyond. As part of this optional idle standard, we are proposing to require that the brake-specific HC, CO, and PM emissions during the Clean Idle test may not exceed measured emission rates from the idle segments of the FTP or the idle mode in the SET, in addition to meeting the applicable idle NO_X standard. For proposed Option 2 we are proposing an idle NO_X standard of 10.0 g/hr for MY 2027 and beyond. We request comment on whether EPA should make the idle standards mandatory instead of voluntary for MY 2027 and beyond, as well as whether EPA should set clean idle standards for HC, CO, and PM emissions (in g/hr) rather than capping the idle emissions for those pollutants based on the measured emission levels during the idle segments of the FTP or the idle mode in the SET. We request comment on the need for EPA to define a label that would be put on the vehicles that are certified to the optional idle standard.

v. Powertrain

EPA recently finalized a separate rulemaking that included an option for manufacturers to certify a hybrid powertrain to the FTP and SET greenhouse gas engine standards by using a powertrain test procedure (86 FR 34321, June 29, 2021). In this rulemaking, we similarly propose to allow manufacturers to certify hybrid powertrains, BEVs, and FCEVs to criteria pollutant emissions standards by using the powertrain test procedure. In this section we describe how manufacturers could apply the powertrain test procedure to certify hybrid powertrains, and, separately, BEVs or FCEVs.

a. Development of Powertrain Test Procedures

Powertrain testing allows manufacturers to demonstrate emission benefits that cannot be captured by testing an engine alone on a dynamometer. For hybrid engines and powertrains, powertrain testing captures when the engine operates less or at lower power levels due to the use of the hybrid powertrain function; for BEVs and FCEVs powertrain testing allows the collection of data on work produced, energy used and other parameters that would normally be collected for an engine during a dynamometer test. However, powertrain testing requires the translation of an engine test procedure to a powertrain test procedure. Chapter 2 of the draft RIA describes how we translated the FTP, proposed SET for criteria pollutants, and proposed LLC engine test cycles to the proposed powertrain test cycles. The two primary goals of this process were to make sure that the powertrain version of each test cycle was equivalent to each respective engine test cycle in terms of positive power demand versus time and that the powertrain test cycle had appropriate levels of negative power demand. To achieve this goal, over 40 engine torque curves were used to create the powertrain test cycles. We request comment on ways to further improve the proposed powertrain test procedures, including approaches to apply the proposed procedures to powertrains that include a transmission as part of the certified configuration to make the idle accessory load more representative.

b. Testing Hybrid Engines and Hybrid Powertrains

As noted in the introduction of this Section III, we are proposing to clarify in 40 CFR 1036.101 that manufacturers may optionally test the hybrid engine and hybrid powertrain to demonstrate compliance. We propose that the powertrain test procedures specified in 40 CFR 1036.505 and 1036.510, which were previously developed for demonstrating compliance with GHG emission standards on the SET and FTP test cycles, are applicable for demonstrating compliance with criteria pollutant standards on the SET and FTP test cycles. In addition, for GHG emission standards we are proposing updates to 40 CFR 1036.505 and 1036.510 to further clarify how to carry out the test procedure for plug-in hybrids. We have done additional work for this rulemaking to translate the proposed LLC to a powertrain test procedure, and we are proposing that manufacturers could similarly certify hybrid engines and hybrid powertrains to criteria pollutant emission standards on the proposed LLC using the proposed test procedures defined in 40 CFR 1036.512.

We thus propose to allow manufacturers to use the powertrain test procedures to certify hybrid engine and powertrain configurations to all MY 2027 and later criteria pollutant engine standards. We also propose to allow manufacturers to begin using powertrain test procedures to certify hybrid configurations to criteria pollutant standards in MY 2023. Manufacturers could choose to use either the SET duty-cycle in 40 CFR 86.1362 or the proposed SET in 40 CFR 1036.505 in model years prior to 2027.

We are proposing to allow these procedures starting in MY 2023 for plug-in hybrids and, to maintain consistency with the requirements for LD plug-in hybrids, we are proposing that the applicable criteria pollutant standards must be met under the worst case condition, which is achieved by testing and evaluating emission under both charge depleting and charge sustaining operation. This is to ensure that under all drive cycles the powertrain meets the criteria pollutant standards and is not based on an assumed amount of zero emissions range. We are proposing changes to the test procedures defined in 40 CFR 1036.505 and 1036.510 to clarify how to weight together the charge depleting and charge sustaining greenhouse gas emissions for determining the greenhouse gas emissions of plug-in hybrids for the FTP and SET duty cycles. This weighting would be done using an application specific utility factor curve that is approved by EPA. We are also proposing to not apply the cold and hot weighting factors for the determination of the FTP composite emission result for greenhouse gas pollutants because the charge depleting and sustaining test procedures proposed in 40 CFR 1036.510 include both cold and hot start emissions by running repeat FTP cycles back-to-back. By running back-to-back FTPs, the proposed test procedure captures both cold and hot emissions and their relative contribution to daily greenhouse gas emissions per unit work, removing the need for weighting the cold and hot emissions. We request comment on our proposed approach to the FTP duty cycle for plug-in hybrids and the proposed approach to the determination of the FTP composite emissions result, including whether EPA should instead include cold and hot weighting factors for the latter. If you comment that EPA should include the cold and hot weighting factors, we request that you also include an example of how these calculations would be carried out with such an approach (how the calculations would include both the weighting of charge sustaining and charge depleting emissions in conjunction with the weighting of the cold and hot emissions results).

We propose to limit this test procedure to hybrid powertrains to avoid having two different testing pathways for non-hybrid engines for the same standards. On the other hand, there may be other technologies where the emissions performance is not reflected on the engine test procedures, so we request comment on whether this test procedure should be available to other powertrains, and if so how to define those powertrains.

Finally, for all pollutants, we request comment on if we should remove 40 CFR 1037.551 or limit the use of it to only selective enforcement audits (SEA). 40 CFR 1037.551 was added as part of the Heavy-Duty Phase 2 GHG rulemaking to provide flexibility for an SEA or a confirmatory test, by allowing just the engine of the powertrain to be tested. Allowing just the engine to be tested over the engine speed and torque cycle that was recorded during the powertrain test enables the testing to be conducted in more widely available engine dynamometer test cells, but this flexibility could increase the variability of the test results. If you submit comment in support of removing or limiting the use of 40 CFR 1037.551 to just SEA, we request that you include data supporting your comment.

c. Testing Battery-Electric and Fuel Cell Electric Vehicles

As noted in the introduction to this Section III, and detailed in Section IV.I, we are proposing to recognize the zero tailpipe emission benefits of BEV and FCEV technologies by allowing manufacturers to generate NO_X emission credits with these technologies. We are further proposing that manufacturers who choose to generate NO_X emission credits from BEVs or FCEVs would be required to conduct testing to measure work produced over a defined duty-cycle test, and either useable battery energy (UBE) for BEVs or fuel cell voltage (FCV) for FCEVs (see Section IV.I for details).

To conduct the testing necessary for generating NO_X emission credits from BEVs or FCEVs, we are proposing that manufacturers would use the powertrain test procedures for the FTP, proposed SET and proposed LLC. Specifically, for BEVs, manufacturers would run a series of powertrain FTP, SET and LLC tests over a defined sequence referred to as a “Multicycle Test” (MCT), which is specified in proposed 40 CFR 1037.552. For FCEVs, manufacturers would operate the powertrain over an FTP, SET, and LLC and determine the average fuel cell voltage (FCV) by taking the average of the FCV when the fuel cell current is between 55 percent and 65 percent of rated fuel cell current, as specified in proposed 40 CFR 1037.554.

The MCT for BEVs consists of a fixed number of dynamic drive cycles combined with constant-speed driving phases. The heavy-duty transient cycle (HDTC) described in current 40 CFR 1036.510(a)(4), LLC described in proposed 40 CFR 1036.512, and SET described in proposed 40 CFR 1036.505 are used to determine the energy consumption associated with specific and established driving patterns. These dynamic drive cycles make up a combined 57.92 miles of driving distance. The constant speed cycles (CSC), which are located in the middle and the end of the test, are intended to: Reduce test duration by depleting the battery more rapidly than the established certification drive schedules; improve the robustness of the energy determination by minimizing the impact of drive style variation; and prevent inconsistent triggering of end-of-test criteria that can occur at high power-demand points when a BEV is following a dynamic drive schedule at low states-of-charge.

The CSC middle phase is located after the initial run through two HDTCs, one LLC, and one SET. This CSC depletes the battery and allows determination of the vehicle's performance on the HDTC, LLC, and SET for both high and low states of charge. The distance traveled during the CSC middle phase that is determined by this procedure ensures that the second run through two HDTCs, one LLC, and one SET is conducted at a substantially lower state of charge. The target distance traveled over the CSC end phase is 20 percent or less of the total driven distance for the combined initial and second runs through the HDTC, LLC, or SET cycles.

The MCT for FCEVs consists of running a powertrain on the FTP, LLC, and SET to determine the FCV when the fuel cell current (FCC) is between 55 percent and 65 percent of rated FCC. Work is also measured during the second HDTC in the FTP and used in the determination of the FCEV conversion factor (CF) value for credit generation in proposed 40 CFR 1037.616.

We request comment on our proposed approach to powertrain testing for BEVs and FCEVs, and specifically whether any modifications of the FTP, SET and LLC powertrain test cycles would be needed for BEVs and FCEVs. We further request comment on whether the MCT, as defined in proposed 40 CFR 1037.552, would require modifications to accurately measure work produced over the FTP cycle or the measure of UBE. We request comment on whether the procedure in proposed 40 CFR 1037.554 is appropriate for determining FCV. Finally, we request comment on if current 40 CFR 1036.527 should be used to determine rated FCC.

vi. Closed Crankcase

During combustion, gases can leak past the piston rings sealing the cylinder and into the crankcase. These gases are called blowby gases and generally include unburned fuel and other combustion products. Blowby gases that escape from the crankcase are considered crankcase emissions (see 40 CFR 86.402-78). Current regulations restrict the discharge of crankcase emissions directly into the ambient air. Blowby gases from gasoline engine crankcases have been controlled for many years by sealing the crankcase and routing the gases into the intake air through a positive crankcase ventilation (PCV) valve. However, in the past there have been concerns about applying a similar technology for diesel engines. For example, high PM emissions venting into the intake system could foul turbocharger compressors. As a result of this concern, diesel-fueled and other compression-ignition engines equipped with turbochargers (or other equipment) were not required to have sealed crankcases (see 40 CFR 86.007-11(c)). For these engines, manufacturers are allowed to vent the crankcase emissions to ambient air as long as they are measured and added to the exhaust emissions during all emission testing to ensure compliance with the emission standards.

Because all new highway heavy-duty diesel engines on the market today are equipped with turbochargers, they are not required to have closed crankcases under the current regulations. Manufacturer compliance data indicate approximately one-third of current highway heavy-duty diesel engines have closed crankcases, indicating that some heavy-duty engine manufacturers have developed systems for controlling crankcase emissions that do not negatively impact the turbocharger. EPA is proposing provisions in 40 CFR 1036.115(a) to require a closed crankcase ventilation system for all highway compression-ignition engines to prevent crankcase emissions from being emitted directly to the atmosphere starting for MY 2027 engines. These emissions could be routed upstream of the aftertreatment system or back into the intake system. Unlike many other standards, this standard is a design standard rather than a performance standard.

Our reasons for proposing a requirement for closed crankcases are twofold. While the exception in the current regulations for certain compression-ignition engines requires manufacturers to quantify their engines' crankcase emissions during certification, they report non-methane hydrocarbons in lieu of total hydrocarbons. As a result, methane emissions from the crankcase are not quantified. Methane emissions from diesel-fueled engines are generally low; however, they are a concern for compression-ignition-certified natural gas-fueled heavy-duty engines because the blowby gases from these engines have a higher potential to include methane emissions. EPA proposed to require that all natural gas-fueled engines have closed crankcases in the Heavy-Duty Phase 2 GHG rulemaking, but opted to wait to finalize any updates to regulations in a future rulemaking, where we could then propose to apply these requirements to natural gas-fueled engines and to the diesel fueled engines that many of the natural gas-fueled engines are based off of (81 FR 73571, October 25, 2016).

In addition to our concern of unquantified methane emissions, we believe another benefit to closed crankcases would be better in-use durability. We know that the performance of piston seals reduces as the engine ages, which would allow more blowby gases and could increase crankcase emissions. While crankcase emissions are included in the durability tests that estimate an engine's deterioration, those tests were not designed to capture the deterioration of the crankcase. These unquantified age impacts continue throughout the operational life of the engine. Closing crankcases could be a means to ensure those emissions are addressed long-term to the same extent as other exhaust emissions.

Chapter 1.1.4 of the draft RIA describes EPA's recent test program to evaluate the emissions from open crankcase systems on two modern heavy-duty diesel engines. Results suggest THC and CO emitted from the crankcase can be a notable fraction of overall tailpipe emissions. By closing the crankcase, those emissions would be rerouted to the engine or aftertreatment system to ensure emission control.

3. Feasibility of the Diesel (Compression-Ignition) Engine Standards

i. Summary of Technologies Considered

Our proposed Options 1 and 2 standards for compression-ignition engines are based on the performance of technology packages described in Chapters 1 and 3 of the draft RIA for this rulemaking. Specifically, we are evaluating the performance of next-generation catalyst formulations in a dual SCR catalyst configuration with a smaller SCR catalyst as the first substrate in the aftertreatment system for improved low-temperature performance, and a larger SCR catalyst downstream of the diesel particulate filter to improve NO_X conversion efficiency during high power operation and to allow for passive regeneration of the particulate filter. Additionally, the technology package includes CDA that reduces the number of active cylinders, resulting in increased exhaust temperatures for improved catalyst performance under light-load conditions and can be used to reduce fuel consumption and CO₂ emissions. The technology package also includes the use of a heated DEF injector for the upfront SCR catalyst; the heated DEF injector allows DEF injection at temperatures as low as approximately 140 °C. The heated DEF injector also improves the mixing of DEF and exhaust gas within a shorter distance than with unheated DEF injectors, which enables the aftertreatment system to be packaged in a smaller space. Finally, the technology package includes hardware needed to close the crankcase of diesel engines.

ii. Summary of Feasibility Analysis

a. Projected Technology Package Effectiveness and Cost

Based upon preliminary data from EPA's diesel demonstration research and the CARB Heavy-duty Low NO_X Stage 3 Research Program (see Chapter 3.1.1.1 and Chapter 3.1.3.1 of the draft RIA), Heavy HDE NO_X reductions of 90 percent from current NO_X standards are technologically feasible when using CDA or other valvetrain-related air control strategies in combination with dual SCR systems. EPA has continued to evaluate aftertreatment system durability via accelerated aging of advanced emissions control systems as part of EPA's diesel engine demonstration program that is described in Chapter 3 of the draft RIA. In assessing the feasibility of our proposed standards, we have taken into consideration the proposed level of the standards, the additional emissions from infrequent regenerations, the proposed longer useful life, and lead time for manufacturers.

Manufacturers are required to design engines that meet the duty cycle and off-cycle standards throughout their useful life. In recognition that emissions performance will degrade over time, manufacturers design their engines to perform significantly better than the standards when first sold to ensure that the emissions are below the standard throughout useful life even as the emissions controls deteriorate. As discussed below and in Chapter 3 of the draft RIA, manufacturer margins can range from less than 25 percent to 100 percent of the FEL. For Option 1, for Heavy HDEs that have the longest proposed useful life, we are proposing intermediate useful life standards that ensure that engines do not degrade in performance down to the duty cycle and off-cycle standards too quickly and allow for an intermediate check on emissions performance deterioration over the useful life.

To assess the feasibility of the proposed Option 1 MY 2031 standards for heavy HDE at the IUL of 435,000 miles, the data from the EPA Stage 3 engine was used. As discussed in Section III.B.2 the EPA Stage 3 engine includes improvements beyond the CARB Stage 3 engine, namely replacing the zone-coated catalyzed soot filter with a separate DOC and DPF and improving the mixing of the DEF with exhaust for the downstream SCR. These improvements lowered the emissions on the FTP, SET and LLC below what was measured with the CARB Stage 3 engine. The emissions for the EPA Stage 3 engine on the FTP, SET and LLC aged to an equivalent of 435,000 and 600,000 miles are shown in Table III-7 and Table III-8. To assess the feasibility of the proposed Option 1 NO_X standards for MY 2027 and MY 2031 for Heavy HDE at the respective proposed Option 1 useful life periods, the data from the EPA Stage 3 engine was used. The data from the EPA Stage 3 engine was used because it included emission performance with the aftertreatment at the equivalent age of 435,000 and 600,000 miles. Having data at multiple points allowed us to use linear regression to project out the performance of the EPA Stage 3 engine at 800,000 miles. To account for the IRAF for both particulate matter and sulfur on the aftertreatment system, we relied on an analysis by SwRI that is summarized in Chapter 3 of the draft RIA. In this analysis SwRI determined the IRAF at 2 mg/hp-hr for both the FTP and SET cycles and 5 mg/hp-hr for the LLC. Based on our analysis, the proposed Option 1 MY 2027 and MY 2031 emissions standards for Heavy HDE are feasible at the respective proposed useful life periods. To provide for additional margin, in our technology cost analysis we increased the SCR catalyst volume from what was used on the EPA and CARB Stage 3 engine. The increase in total SCR catalyst volume relative to the EPA and CARB Stage 3 SCR was approximately 23.8 percent. We believe this further supports our conclusion that the proposed Option 1 standards are achievable for the proposed useful life of 800,000 miles for MY 2031 Heavy HDE. In addition to NO_X, the proposed Option 1 HC and CO standards are feasible for CI engines on all three cycles. This is shown in Table III-7, where the demonstrated HC and CO emissions results are below the proposed Option 1 standards discussed in Section III.B.2. The proposed Option 1 standards for PM of 5 mg/hp-hr for the FTP, SET and LLC, continue to be feasible with the additional technology and control strategies needed to meet the proposed Option 1 NO_X standards, as seen by the PM emissions results in Table III-7 below. As discussed in Section III.B.2, taking into account measurement variability of the PM measurement test procedure, we believe that PM emissions from current diesel engines are at the lowest feasible level for MY 2027 and later engines. We request comment on whether 5 mg/hp-hr provides enough margin for particular engine designs or for any of the duty cycles (FTP, SET, or LLC). For example, would 6 or 7 mg/hp-hr be a more appropriate standard for the LLC to maintain current PM emissions levels while providing enough margin to account for the measurement variability of the PM measurement test procedure. In addition, we request comment on if there are technologies that EPA could consider that would enable a PM standard lower than 5 mg/hp-hr. Commenters requesting a higher standard are encouraged to provide data supporting such comments.

As additional data is received from the EPA led demonstration project, the demonstration data will inform whether the proposed Option 1 IUL standards for MY 2031 are needed. For example, if the demonstration data shows much lower emissions for the first half of useful life than for the second half of useful life, then this would confirm our assumption that the proposed Option 1 IUL standard would ensure that the emission reductions during the earlier portion of an engine's useful life are achieved, while preserving sufficient margin for deterioration during the second half of useful life. On the other hand, if we find that the emissions values are relatively constant through useful life, this may support that an IUL standard may not be needed. This data will also inform whether the proposed Option 1 IUL standard of 20 mg/hp-hr at 435,000 miles is appropriate for Heavy HDE in MY 2031 and whether an IUL standard is also needed for MY 2027 to account for deterioration out to the proposed Option 1 600,000-mile useful life for MY 2027.

Our analysis also shows that the proposed Option 2 standards could be met starting in MY 2027 with CDA and dual-SCR with heated dosing (see draft RIA Chapter 3 for details of our analysis) as shown in Table III-7. The proposed Option 2 includes a higher (less stringent) NO_X emission level for all CI engine classes over the FTP and SET compared to either step of our proposed Option 1 NO_X FTP and SET standards. The FTP and SET standards in proposed Option 2 for PM, HC, and CO are numerically equivalent to our proposed Option 1 MY 2031 standards. As shown in Table III-7, we currently have data demonstrating that the proposed Option 2 standards could be met out to 600,000 miles. These data show the proposed Option 2 standards are feasible through the proposed Option 2 useful life periods for Light HDE, Medium HDEs. Our evaluation of the current data suggests that the proposed Option 2 standards would also be feasible out to the proposed Option 2 Heavy HDE useful life; we are continuing to collect data to confirm our extrapolation of data out to the longer useful life mileage. As discussed in Section IV.A, useful life mileages for proposed Option 2 are higher than our MY 2027 proposed useful life, but lower than our proposed Option 2 useful life values for MY 2031.

In addition to evaluating the feasibility of the new criteria pollutant standards, we also evaluated how CO₂ was impacted on the CARB Stage 3 engine. To do this we evaluated how CO₂ emissions changed from the base engine on the FTP, SET, and LLC, as well as the fuel mapping test procedures defined in 40 CFR 1036.535 and 1036.540. For all three cycles the Stage 3 engine emitted CO₂ with no measurable difference compared to the base 2017 Cummins X15 engine. Specifically, we compared the CARB Stage 3 engine including the 0-hour (degreened) aftertreatment with the 2017 Cummins X15 engine including degreened aftertreatment and found the percent reduction in CO₂ for the FTP, SET and LLC, was 1, 0 and 1 percent respectively. We note that after this data was taken SwRI made changes to the thermal management strategies of the CARB Stage 3 engine to improve NO_X reduction at low SCR temperatures. The data from the EPA Stage 3 engine at the equivalent age of 435,000 miles includes these calibration changes, and although there was an increase in CO₂, which resulted in the CO₂ emissions for the EPA Stage 3 engine being higher than the 2017 Cummins X15 engine for the FTP, SET and LLC of 0.6, 0.7 and 1.3 percent respectively, this was not a direct comparison because the 2017 Cummins X15 aftertreatment had not been aged to an equivalent of 435,000 miles. As discussed in Chapter 3 of the draft RIA, aging the EPA Stage 3 engine included exposing the aftertreatment to ash, that increased the back pressure on the engine, which contributed to the increase in CO₂ emissions from the EPA Stage 3. To evaluate how the technology on the CARB Stage 3 engine compares to the 2017 Cummins X15 with respect to the HD GHG Phase 2 vehicle CO₂ standards, both engines were tested on the fuel mapping test procedures defined in 40 CFR 1036.535 and 1036.540. These test procedures define how to collect the fuel consumption data from the engine for use in GEM. For these tests the CARB Stage 3 engine was tested with the development aged aftertreatment. The fuel maps from these tests were run in GEM and the results from this analysis showed that the Stage 3 engine emitted CO₂ at the same rate as the 2017 Cummins X15. The details of this analysis are described in Chapter 3.1 of the draft RIA. The technologies included in the EPA demonstration engine were selected to both demonstrate the lowest criteria pollutant emissions and have a negligible effect on GHG emissions. Manufactures may choose to use other technologies to meet the proposed standards, but manufacturers will still also need to comply with the GHG standards that apply under HD GHG Phase 2. Because of this we have not projected an increase in GHG emissions resulting from compliance with the proposed standards.

Table III-9 summarizes the incremental technology costs for the proposed Options 1 and 2 standards, from the baseline costs shown in Table III-13. While the standards vary between the proposed Option 1 and the proposed Option 2 standards, we are evaluating the same technologies to assess the feasibility of the two sets of standards. These values include aftertreatment system and CDA costs. The details of this analysis can be found in Chapter 3 of the draft RIA. Differences in the useful life and warranty periods between the proposed Options 1 and 2 are accounted for in the indirect costs as discussed in Chapter 7.1.2 of the draft RIA.

As described in Chapter 3.1 of the draft RIA, we have estimated the incremental technology cost for closed crankcase filtration systems for all CI engines to be $37 (2017 $), noting that these technologies are on some engines available in the market today.

b. Baseline Emissions and Cost

The basis for our baseline technology assessment is the data provided by manufacturers in the heavy-duty in-use testing program. This data encompasses in-use operation from nearly 300 LHD, MHD, and HHD vehicles. Chapter 5 of the draft RIA describes how the data was used to update the MOVES model emissions rates for HD diesel engines. Chapter 3 of the draft RIA summarizes the in-use emissions performance of these engines.

We also evaluated the certification data submitted to the agency. The data includes test results adjusted for IRAF and FEL that includes adjustments for deterioration and margin. The certification data, summarized in Table III-10, shows that manufacturers vary in their approach to how much margin is built into the FEL. Some manufactures have greater than 100 percent margin built into the FEL, while other manufacturers have less than 25 percent.

In addition to analyzing the on-cycle certification data submitted by manufacturers, we tested three modern HD diesel engines on an engine dynamometer and analyzed the data. These engines were a 2018 Cummins B6.7, 2018 Detroit DD15 and 2018 Navistar A26. These engines were tested on cycles that range in power demand from the creep mode of the Heavy Heavy-Duty Diesel Truck (HHDDT) schedule to the HD SET cycle defined in 40 CFR 1036.505. Table III-12 summarizes the range of results from these engines on the FTP, SET and LLC. As described in Chapter 3 of the draft RIA, the emissions of current production Heavy-Duty engines vary from engine to engine but the largest difference in NO_X between engines is seen on the LLC.

Table III-13 summarizes the baseline sales-weighted total aftertreatment cost of Light HDE, Medium HDE, Heavy HDE and urban bus engines. The details of this analysis can be found in Chapter 3 of the draft RIA.

4. Potential Alternative

We evaluated one alternative (the Alternative) to our proposed HD CI exhaust emission standards (summarized in Table III-14, Table III-15, and Table III-16). As discussed in this section and based on information we have collected to date, we do not project that the Alternative standards are feasible in the MY 2027 timeframe with the technology we have evaluated (Table III-9).

The Alternative we considered includes lower (more stringent) numeric NO_X emission levels for Heavy HDEs, and lower HC emission levels for all CI engine classes, combined with longer useful life periods and shorter lead time compared to the proposed Option 1 MY 2031 standards. As shown in Table III-7, the test data we currently have from the EPA Stage 3 engine is not sufficient to conclude that the Alternative standards would be feasible in the MY 2027 timeframe. Specifically, our data suggest that the numeric level of the FTP and SET NO_X emission standards would be very challenging to meet through 435,000 miles (see draft RIA Chapter 3.1). For Light HDEs and Medium HDEs, these data suggest that to meet the combination of numeric levels of the NO_X emission standards and useful life periods of the Alternative, it may be appropriate for EPA to consider providing manufacturers with additional lead time, beyond the MY 2027 implementation date of the Alternative. For Heavy HDEs, our extrapolation of the data from 600,000 miles through the 850,000 miles useful life period of the Alternative suggests that the numeric level of the NO_X emission control in the Alternative could not be maintained through the Alternative useful life period (see draft RIA Chapter 3.1 for details on available data and our evaluation). Wholly different emission control technologies than we have evaluated to date ( i.e., not based on CDA and a dual SCR) would be needed to meet the Alternative standards for Heavy HDEs; we request comment on this conclusion and on the availability, or potential development and timeline, of such additional technologies. We also note that the Alternative is significantly more stringent than the CARB Omnibus because of the combination of numeric level of the NO_X emission standards and useful life periods in the Alternative compared to the CARB Omnibus. Specifically, for heavy HDEs, the Alternative includes a 20 mg/hp-hr standard at a useful life of 850,000 miles, whereas for MYs 2027 through 2030 the CARB Omnibus includes a 20 mg/hp-hr standard at 435,000 miles and a 35 mg/hp-hr standard at 600,000 miles for heavy HDEs. Thus, the heavy HDE useful life period of the Alternative is substantially longer than the CARB Omnibus useful life periods that start in MY 2027, particularly when comparing the useful life period for the 20 mg/hp-hr standard. Starting in MY 2031, the CARB Omnibus NO_X standard for heavy HDEs is 40 mg/hp-hr at a useful life of 800,000 miles, which is again a higher numeric level of the standard at a shorter useful life than the Alternative.

For the optional idle NO_X standard, the Alternative includes a standard of 10.0 g/hr for MY 2027 and beyond. The proposed Options 1 and 2 standards generally represent the range of options, including the standards, regulatory useful life and emission-related warranty periods and lead time provided, that we are currently considering in this rule, depending in part on any additional information we receive on the feasibility, costs, and other impacts of the proposed Options 1 and 2 standards. In order to consider adopting the Alternative in the final rule, we would need additional data to project that the Alternative is feasible for the MY 2027 time frame. As discussed in Section III.B.5, we are soliciting comment on the feasibility of the Alternative and other alternatives outside the range of options covered by the proposed Options 1 and 2 standards.

5. Summary of Requests for Comment on the Stringency of the CI Duty Cycle Standards

We request comment on the following items related to the proposed CI duty cycle standards. First, we request comment on the numeric value of each proposed, or alternative, standard for each duty cycle and off-cycle emissions and the proposed Option 1 two step, or the proposed Option 2 one step, approach and implementation timetable, as well as other standards or approaches recommended by the commenter, within the approximate range of the proposed Options 1 and 2 standards. We request comment, including relevant data and other information, on the feasibility of the implementation model year, numeric levels of the emission standards, and useful life and warranty periods included in the Alternative, or other alternatives outside the range of options covered by the proposed Options 1 and 2 standards. We request comment on if a margin between the demonstrated emissions performance and the proposed standards should be included and if so, we request comment on if a specific margin should be used and what that value should be. Commenters requesting a specific margin are encouraged to provide data and analysis to support the numeric value of the margin(s).

We request comment on whether a lower numeric standard for NO_X should be set for the LLC based on the emission levels achieved with the CARB Stage 3 engine or EPA Stage 3 engine. We request comment on whether EPA should make the idle standards mandatory for MY 2027 and beyond. We request comment on whether the test procedures defined in 40 CFR 1036.522 for IRAF should be applied to the LLC or if alternative procedures should be considered. We request comment on whether the proposed PM standards of 5 mg/hp-hr for the FTP, SET and LLC provide enough margin to account for the measurement variability of the PM measurement test procedure, while ensuring that the PM emissions from HD CI engines do not increase. We are requesting comment on whether we should include HEV, BEV, and/or FCEV technologies in our feasibility analysis for the final rule.

As discussed in Section III.B.2.v, EPA requests comment on the proposed powertrain test procedure, including any additional requirements that are needed to ensure that the engine and respective powertrain cycles are equivalent. We request comment on other improvements that could be made specifically to make the idle accessory load more representative for powertrains that include a transmission as part of the certified configuration. EPA requests comment on whether the powertrain test procedure option is needed for specific non-hybrid powertrains where the engine test procedure is not representative of in-use operation of the powertrain in a vehicle, and if so how should we define these powertrains so that the powertrain test option is only available for these powertrains. We request comment on our proposed approach to powertrain testing for BEVs and FCEVs, and specifically whether any modifications of the FTP, SET and LLC powertrain test cycles would be needed for BEVs and FCEVs. We further request comment on whether the MCT as defined in 40 CFR 1037.552 would require modifications to accurately measure work produced over the FTP cycle or the measure of useable battery energy (UBE). We request comment on whether the procedure in 40 CFR 1037.554 is appropriate for determining fuel cell voltage (FCV). In addition, we request comment on if 40 CFR 1036.527 should be used to determine rated FCC.

Finally, we request comment on whether the standards should be expressed in units of milligrams per kilowatt-hour, so that each value of the standards is in the international system of units (SI units), as we have done for the HD nonroad and locomotive standards.

C. Summary of Compression-Ignition Off-Cycle Standards and In-Use Test Procedures

1. Current NTE Standards and Need for Changes to Off-Cycle Test Procedures

Heavy-duty CI engines are currently subject to Not-To-Exceed (NTE) standards that are not limited to specific test cycles, which means they can be evaluated not only in the laboratory but also in-use. NTE standards and test procedures are generally referred to as “off-cycle” standards and test procedures. These off-cycle emission limits are 1.5 (1.25 for CO) times the laboratory certification standard or family emission limit (FEL) for NO_X, HC, PM and CO and can be found in 40 CFR 86.007-11. NTE standards have been successful in broadening the types of operation for which manufacturers design their emission controls to remain effective, including steady cruise operation. However, there remains significant operation not covered by NTE standards.

Compliance with an NTE standard is based on emission test data (whether collected in a laboratory or in use) analyzed pursuant to 40 CFR 86.1370 to identify NTE events, which are intervals of at least 30 seconds when engine speeds and loads remain in the NTE control area or “NTE zone”. The NTE zone excludes engine operation that falls below certain torque, power, and speed values. The NTE procedure also excludes engine operation that occurs in certain ambient conditions ( i.e., high altitudes, high intake manifold humidity), or when aftertreatment temperatures are below 250°C. Collected data is considered a valid NTE event if it occurs within the NTE zone, lasts at least 30 seconds, and does not occur during any of the exclusion conditions (ambient conditions, or aftertreatment temperature).

The purpose of the NTE test procedure is to measure emissions during engine operation conditions that could reasonably be expected to occur during normal vehicle use; however, only data in a valid NTE event is then compared to the NTE emission standard. Our analysis of existing heavy-duty in-use vehicle test data indicates that less than ten percent of a typical time-based dataset are part of valid NTE events, and hence subject to the NTE standards; the remaining test data are excluded from consideration. We also found that emissions are high during many of the excluded periods of operation, such as when the aftertreatment temperature drops below the 250°C exclusion criterion. Our review of in-use data indicates that extended time at low load and idle operation results in low aftertreatment temperatures, which in turn lead to diesel engine SCR-based emission control systems not functioning over a significant fraction of real-world operation. Test data collected as part of EPA's manufacturer-run in-use testing program indicate that low-load operation could account for greater than 50 percent of the NO_X emissions from a vehicle over a given workday.

For example, 96 percent of tests in response to 2014, 2015, and 2016 EPA in-use testing orders passed with NO_X emissions for valid NTE events well below the 0.3 g/hp-hr NO_X NTE standard. When we used the same data to calculate NO_X emissions over all operation measured, not limited to valid NTE events, the NO_X emissions were more than double those within the valid NTE events (0.5 g/hp-hr). The results were even higher when we analyzed the data to consider only NO_X emissions that occur during low load events.

EPA and others have compared the performance of US-certified engines and those certified to European Union emission standards and concluded that the European engines' NO_X emissions are lower in low-load conditions, but comparable to US-certified engines subject to MY 2010 standards under city and highway operation. This suggests that manufacturers are responding to the European certification standards by designing their emission controls to perform well under low-load operations, as well as highway operations.

The European Union “Euro VI” emission standards for heavy-duty engines require manufacturers to check for “in-service conformity” by operating their engines over a mix of urban, rural, and motorway driving on prescribed routes using portable emission measurement system (PEMS) equipment to measure emissions. Compliance is determined using a work-based windows approach where emissions data are evaluated over segments or “windows.” A window consists of consecutive 1 Hz data points that are summed until the engine performs an amount of work equivalent to the European transient engine test cycle (World Harmonized Transient Cycle).

EPA is proposing an approach similar to the European in-use program, with key distinctions that build upon the Euro VI approach, as discussed below.

2. Proposed Off-Cycle Standards and Test Procedures

As described in Section III.C.1, our current NTE test procedures were not designed to capture low-load operation. We are proposing to replace the NTE test procedures and standards (for NO_X , PM, HC and CO) for model year 2027 and later engines. Engine operation and emissions test data would be assessed in 300-second moving average windows (MAWs) of continuous engine operation. In contrast to the current NTE approach that divides engine operation into two categories (in the NTE zone and out of the NTE zone), the proposed approach would divide engine operation into three categories (or “bins”) based on the time-weighted average engine power of each MAW of engine data as described in more detail below.

Although the proposed program has similarities to the European approach, we are not proposing to limit our standards to operation on prescribed routes. Our current NTE program is not limited to prescribed routes and we would consider it an unnecessary step backward to change that aspect of the procedure.

In Section IV.G, we discuss our proposed updates to the ABT program to account for our proposal of unique off-cycle standards.

i. Bins

We are proposing two options of off-cycle standards for three bins of operation that cover the range of operation included in the duty cycle test procedures and operation that is outside of the duty cycle test procedures for each regulated pollutant (NO_X, HC, CO, and PM). The three bins represent three different domains of emission performance. The idle bin represents extended idle operation and other very low load operation where engine exhaust temperatures may drop below the optimal temperature for aftertreatment function. The medium/high load bin represents higher power operation including much of the operation currently covered by the NTE. Operation in the medium/high load bin naturally involves higher exhaust temperatures and catalyst efficiencies. The low load bin represents intermediate operation and could include a large fraction of urban driving. Because the proposed approach divides 300 second windows into bins based on time-averaged engine power of the window, any of the bins could include some idle or high power operation. Like the duty cycle standards, we believe that more than a single standard is needed to apply to the entire range of operation that heavy-duty engines experience. A numerical standard that would be technologically feasible under worst case conditions such as idle would necessarily be much higher than the levels that are achievable when the aftertreatment is functioning optimally. Similarly, since the low load bin will consist of operation either between the idle and medium/high load bins or be an average of the operation in the two bins, the work specific emissions of the low load bin will generally be lower than the idle bin and higher than the medium/high load bin. Section III.C.2.iii includes the proposed Options 1and 2 off-cycle standards.

Given the challenges of measuring engine power directly in-use, we are proposing to use the CO₂ emission rate (grams per second) as a surrogate for engine power in defining the bins for an engine. We are further proposing to normalize CO₂ emission rates relative to the nominal maximum CO₂ rate of the engine. So, if an engine with a maximum CO₂ emission rate of 50 g/sec was found to be emitting CO₂ at a rate of 10 g/sec, its normalized CO₂ emission rate would be 20 percent. We are proposing that the maximum CO₂ rate be defined as the engine's rated maximum power multiplied by the engine's family certification level (FCL) for the FTP certification cycle. We request comment on whether the maximum CO₂ mass emission rate should instead be determined from the steady-state fuel mapping procedure in 40 CFR 1036.535 or the torque mapping procedure defined in 40 CFR 1065.510. We propose the bins to be defined as follows:

• Idle bin: 300 second windows with normalized average CO₂ rate ≤ 6 percent

• Low-load bin: 300 second windows with normalized average CO₂ rate > 6 percent and ≤ 20 percent

• Medium/high-load bin: 300 second windows with normalized average CO₂ rate > 20 percent

The proposed bin cut points of six and twenty percent are near the average power of the proposed low-load cycle and the FTP, respectively. We request comment on whether the cut points should be defined at different power levels or if other metrics should be used to define the bins. We also request comment on whether it would be more appropriate to divide in-use operation into two bins rather than three bins and, if so, what the cut point should be.

To ensure that there is adequate data in each of the bins to compare to the off-cycle standards, we are proposing a minimum of 2,400 moving average windows per bin. We are proposing that if during the first shift day each of the bins does not include at least 2,400 windows, then the engine would need to be tested for additional day(s) until the minimum requirement is met. We are also proposing that the engine can be idled at the end of the shift-day to meet the minimum window count requirement for the idle bin. This is to ensure that even for duty cycles that do not include significant idle operation the minimum window count requirement for the idle bin can be met without testing additional days. We request comment on whether 2,400 windows is the appropriate minimum to sufficiently reduce variability in the results while not requiring an unnecessary number of shift-days to be tested to meet the requirement.

ii. Off-Cycle Test Procedures

We are proposing to measure off-cycle emissions using the existing test procedures that specify measurement equipment and the process of measuring emissions during field testing in 40 CFR part 1065. We are proposing in part 1036 subpart F the process for recruiting test vehicles, how to test over the shift-day, how to evaluate the data, what constitutes a valid test, and how to determine if an engine family passes. Measurements may use either the general laboratory test procedures in 40 CFR 1065, or the field test procedures in 40 CFR part 1065, subpart J. However, we are proposing special calculations for low load and medium/high load bins in 40 CFR 1036.515 that would supersede the brake-specific emission calculations in 40 CFR part 1065. The proposed test procedures would require second-by-second measurement of the following parameters:

• Molar concentration of CO₂ (ppm)

• Molar concentration of NO_X (ppm)

• Molar concentration of HC (ppm)
• Molar concentration of CO (ppm)
• Concentration of PM (g/m3)
• Exhaust flow rate (m3/s)

Mass emissions of CO₂ and each regulated pollutant would be separately determined for each 300-second window and would be binned based on the normalized CO₂ rate for each window.

The standards described in Section III.C.2.iii are expressed in units of g/hr for the idle bin and g/hp-hr for the low and medium/high load bins. However, unlike most of our exhaust standards, the hp-hr values for the off-cycle standards do not refer to actual brake work. Rather, they refer to nominal equivalent work calculated proportional to the CO₂ emission rate. Thus, we are proposing in 40 CFR 1036.515 that the NO_X emissions (“e”) in g/hp-hr would be calculated as:

We are proposing a limited number of exclusions that would exclude some data from being subject to the off-cycle standards. The first exclusion is for data collected during periodic PEMS zero and span drift checks or calibrations, where the emission analyzers are not available to measure emissions during that time and these checks/calibrations are needed to ensure the robustness of the data. Data would also be excluded anytime the engine is off during the course of the shift-day, including engine off due to automated start/stop, as no exhaust emissions are being generated by the engine while it is not operating. We are also proposing to exclude data when ambient temperatures are below −7 °C, or when ambient temperatures are above the altitude-based value determined using Equation 40 CFR 1036.515-1. The colder temperatures can significantly inhibit the engine's ability to maintain aftertreatment temperature above the minimum operating temperature of the SCR catalyst while the higher temperature conditions at altitude can limit the mass airflow through the engine, which can adversely affect the engine's ability to reduce engine out NO_X through the use of exhaust gas recirculation (EGR). In addition to affecting EGR, the air-fuel ratio of the engine can decrease under high load, which can increase exhaust temperatures above the conditions where the SCR catalyst is most efficient at reducing NO_X . Data would also be excluded for operation at altitudes greater than 5,500 feet above sea level for the same reasons as for high temperatures at altitude. We would also exclude data when any approved Auxiliary Emission Control Device (AECD) for emergency vehicles are active because the engines are allowed to exceed the emission standards while these AECDs are active. Data collected during infrequent regeneration events would also be excluded due to the fact that the data collected may not include enough operation during the infrequent regeneration to properly weight the emissions rates during an infrequent regeneration event with emissions that occur without an infrequent regeneration event. We request comment on the appropriateness of these exclusions and whether other exclusions should be included. We request comment on whether emissions during infrequent regeneration should be included in determining compliance with the proposed off-cycle standards and if so, how these emissions should be included such that the emissions are properly weighted with the emissions when infrequent regenerations are not occuring. While data is excluded when any approved ACEDs for emergency vehicles are active, data generated while other approved ACEDs are active may not be excluded from the emissions calculations under the proposed 40 CFR 1036.515.

To reduce the influence of environmental conditions on the accuracy and precision of the PEMS, we are proposing additional requirements in 40 CFR 1065.910(b). These requirements are to minimize the influence of temperature, pressure, electromagnetic frequency, shock, and vibration on the emissions measurement. If the design of the PEMS or the installation of the PEMS does not minimize the influence of these environmental conditions the PEMS must be installed in an environmental chamber during the off-cycle test.

iii. Off-Cycle Standards

For NO_X and HC, we are proposing separate standards for distinct modes of operation. To ensure that the proposed duty-cycle NO_X standards and the proposed off-cycle NO_X standards are set at the same relative stringency level for each option, the idle bin standard is proportional to the voluntary Idle standard discussed in Section III.B.2.iv, the low load bin standard is proportional to the proposed LLC standard discussed in Section III.B.2.iii and the medium/high load bin standard is proportional to the proposed SET standard discussed in Section III.B.2.ii. For HC for each option the proposed low load bin standards are set at values proportional to the LLC standard and the medium/high load bin standard is proportional to the SET proposed standard. For PM and CO for each option the standards for the FTP, SET and LLC are the same numeric value, so the low load and medium/high load bin have the same standards. The proposed Options 1 and 2 off-cycle standards for the low load and medium/high load bin are shown in Table III-17. For the idle bin, the proposed Option 1 NO_X emission standard for all CI primary intended service classes is 10.0 g/hr starting in model years 2027 through 2030 and 7.5 g/hr starting in model year 2031. For proposed Option 2, the idle bin NO_X standard for all CI primary intended service classes is 15.0 g/hr starting in model year 2027. For PM, HC and CO we are not proposing standards for the idle bin because the emissions from these pollutants are very small under idle conditions and idle operation is extensively covered by the FTP, SET and LLC duty cycles discussed in Section III.B.2. We request comment on appropriate scaling factors or other approaches to setting off-cycle standards. Finally, we request comment on whether there is a continued need for measurement allowances in an in-use program such as described below. A discussion of the measurement allowance values can be found in Section III.C.5.iii.

3. Feasibility of the Diesel (Compression-Ignition) Off-Cycle Standards

i. Technologies

As a starting point for our determination of the appropriate numeric levels of our proposed off-cycle emission standards, we considered whether manufacturers could meet the duty-cycle standard corresponding to the type of engine operation included in a given bin, as follows:

• Idle bin operation is generally similar to operation at idle and the lower speed portions of the LLC.
• Low load bin operation is generally similar to operation over the LLC and the FTP.
• Medium/high load bin operation is generally similar to operation over the FTP and much of the SET.

An important question is whether the proposed off-cycle standards would require technology beyond what we are projecting would be necessary to meet the duty-cycle standards. As described below, we do not expect our proposed Options 1 and 2 off-cycle standards to require different technologies. However, the proposed Option 1 standard for the medium/high load bin would likely require manufacturers to increase the volume of the SCR catalyst.

This is not to say that we expect manufacturers to be able to meet these proposed Options 1 and 2 standards with no additional work. Rather, we project that the proposed Options 1 and 2 off-cycle standards could be met primarily through additional effort to calibrate the duty-cycle technologies to function properly over the broader range of in-use conditions. We also recognize that manufacturers could choose to include additional technology, if it provided a less expensive or otherwise preferred option.

When we evaluated the technologies discussed in Section III.B.3.i with emissions controls that were designed to cover a broad range of operation, it was clear that we should set the off-cycle standards to higher numerical values than the duty-cycle standards for the off-cycle test procedures being proposed. Section III.C.3.ii explains how the technology and controls performed when testing with the off-cycle test procedures over a broad range of operation. The data presented in Section III.C.3.ii shows that even though there are similarities in the operation between the duty cycles (LLC, FTP, and SET) and the off-cycle bins (Idle bin, Low load bin, and Medium/high load bin), the broader range of operation covered by the off-cycle test procedure results in a broader range in emissions performance, which justifies the need for higher off-cycle standards than the corresponding duty cycle standards. In addition to this, the off-cycle test procedures and standards cover a broader range of ambient temperature and pressure, which can also increase the emissions from the engine as discussed in Section III.C.2.ii. Commenters supporting lower or higher numerical standards are encouraged to consider the proposed level of the standards in the full context of the test procedures and compliance provisions. See Section III.C.6.

ii. Summary of Feasibility Analysis

To identify appropriate numerical levels for the off-cycle standards, we evaluated the performance of the EPA Stage 3 engine in the laboratory on five different cycles that were created from field data of HD engines that cover a range of off-cycle operation. These cycles are the CARB Southern Route Cycle, Grocery Delivery Truck Cycle, Drayage Truck Cycle, Euro-VI ISC Cycle (EU ISC) and the Advanced Collaborative Emissions Study (ACES) cycle. The CARB Southern Route Cycle is dominantly highway operation with elevation changes resulting in extended motoring sections followed by high power operation. The Grocery Delivery Truck Cycle represents goods delivery from regional warehouses to downtown and suburban supermarkets and extended engine-off events characteristic of unloading events at supermarkets. Drayage Truck Cycle includes near dock and local operation of drayage trucks, with extended idle and creep operation. Euro-VI ISC Cycle is modeled after Euro VI ISC route requirements with a mix of 30 percent urban, 25 percent rural and 45 percent highway operation. ACES Cycle is a 5-mode cycle developed as part of ACES program. Chapter 3 of the draft RIA includes figures that show the engine speed, engine torque and vehicle speed of the cycles.

The engine was initially calibrated to minimize NO_X emissions for the proposed duty cycles (FTP, SET, and LLC). It was then further calibrated to achieve more optimal performance over the off-cycle operation. Although the engine did not include the SCR catalyst volume that is included in our cost analysis and that would enable lower medium/high load bin NO_X emissions, the test results shown in Table III-18 provide a reasonable basis for evaluating the feasibility of controlling off-cycle emissions to a useful life of 435,000 miles. Using this data along with the data from the CARB Stage 3 that was measured at multiple points in the age of the aftertreatment to project out the emissions level to 800,000 miles, the proposed Options 1 and 2 off-cycle NO_X standards at each respective useful life value are shown to be feasible. The summary of the results is in Chapter 3 of the draft RIA.

a. Idle Bin Evaluation

The proposed idle bin would include the idle operation and some of the lower speed operation that occurs during the LLC and FTP. However, it would also include other types of low-load operation observed with in-use vehicles, such as operation involving longer idle times than occur in the LLC. To ensure that the idle bin standard would be feasible, we set the proposed Option 1 idle bin standard in MY 2027 and MY 2031 at the level projected to be achievable engine-out with exhaust temperatures below the light-off temperature. As can be seen see from the results in Table III-18, the EPA Stage 3 engine performed well below the proposed Options 1 and 2 NO_X standards. The summary of the results is located in Chapter 3 of the draft RIA.

b. Low and Medium/High Load Bin Evaluations

As can be seen see from the results in Table III-18, the emissions from the Stage 3 engine in the low load bin were below the proposed Options 1 and 2 standards for each of the off-cycles standards. The HC and CO emissions measured for each of these off-cycle duty cycles was well below the proposed Options 1 and 2 off-cycle standards for the low and medium/high load bins. The summary of the results is located in Chapter 3 of the draft RIA.

For the medium/high load bin, four of the five off-cycle duty cycles had emission results below the proposed Option 1 NO_X standard for MY 2031 of 30 mg/hp-hr shown in Table III-17. As mentioned, in Section III.B.2 the engine did not include the SCR catalyst volume that is included in our cost analysis, so we will continue to evaluate the emissions performance from the EPA Stage 3 engine and we will evaluate an aftertreatment that includes this additional SCR volume referred to as EPA Team A. In addition, we will conduct testing with these aftertreatments after they have been aged to the equivalent of 800,000 miles to further evaluate the feasibility of the proposed Option 1 off-cycle standards for the full proposed MY 2031 useful life period. For the proposed Option 2 medium/high load standards, our extrapolation of the data from 435,000 miles to the 650,000 useful life of proposed Option 2 indicates that the standards would be feasible starting in MY 2027.

We request comment on the proposed Options 1 and 2 off-cycle standards, as well as the overall structure of the off-cycle program. We also request comment on the need for fewer or more than 3 bins. As described in Section III.C.3.ii, the emissions from CARB Stage 3 engine have been demonstrated to be very similar across the three bins, which may indicate that some or all bins can be combined. On the other hand, this data was generated on the EPA Stage 3 engine with aftertreatment that was chemically- and hydrothermally-aged to the equivalent of 435,000 miles and as the aftertreatment is aged beyond 435,000 miles it may show a larger difference in NO_X emissions performance between the bins. See Chapter 3 of the draft RIA for more information on how the FTP, SET, and LLC NO_X emissions performance has changed from the degreened system to the aftertreatment aged to an equivalent of 600,000 miles.

4. Potential Alternatives

Following our approach for duty-cycle standards, we evaluated one set of alternative off-cycle exhaust emission standards (the Alternative) for CI HDE. These alternative off-cycle standards were derived using the same approach as the proposed off-cycle standards. ( i.e., by setting the alternative off-cycle standards as a multiple of the alternative certification duty-cycle standards). These off-cycle standards for the Alternative are set at 1.5 times the Clean Idle test standard (NO_X only) for the idle bin, 1.5 times the LLC standard for the low load bin, and 1.5 times the SET standard for the medium/high load bin. This approach resulted in the same standards in the Alternative and the proposed Options 1 and 2 standards for PM, but different standards for NO_X, HC and CO.

For the Alternative, data in Table III-18 show that the medium/high load bin off-cycle NO_X standard would be challenging to meet at a useful life of 435,000 miles. Our extrapolation of the data out to the 850,000 useful life for Heavy HDEs in this alternative suggests that this off-cycle standard is not feasible in the MY 2027 timeframe. We expect that wholly different emission control technologies than we have evaluated to date ( i.e., not based on CDA and a dual SCR) would be needed to meet the standards in the Alternative; we request comment on this conclusion and on the availability, or potential development and timeline, of such additional technologies.

As with the proposed standards, the data presented in Chapter 3 of the draft RIA shows that the Alternative PM, HC and CO standards are feasible for CI engines in MY 2027.

5. Compliance and Flexibilities for Off-Cycle Standards

Given the similarities of the proposed off-cycle standards and test procedures to the current NTE requirements that we are proposing they would replace starting in MY 2027, we have evaluated the appropriateness of applying the current NTE compliance provisions for the proposed Options 1 and 2 off-cycle standards, as discussed below. We are also requesting comment on a possible broadening of our in-use compliance strategy to cover more engines and more operation.

i. Relation of Off-Cycle Standards to Defeat Devices

CAA section 203 prohibits bypassing or rendering inoperative a certified engine's emission controls. When the engine is designed or modified to do this, the engine is said to have a defeat device. With today's engines, the greatest risks with respect to defeat devices involve manipulation of the electronic controls of the engine. EPA refers to an element of design that manipulates emission controls as an Auxiliary Emission Control Device (AECD). Unless explicitly permitted by EPA, AECDs that reduce the effectiveness of emission control systems under conditions which may reasonably be expected to be encountered in normal vehicle operation and use are prohibited as defeat devices under current 40 CFR 86.004-2.

For certification, EPA requires manufacturers to identify and describe all AECDs. For any AECD that reduces the effectiveness of the emission control system under conditions which may reasonably be expected to be encountered in normal vehicle operation and use, manufacturers must provide a detailed justification. We are proposing to migrate the definition of defeat device from 40 CFR 86.004-2 to 40 CFR 1036.115(h) and clarify that an AECD is not a defeat device if such conditions are substantially included in the applicable procedure for duty-cycle testing as described in 40 CFR 1036, subpart F. “Duty-cycle testing” in 40 CFR 1036.115(h)(1)(i) would not include the proposed off-cycle test procedure in 40 CFR 1036.515, since it is an off-cycle test procedure and not a duty-cycle test procedure for the purposes of this provision.

ii. Heavy-Duty In-Use Testing Program

Under the current manufacturer-run heavy-duty in-use testing (HDIUT) program, EPA annually selects engine families to evaluate whether engines are meeting current emissions standards. Once we submit a test order to the manufacturer to initiate testing, it must contact customers to recruit vehicles that use an engine from the selected engine family. The manufacturer generally selects five unique vehicles that have a good maintenance history, no malfunction indicators on, and are within the engine's regulatory useful life for the requested engine family. The tests require use of portable emissions measurement systems (PEMS) that meet the requirements of 40 CFR 1065, subpart J. Manufacturers collect data from the selected vehicles over the course of a day while they are used for their normal work and operated by a regular driver, and then submit the data to EPA. Compliance is evaluated with respect to the NTE standards.

We are proposing to continue the HDIUT program, with compliance with respect to the new off-cycle standards and test procedures that would be added to the program beginning with MY 2027 engines. We are also proposing to not carry forward the Phase 2 HDIUT requirements in 40 CFR 86.1915 beginning with MY 2027. Under the current NTE based off-cycle test program, if you are required to test ten engines under Phase 1 testing and less than 8 fully comply with the vehicle pass criteria in 40 CFR 86.1912, then we could require you to initiate Phase 2 HDIUT testing which would require you to test an additional 10 engines. We are proposing that compliance with the off-cycle standards would be determined by testing a maximum of 10 engines, which was the original limit under Phase 1 HDIUT testing in 40 CFR 86.1915. Similar to the current Phase 1 HDIUT requirements in 40 CFR 86.1912, the proposed 40 CFR 1036.425 requires initially testing five engines. If all five engines pass, you are done testing and your engine family is in compliance. If one of those engines does not comply fully with the off-cycle bin standards, you would then test a sixth engine. If five of the six engines tested pass, you are done testing and your engine family is in compliance. If two of the six engines tested do not comply fully with the off-cycle bin standards, you would then test four more for a total of 10 engines. The engine family would fail off-cycle standards if the arithmetic mean of the sum-over-sum emissions from the ten engines for any of the 3 bins for any of the pollutants is above the off-cycle bin standards. In regard to the averaging of data from the ten engines, we are proposing to take the arithmetic mean of the results by bin for each of the 10 engines determined in 40 CFR 1036.515(h) for each of the pollutants, thus creating mean bin results of each pollutant for each bin for the 10 engines. We request comment on determining this value by using all of the windows in a given bin for a given pollutant over all 10 of the engines tested.

We are also proposing to allow manufacturers to test a minimum of 2 engines using PEMS, in response to a test order program, provided they measure and report in-use data collected from the engine's on-board NO_X measurement system. This proposed option would be available only where a manufacturer receives approval based on the requirements in 40 CFR 1036.405(g).

We are proposing to not carry forward the provision in 40 CFR 86.1908(a)(6) that considers an engine misfueled if operated on a biodiesel fuel blend that is either not listed as allowed or otherwise indicated to be an unacceptable fuel in the vehicle's owner or operator manual. We are proposing in 40 CFR 1036.415(c)(1) to allow vehicles to be tested for compliance with the new off-cycle standards on any commercially available biodiesel fuel blend that meets the specifications for ASTM D975 or ASTM D7467. The proposal to make this change is based on the availability of biodiesel blends up to B20 throughout the United States and thus its use as a motor fuel in the heavy-duty fleet and the fact that engines must comply with the emission standards when operated on both neat ultra-low sulfur diesel (ULSD) and these biodiesel fuel blends.

Finally, we request comment on the need to measure PM emissions during in-use testing of new or existing engines subject to in-use testing if they are equipped with DPF. PEMS measurement is more complicated and time-consuming for PM measurements than for gaseous pollutants such as NO_X and eliminating it for some or all of in-use testing would provide significant cost savings. Commenters are encouraged to address whether there are less expensive alternatives for ensuring that engines meet the PM standards in use.

iii. PEMS Accuracy Margin

EPA worked with engine manufacturers on a joint test program to establish measurement allowance values to account for the measurement uncertainty associated with in-use testing in the 2008-time frame for gaseous emissions and the 2010-time frame for PM emissions to support NTE in-use testing. PEMS measurement allowance values in 40 CFR 86.1912 are 0.01 g/hp-hr for HC, 0.25 g/hp-hr for CO, 0.15 g/hp-hr for NO_X, and 0.006 g/hp-hr for PM. We are proposing to maintain the same values for HC, CO, and PM in this rulemaking. For NO_X we are proposing off-cycle NO_X accuracy margin (formerly known as measurement allowance) that is 10 percent of the off-cycle standard for a given bin. This accuracy margin was based on the Joint Research Council Real Driving Emissions (RDE): 2020 Assessment of Portable Emissions Measurement Systems (PEMS) Measurement Uncertainty. In this study, JRC arrived at an accuracy margin of 23 percent. They note that their Real Driving Emissions (RDE) program does not include linear drift correction of the emission measurements over the course of the shift-day. They have analytically determined that if they implement a linear zero drift correction over the course of the shift-day, the NO_X accuracy margin would be reduced to 10 percent. It should be noted that our off-cycle test procedures already include a linear zero and span drift correction over at least the shift day, and we are proposing to require at least hourly zero drift checks over the course of the shift day on purified air that, we believe, will result in measurement error that is on par with the analytically derived JRC value of 10 percent.

We are also in the process of further assessing the gaseous PEMS accuracy margin values for NO_X . There have been improvements made to the PEMS NO_X analyzers that were used in the emission original measurement allowance value determinations and some of these improvements were implemented in the testing that resulted in the 10 percent value derived by JRC and some were implemented after. Based on information from the on-going PEMS test program using the most current PEMS NO_X analyzers, we may make further revisions to the PEMS accuracy margin for NO_X for the off-cycle NO_X standards. This may result in finalizing a different accuracy margin or separate accuracy margins for each off-cycle bin NO_X standard that could be higher or lower than what we have proposed. As results become available from this study, we will add them to the docket.

These accuracy margins can be found in the proposed 40 CFR 1036.420. We request comment on our proposed approach to PEMS accuracy margins for assessing in-use compliance with NO_X and other pollutant standards.

As part of the PEMS measurement uncertainty analysis we will be continuing to evaluate proposed test procedure options that could further reduce the uncertainty of PEMS measurements. This evaluation includes the test procedures that define the drift check and drift correction, linearity requirements for the analyzers, and the requirements that define how the analyzer is zeroed and spanned throughout the test. We have proposed updates to 40 CFR 1065.935 to require hourly zeroing of the PEMS analyzers using purified air for all analyzers. We are also proposing to update the drift limits for NO_X analyzers to improve data quality. Specifically, for NO_X analyzers, we are proposing an hourly or more frequent zero verification limit of 2.5 ppm, a zero-drift limit over the entire shift day of 10 ppm, and a span drift limit between the beginning and end of the shift-day or more frequent span verification(s) of ±4 percent of the measured span value. We request comment on the proposed test procedure updates in 40 CFR 1065.935 and any changes that would reduce the PEMS measurement uncertainty.

iv. Demonstrating Off-Cycle Standards for Certification

Consistent with current certification requirements in 40 CFR 86.007-21(p)(1), we are proposing a new paragraph in 40 CFR 1036.205(p) that would require manufacturers to provide a statement in their application for certification that their engine complies with the off-cycle standards. Our proposal would require manufacturers to maintain record of any test data or engineering analysis they used as a basis for their statement but would not require manufactures to submit that information as part of their application. We request comment on our proposal to continue the practice of manufacturers submitting a statement without test data as a means of demonstrating compliance with off-cycle standards at certification.

For commenters suggesting manufacturers submit test data, we request comment on defining a specific test for manufacturers to demonstrate that they meet off-cycle standards at certification. The proposed off-cycle standards were designed to apply in-use when engines may not be operating on EPA's defined duty cycles. We are proposing that manufacturers use the off-cycle test procedure of 40 CFR 1036.515 when evaluating their in-use emission performance relative to the off-cycle standards. We request comment on demonstrating compliance with off-cycle standards by applying the off-cycle test procedure proposed in 40 CFR 1036.515 to one or more test cycles performed on an engine dynamometer. We solicit comment on alternatively demonstrating compliance with a field test using 40 CFR 1036.515.

6. Summary of Requests for Comment on the Stringency of the Off-Cycle Standards

The effective stringency of the proposed off-cycle standards is inherently tied to the way in which these standards are applied. To assist commenters in considering the stringency of the standards in the full context of the test procedures and compliance provisions, we have summarized these factors in Table III-20 below.

These factors can be considered individually, but commenters are encouraged to consider the tradeoffs between them. For example, commenters supporting a broader range of test conditions, could address the potential need for provisions to offset the stringency impact, such as higher standards.

We are proposing to sum the total mass of emissions for a given pollutant and divide by the sum of CO₂ mass emissions per bin once all the data has been separated into bins. This “sum-over-sum” approach would account for all emissions; however, it would require the measurement system (PEMS or a NO_X sensor) to provide accurate measurements across the complete range of emissions concentrations. We specifically request comments on the numeric values for the bin cut-points, the number of bins, the definition of the bin cut-point and the reference cycle for each bin. The importance of each of these values that define the proposed test procedure can be seen from the NO_X emissions achieved on the EPA Stage 3 engine which is summarized in Section III.B.3. This data shows that the emissions from this engine are relatively flat as a function of engine power. This data could suggest that either fewer bins are needed, for example combining the idle and low-load bin or that a different bin definition other than window average power should be used to bin the data.

We also request comment on the advantages and disadvantages of other statistical approaches that evaluate a percentile window(s) within each of the bins instead of the full data set as discussed in Chapter 3.2.3 in the draft RIA.

D. Summary of Spark-Ignition Heavy-Duty Engine Exhaust Emission Standards and Test Procedures

This section summarizes current exhaust emission standards and test procedures for certain spark-ignition (SI) heavy-duty engines and our proposed updates, as well as the feasibility demonstration and data that support our proposed changes.

Heavy-duty SI engines are largely produced by integrated vehicle manufacturers. These vehicle manufacturers sell most of their engines as part of complete vehicles but may also sell incomplete vehicles ( i.e., an engine and unassembled chassis components) to secondary vehicle manufacturers. In the latter case, secondary manufacturers, sometimes referred to as “finished vehicle builders,” complete the body and sell the final commercial vehicle product to the customer. Under current industry practice, the incomplete vehicle manufacturer ( i.e., chassis manufacturer) certifies both the engine and incomplete vehicle pursuant to all exhaust and evaporative emission requirements, performs testing to demonstrate compliance with the standards and provides the secondary manufacturer with build instructions to maintain compliance with the standards and to prevent the secondary manufacturer from performing modifications that would result in an un-certified configuration. Original chassis manufacturers and secondary manufacturers share responsibility for ensuring that the exhaust and evaporative emission control equipment is maintained in the final product delivered to the end customer.

1. Current Exhaust Emission Standards and Test Procedures

Current Otto-cycle (spark-ignition) heavy-duty engine exhaust emission standards in 40 CFR 86.008-10 apply to engines as provided in 40 CFR 86.016-1. The test procedure for these exhaust standards is the heavy-duty Federal Test Procedure (FTP), which includes an engine dynamometer schedule that represents urban driving. This test procedure is used for certification, SEA, and in-use emissions testing. Similar to the FTP duty cycle for CI engines, SI engine manufacturers evaluate their HD engines for exhaust emission standards by performing the FTP duty cycle under cold-start and hot-start conditions and determine a composite emission value by weighting the cold-start emission results and the hot-start emission results as specified in 40 CFR 86.008-10(a)(2)(v). This test cycle and cold/hot-start weighting was developed based on the typical operation of spark-ignition engines and differs from its compression-ignition counterpart in the normalized speed and torque setpoints, as well as the length of the cycle. The current SI engine exhaust emission standards for this duty cycle are identical to those for CI engines, as shown in Table III-21, consistent with the principle of fuel neutrality applied in recent light-duty vehicle criteria pollutant standards rulemakings.

To generate specific duty cycles for each engine configuration, engine manufacturers identify the maximum brake torque versus engine speed using the engine mapping procedures of 40 CFR 1065.510. The measured torque values are intended to represent the maximum torque the engine can achieve under fully warmed-up operation when using the fuel grade recommended by the manufacturer ( e.g., regular unleaded, 87 octane fuel) across the range of engine speeds expected in real-world conditions. The mapping procedure is intended to stabilize the engine at discrete engine speed points ranging from idle to the electronically-limited highest RPM before recording the peak engine torque values at any given speed. The provision in 40 CFR 1065.510(b)(5)(ii) allows manufacturers to perform a transient sweep from idle to maximum rated speed, which requires less time than stabilizing at each measurement point.

The HD Technical Amendments rulemaking migrated some heavy-duty highway engine test procedures from 40 CFR part 86 to part 1036. In addition to migrating the heavy-duty FTP drive schedule for SI engines from paragraph (f) of appendix I to part 86 to paragraph (b) of appendix II to part 1036, we added vehicle speed and road grade to the duty-cycle, which are needed to facilitate powertrain testing of SI engines for compliance with the HD Phase 2 GHG standards. As part of the drive schedule migration, negative normalized vehicle torque values over the HD FTP SI duty-cycle were removed.

2. Proposed Exhaust Emission Standards and Test Procedures

We are proposing to migrate the existing provisions for heavy-duty Otto-cycle engines from 40 CFR part 86, subpart A, into part 1036, with the migrated part 1036 provisions applying to heavy-duty SI engines starting in MY 2027. We are also proposing additional revisions as noted in this section.

Our proposed revisions to 40 CFR 1036.1 include migrating and updating the applicability provisions of 40 CFR 86.016-1. The provisions proposed in this section would apply for SI engines installed in vehicles above 14,000 lb GVWR and incomplete vehicles at or below 14,000 lb GVWR, but do not include engines voluntarily certified to or installed in vehicles subject to 40 CFR part 86, subpart S. We propose to update the primary intended service classes currently defined in 40 CFR 1036.140 to refer to new acronyms such that the proposed requirements in this section apply to the “Spark-ignition HDE” primary intended service class. Additionally, we are proposing updated Spark-ignition HDE exhaust emission standards in a new 40 CFR 1036.104. The proposal includes two sets of options for these standards: Proposed Option 1 and proposed Option 2. Proposed Option 1 would apply in two steps, with a first step in MY 2027 and a second step in MY 2031. Proposed Option 2 would apply in a single step starting in MY 2027. The two proposed options generally represent the range of lead time, standards, regulatory useful life periods, and emission-related warranty periods we are currently considering in this rule for HD SI engines.

As described in the following sections, Spark-ignition HDE certification would continue to be based on emission performance in lab-based engine dynamometer testing, with a proposed new SET duty cycle to address high load operation and idle emission control requirements to supplement our current FTP duty cycle. We are proposing two options to lengthen useful life and emissions warranty periods for all heavy-duty engines, including Spark-ignition HDE, as summarized in the following sections and detailed in Sections IV.A and IV.B.1 of this preamble. Engine manufacturers would continue to have the flexibility to participate in EPA's ABT program. We are proposing to update our ABT provisions in part 1036, subparts B and H, to reflect our proposed standards and useful life periods (see Section IV.G of this preamble). We are also proposing family emission limit (FEL) caps for NO_X in our proposed ABT program as described in the following sections.

i. Proposed Updates to the Federal Test Procedure and Standards

We propose to update 40 CFR part 1036, including the test procedure provisions of part 1036, subpart F, to apply for criteria pollutant testing. We propose that manufacturers would use the current FTP drive schedule of Appendix II of part 1036. As part of migrating the FTP drive schedule from part 86 to part 1036 in the recent HD Technical Amendment rulemaking, negative torque values were replaced with closed throttle motoring but there was no change to the weighting factors or drive schedule speed values. As shown in Table III-22, we are co-proposing two options to update our Spark-ignition HDE exhaust standards for the FTP duty cycle. The proposed Spark-ignition HDE exhaust standards maintain our fuel-neutral approach with standards that are numerically identical to the two steps of the proposed compression-ignition engine standards over our proposed lengthened Spark-ignition HDE useful life periods.

Our analysis of recent SI HDE certification data suggests that the proposed Options 1 and 2 standards are already nearly achievable for the existing useful life mileage values using emission control technologies available today. All SI heavy-duty engines currently on the market use a three-way catalyst (TWC) to simultaneously control NO_X , HC, and CO emissions. We project manufacturers would continue to use TWC technology and would adopt advanced catalyst washcoat technologies and refine their existing catalyst thermal protection (fuel enrichment) strategies to prevent damage to engine and catalyst components over our proposed longer useful life. Our feasibility analysis in Section III.D.3 describes the derivation of the proposed standards, including results from our SI technology demonstration program showing the feasibility of meeting these standards up to and beyond our proposed Options 1 and 2 useful life mileage values.

ii. Proposed Updates to Engine Mapping Test Procedure

As noted in Section III.D.1, manufacturers use the engine fuel mapping procedures of 40 CFR 1065.510 for certification. In Chapter 2.3.2 of our draft RIA, we describe torque variability that can result from the electronic controls used in SI engines. We are proposing updates to the engine mapping test procedure for heavy-duty engines to require that the torque curve established during the mapping procedure for highway heavy-duty engines be representative of the highest torque level possible when using the manufacturer's recommended fuel grade ( e.g., regular unleaded, 87 octane). Specifically, our proposed update to 40 CFR 1065.510(b)(5)(ii) would require manufacturers to disable any electronic controls that they report to EPA as an auxiliary emission control device (AECD) that would impact peak torque during the engine mapping procedure. We are proposing these updates to apply broadly for all engines covered under part 1065 (see 40 CFR 1065.1). Section XII.I of this preamble includes a discussion of proposed revisions to part 1065.

iii. Proposed Supplemental Emission Test and Standards

As discussed in Chapter 1 of the draft RIA, SI engines maintain stoichiometric air-fuel ratio control for a majority of the points represented on a fuel map. However, engine manufacturers program power enrichment and catalyst protection enrichment commands to trigger additional fuel to be delivered to the engine when either the engine requires a power boost to meet a load demand or high exhaust temperatures activate thermal protection for the catalyst. Generally, these strategies temporarily allow the engine to deviate from its “closed loop” control of the air-fuel ratio to increase the fraction of fuel ( i.e., fuel enrichment) and lower exhaust temperatures or increase engine power. Fuel enrichment is an effective means to protect the catalyst and increase engine power, but frequent enrichment events can lead to high criteria pollutant emissions and excessive fuel consumption not captured in existing test cycles. In Chapter 2.2 of the draft RIA, we highlight the opportunities to reduce emissions in high-load operating conditions where engines often experience enrichment for either catalyst protection or a power boost. Our feasibility discussion in Section III.D.3 presents thermal management, catalyst design, and engine control strategies engine manufacturers can implement to reduce enrichment frequency and associated emissions to meet our proposed standards.

Manufacturers implement enrichment strategies in real world operation when engines are above about 90 percent throttle for a duration that exceeds certain thresholds determined by the manufacturer. The FTP duty cycle currently used for engine certification does not capture prolonged operation in those regions of the engine map. Historically, in light of the limited range of applications and sales volumes of SI heavy-duty engines, especially compared to CI engines, we believed the FTP duty cycle was sufficient to represent the high-load and high-speed operation of SI engine-powered heavy-duty vehicles. As the market for SI engines increases for use in larger vehicle classes, these engines are more likely to operate under extended high-load conditions, causing us to more closely examine the adequacy of the test cycle in ensuring emissions control under real world operating conditions.

The existing supplemental emission test (SET) duty cycle, currently only applicable to CI engines, is a ramped modal cycle covering 13 steady-state torque and engine speed points that is intended to exercise the engine over sustained higher load and higher speed operation. We believe the SET procedure, including updates proposed in this rule, could be applied to SI engines and we are proposing to add the SET duty cycle and co-proposing two options for new SET emission standards for the Spark-ignition HDE primary intended service class. This new cycle would ensure that emission controls are properly functioning in the high load and speed conditions covered by that duty cycle. The proposed SET standards for Spark-ignition HDE are based on the same SET procedure, with the same proposed updates, as for heavy-duty CI engines, and we request comment on the need for any SI-specific provisions. Specifically, we request comment on the appropriateness of the CI-based weighting factors that determine the time spent ( i.e., dwell period) at each cycle mode. We encourage commenters to submit data to support any alternative dwell periods we should consider for SI engines.

We received comments in response to our ANPR discussion of the potential addition of an SET test cycle for HD SI engines. The commenter suggested that additional test cycles to capture sustained high load operation are not necessary and deviations from the FTP emission control strategies are addressed through the case-by-case AECD review process. While we agree that this process is available during the certification of an engine or vehicle, we believe it is more effective to evaluate the emission control system over measured test cycles with defined standards, where such test cycles are available, rather than relying solely on case-by-case identification by the manufacturer and review by EPA of the AECDs for each engine family. The commenter describes a high load enrichment AECD, which potentially increases CO, NMHC and PM emissions (see RIA Ch 3.2). However, the agency is also concerned about the potential for increased NO_X emissions during high load stoichiometric operation, where the enrichment AECD is not active. The current FTP transient cycle does not sufficiently represent these high load conditions, and we believe that the SET cycle is appropriate for evaluating this type of operation.

Similar to our fuel-neutral approach for FTP, we are proposing to align the SET standards for CI and SI engines, as shown in Table III-23. Specifically, we propose to adopt the SI HDE SET standards for NO_X and PM emissions based on the demonstrated ability of CI engines to control these emissions under high load conditions. The proposed Options 1 and 2 Spark-ignition HDE standards for HC and CO emissions on the SET cycle are numerically equivalent to the respective proposed FTP standards and are intended to ensure that SI engine manufacturers utilize emission control hardware and calibration strategies that maintain effective control of emissions during high load operation. We believe the proposed SET duty cycle and standards would accomplish this goal, and the level of our proposed Options 1 and 2 HC and CO standards are feasible over our proposed Options 1 and 2 useful life mileages based on our HD SI technology demonstration program summarized in Section III.D.3.ii.b. We request comment on the proposed SET test cycle and standards for Spark-ignition HDE, and any modifications we should consider to adapt the current CI-based SET duty cycle to SI HDEs.

We are also considering other approaches to address emissions from enrichment events during high load operation. Our current provisions in 40 CFR 86.004-28(j) require engine manufacturers to account for emission increases that are associated with aftertreatment systems that infrequently regenerate. Compression-ignition engine manufacturers currently apply these infrequent regeneration adjustment factor (IRAF) provisions to account for emission increases that may occur when the DPFs used for PM control on their engines require regenerations. These infrequent regeneration events use additional fuel to temporarily heat the DPF and clean the filter. Similar to the approach for infrequent regeneration events, the agency seeks comment on whether to require manufacturers to apply adjustment factors to SI FTP and/or SET emission test results to quantify the HC, CO, NO_X, and PM emission increases that occur due to enrichment AECDs. These factors would be quantified in a manner similar to that used in developing IRAFs, where they are based on the estimated real-world frequency and the measured emissions impact of these events.

iv. Proposed Idle Control for Spark-Ignition HDE

As described in Chapter 3.2 of the draft RIA, an idle test would assess whether the main component of the SI engine emission control system, the catalyst, remains effective during prolonged idle events. Heavy-duty SI engines can idle for long periods during loading or unloading of the vehicle cargo or to maintain cabin comfort ( i.e., heating or cooling) when the vehicle is parked.

Our primary concern for extended idle operation is that prolonged idling events may allow the catalyst to cool and reduce its efficiency resulting in emission increases including large emission increases on the driveaway until the catalyst temperatures increase. As discussed in the draft RIA, our recent HD SI test program showed idle events that extend beyond four minutes allow the catalyst to cool below the light-off temperature of 350 °C. The current heavy-duty FTP and proposed SET duty cycles do not include sufficiently long idle periods to represent these real-world conditions where the exhaust system cools below the catalyst's light-off temperature. We are proposing in a new paragraph at 40 CFR 1036.115(j)(1) to require the catalyst bed used in SI HDEs to maintain a minimum temperature of 350 °C to ensure emission control during prolonged idle; manufacturers would also be able to request approval of alternative strategies to prevent increased emissions during idling. We believe this minimum temperature requirement would sufficiently ensure emission control is maintained during idle, while addressing ANPR commenter concerns that our proposed idle requirements should not require significant additional test and certification costs. We request comment on this proposal, as well as additional or alternative strategies, such an idle test cycle and standard, that are capable of representing real-world operation and would address idle emissions not observed or measured on the current and proposed duty cycles. Commenters are encouraged to include data that represents engines expected to be available in the MY 2027 and later timeframe.

We recognize that over the next decade there may be an added incentive to generally reduce idling as a compliance strategy to meet EPA's heavy-duty greenhouse gas standards. Widespread adoption of idle reduction technologies, such as engine stop-start, may reduce the frequency and duration of prolonged idle and reduce the need for exhaust temperature thresholds. However, these idle reduction strategies may also cause emission increases when the engine is restarted, where the catalyst and oxygen sensors may have cooled and require a warm-up period. We request comment, including relevant data, on the expected adoption rate of idle reduction technologies ( e.g., stop-start) in the heavy-duty sector and the impact on criteria pollutant emissions when these technologies are in use.

v. Proposed Powertrain Testing Option for Hybrids

As summarized in Section III.B, we are proposing to expand the existing powertrain test procedures in 40 CFR 1037.550 to allow hybrid manufacturers to certify their products as meeting EPA's criteria pollutant standards. The procedure updates are intended to apply to both CI and SI-based hybrid systems, but many of the default vehicle parameters are based on CI systems. We request comment on the need for SI-specific vehicle parameters such as vehicle mass, drag coefficients, and rolling resistance coefficients.

vi. Proposed Thermal Protection Temperature Modeling Validation

Manufacturers utilize some form of catalyst or critical exhaust component temperature modeling within the ECM to determine when to activate fuel enrichment strategies to protect engine and catalyst hardware from excessive temperatures that may compromise durability. Manufacturers typically design these models during the engine development process by monitoring the actual temperatures of exhaust system components that have been instrumented with thermocouples during dynamometer testing. In these controlled testing conditions, manufacturers can monitor temperatures and stop the test to protect components from damage from any malfunctions and resulting excessive temperatures. The accuracy of these models used by manufacturers is critical in both ensuring the durability of the emission control equipment and preventing excessive emissions that could result from unnecessary or premature activation of thermal protection strategies.

The existing regulations require any catalyst protection strategies adopted by HD SI engine manufacturers to be reported to EPA in the application for certification as an AECD. The engine controls used to implement these strategies often rely on a modeling algorithm to predict high exhaust temperatures and to disable the catalyst, which can change the emission control strategy and directly impact real world emissions. During the certification process, manufacturers typically disclose the temperature thresholds of the critical components that need thermal protection and the parameter values ( e.g., time and temperature) at which the model activates the protection strategy. The agency has historically determined the appropriateness of these temperature limits based on information from engine manufacturers and component suppliers. We are proposing to standardize the process during certification of how a manufacturer discloses and validates a thermal protection model's performance.

In order to ensure that a manufacturer's model accurately estimates the temperatures at which thermal protection modes are engaged, the agency is proposing a validation process in a new paragraph 40 CFR 1036.115(j)(2) that would document the model performance during certification testing. The proposed validation process would require manufacturers to record component temperatures during engine mapping and the FTP and proposed SET duty cycles and a second-by-second comparison of the modeled temperature and the actual component temperature applications and submit as part of their certification. We propose that manufacturers must show that the measured component temperatures and the software-derived temperature model estimates are within 5 °C. This limitation on temperature differential is proposed to prevent model-based AECDs from being overly conservative in their design such that catalyst protection and resulting emissions increases due to fuel enrichment is triggered at lower temperatures than necessary. Manufacturers would be exempt from this model validation requirement for all engines that continuously monitor component temperatures via temperature sensors in lieu of thermal protection modeling.

As described in Section IV.C, we are proposing to expand the list of OBD parameters accessible using a generic scan tool. We are proposing that SI engine manufacturers monitoring component temperatures to engage thermal protection modes would make the component temperature parameters (measured and modeled, if applicable) publicly available, as specified in a new 40 CFR 1036.110(c)(4).

The agency seeks comment on this model validation proposal, including data that shows the frequency of preventable enrichment occurrences. We request comment on our proposed temperature allowance of 5 °C and whether we should require a specific type of thermocouple to measure the component temperatures. We also request comment on whether we should specify a method to filter temperature data to account for transient engine speed conditions. The agency also seeks comment on requiring manufacturers to incorporate temperature sensors on all production engines to continuously measure the temperature of any exhaust component that is currently protected by use of an enrichment strategy instead of relying on software models to estimate temperature. Currently, temperature sensors are used in production compression-ignition emission control systems and some light-duty SI applications.

vii. Proposed OBD Flexibilities

We recognize that there can be some significant overlap in the technologies and control systems adopted for products in the chassis-certified and engine-certified markets. These vehicles may share common engine designs and components, and their emission control systems may differ only in catalyst sizing and packaging and the calibration strategies used to meet the chassis- or engine-based emission standards.

We are proposing to further incentivize HD SI engine manufacturers to adopt their chassis-certified technologies and approaches in their engine-certified products so that the emission control strategies of their two product lines are more closely aligned. Specifically, we are proposing to limit the need for duplicate OBD certification testing if a manufacturer's chassis- and engine-certified technology packages are sufficiently similar. The current regulations in 40 CFR part 86 distinctly separate the OBD requirements based on GVWR. Under 40 CFR 86.007-17, engines used in vehicles at or below 14,000 lb GVWR are subject to the chassis-based OBD provisions of 40 CFR 86.1806. Engines in vehicles above 14,000 lb GVWR are subject to the engine-based provisions of 40 CFR 86.010-18 and there is no pathway for these larger vehicles to certify using the chassis-based OBD provisions.

In addition to the general heavy-duty OBD provisions proposed in new section 40 CFR 1036.110, we are proposing to allow vehicle manufacturers the option to request approval to certify the OBD of their spark-ignition, engine-certified products using data from similar chassis-certified Class 2b and Class 3 vehicles that meet the provisions of 40 CFR 86.1806-17. As part of the approval request, manufacturers would show that the engine- and chassis-certified products use the same engines and generally share similar emission controls ( i.e., are “sister vehicles”). Under this proposal, manufacturers would still be required to submit a separate application for certification for their engine-certified products, but EPA may approve the use of OBD testing data from sister vehicles at or below 14,000 lb GVWR class for the engine-certified products. We request comment on any additional provisions or limitations we should consider adopting related to aftertreatment characteristics, chassis configurations, or vehicle classes when evaluating a manufacturer's request to share OBD data between engine- and chassis-certified product lines. Specifically, we request comment, including data, on the impact of varying vehicle components such as transmissions, axle ratios, and fuel tank sizes on the OBD system. Finally, we request comment on additional compliance provisions, beyond OBD, that could be streamlined for these sister vehicles.

viii. Potential Off-Cycle Standards for Spark-Ignition HDE

As described in Section III.C, CI engines have been subject to not-to-exceed (NTE) standards and in-use testing requirements for many years. In Section III.C.2, we propose new off-cycle standards and updated in-use test procedures for CI engines. The proposed in-use test procedures in 40 CFR part 1036, subpart E, include the steps to perform the manufacturer-run field testing program for CI engines as migrated and updated from 40 CFR part 86, subpart T. The in-use procedures are based on a new moving average window (MAW) procedure in 40 CFR 1036.515 that separates in-use operation into idle, low load and medium/high load bins.

For SI engines, we request comment on setting off-cycle standards that would be based on an approach similar to the one taken by CARB in their HD Omnibus rulemaking. The Omnibus rule includes “in-use thresholds” ( i.e., off-cycle standards) for HD Otto cycle engines based on the laboratory-run FTP and SET duty cycles, and manufacturers may comply by attesting to meeting the in-use thresholds in their application for CARB certification. The CARB in-use thresholds apply to emissions measured over a shift day and processed into a single bin of operation. The thresholds from the single HD Otto cycle engine bin match CARB's standards in the medium/high load in-use bin for CI engines.

We are not proposing to include Spark-ignition HDE in our manufacturer-run field testing program at this time, and we currently lack in-use data to assess the feasibility of doing so, but we may consider it in a future rulemaking. We request comment on adopting in-use provisions similar to those for HD Otto cycle engines in CARB's program. Specifically, we request comment on allowing SI HDE manufacturers to attest to compliance with off-cycle standards in the application for certification and on not including SI HDE in our manufacturer-run field testing program. We request comment, including data, on the appropriate level of off-cycle standards we should consider for Spark-ignition HDE. Table III-24 presents a potential set of single bin off-cycle standards for Spark-ignition HDE that match the medium/high load in-use bin standards of proposed Options 1 and 2 for CI engines and similarly apply conformity factors to the proposed FTP and SET duty cycle standards for each pollutant ( i.e., 2.0 for MY 2027 through 2030 and 1.5 for MY 2031 and later under Option 1, and 1.5 for MY 2027 and later under Option 2). We request comment on these or other off-cycle standards we should consider for Spark-ignition HDE, including whether we should include additional in-use bins if we finalize LLC or other duty cycles in the future.

While we are not proposing off-cycle standards or a manufacturer-run in-use testing program for Spark-ignition HDE, we are soliciting comment on draft regulatory text that could be included in 40 CFR 1036.104 and 1036.515 and in 40 part CFR 1036, subpart E, with potential in-use provisions for Spark-ignition HDE. Even without a regulatory requirement for manufacturers to perform field testing, these test procedures would be valuable for Spark-ignition HDE manufacturers or EPA to compare in-use emissions to the duty cycle standards. Manufacturers could also use the procedures to verify their DF under the proposed PEMS testing option in 40 CFR 1036.246. We request comment on adopting in-use test procedures and setting off-cycle standards for Spark-ignition HDE, including data to support the appropriate level of the standards.

ix. Potential Low Load Cycle and Standards

Heavy-duty gasoline engines are currently subject to FTP testing, and we are proposing a SET procedure to evaluate emissions performance of HD SI engines under the sustained high speeds and loads that can produce high emissions. We are also considering whether a low-load cycle could address the potential for high emissions from SI engines when catalysts may not maintain sufficient internal temperature to remain effective.

Section III.B of this preamble describes the LLC duty cycle and standards we are proposing for HD compression-ignition engines. In our ANPR, we requested comment on the need for a low-load or idle cycle in general, and suitability of CARB's diesel-targeted low-load and clean idle cycles for evaluating the emissions performance of heavy-duty gasoline engines. One commenter suggested the higher exhaust temperatures of SI engines made catalyst deactivation less of a concern so that a low load cycle was not warranted.

As described in Section III.D.2.iv, we believe the proposed catalyst temperature control would effectively address idle emissions, but we recognize the value of demonstrating catalyst effectiveness during periods of prolonged idle and at low load, including when the vehicle accelerates from a stopped idle condition to higher speeds. We are soliciting comment on adopting a LLC duty cycle and standards for HD SI engines in addition to or in place of the idle control proposed in Section III.D.2.iv. We currently do not have test results demonstrating HD SI engine performance over the LLC duty cycle.

In considering Spark-ignition HDE standards over the LLC duty cycle, we solicit comment on applying LLC standards over the useful life periods of proposed Options 1 and 2 for the other Spark-ignition HDE standards. We also solicit comment on adopting the same numeric level of the standards for the same pollutants under proposed Options 1 and 2 for CI engines over the proposed Spark-ignition HDE useful life periods. We request comment on the benefits and challenges of an LLC standard for HD SI compliance, and encourage commenters to include emission performance data over the LLC duty cycle or other cycles that they believe would cause manufacturers to improve the emissions performance of their heavy-duty SI engines under lower load operating conditions.

3. Feasibility Analysis for the Proposed Exhaust Emission Standards

This section describes the effectiveness and projected costs of the control technologies that we analyzed in developing our proposed Spark-ignition HDE exhaust emission standards. In evaluating technology feasibility, we considered impacts on energy by monitoring CO₂ emissions, the lead time manufacturers need to develop and apply control strategies and implement performance demonstrations, and the need to maintain utility and safety of the engines and vehicles.

Our feasibility analyses for the proposed Options 1 and 2 FTP and SET exhaust emission standards are based on the HD SI technology demonstration program summarized in this section and detailed in Chapter 3.2.2.3 of the draft RIA. Feasibility of the proposed FTP standards is further supported by compliance data submitted by manufacturers for the 2019 model year. We also support the feasibility of the proposed Options 1 and 2 SET standards using engine fuel mapping data from a test program performed by the agency as part of the HD GHG Phase 2 rulemaking. See Chapter 3.2 of the draft RIA for more details related to these datasets.

i. Summary of Exhaust Emission Technologies Considered

This section summarizes the specific technologies and emission control strategies we considered as the basis for our proposed exhaust emission standards. The technologies presented in this section are described in greater detail in Chapters 1 and 3 of the draft RIA.

Our proposed Options 1 and 2 Spark-ignition HDE exhaust emission standards are based on the performance of the technology packages widely adopted for SI engines in chassis-certified vehicles today. We project manufacturers would meet our proposed standards by building on their existing TWC-based emission control strategies. Our technology demonstration evaluated advanced catalyst formulations, catalyst design changes including light-off catalysts located closer to the engine, engine down-speeding, and engine calibration strategies that can minimize enrichment during high-load and accelerate light-off for lower load and idle operations.

The catalyst system and related exhaust components have progressed in recent light-duty applications and are currently able to tolerate significantly higher exhaust gas temperatures while still maintaining emission control over the current useful life. We expect that improved materials, such as the advanced catalyst formulations evaluated in our technology demonstration, along with more robust temperature management would result in significant emission reductions and engines that are able to meet the proposed standards. The advanced catalyst formulations we evaluated were aged to 250,000 miles, which is longer than the useful life mileages that would apply under proposed Options 1 and 2 for Spark-ignition HDE.

Engine down speeding can help avoid the high speed, high exhaust gas temperature conditions that typically result in fuel enrichment due to engine component durability and catalyst thermal concerns. With the integration of modern multi-speed electronically controlled transmissions, this down speeding approach is extremely feasible and likely to also reduce engine wear and improve fuel consumption with little perceptible effect on performance for commercial vehicle operation. In our demonstration program, we reduced the base engine's manufacturer-stated maximum test speed of 4715 RPM to 4000 RPM to evaluate the impact of engine down-speeding.

ii. Projected Exhaust Emission Technology Package Effectiveness

a. Technology Effectiveness Over the FTP Duty Cycle

Our HD SI technology demonstration program evaluated several pathways manufacturers could use to achieve the proposed Options 1 and 2 standards. As shown in Table III-25, use of advanced catalysts provided substantial NO_X emission reductions over the FTP duty cycle beyond the performance demonstrated by technologies on recently certified engines. Engine down-speeding further decreased CO emissions while maintaining NO_X, NMHC, and PM control. Engine down-speeding also resulted in a small improvement in brake specific fuel consumption over the FTP duty cycle reducing from 0.46 to 0.45 lb/hp-hr. See Chapter 3.2.3 of the draft RIA for an expanded description of the test program and results.

We expect manufacturers could achieve similar emission performance by adopting other approaches, including a combination of calibration changes, optimized catalyst location, and fuel control strategies that EPA was unable to evaluate in our demonstration program due to limited access to proprietary engine controls.

In addition to our demonstration program, we evaluated the feasibility of the proposed Options 1 and 2 FTP standards by considering the performance of recently-certified engines. As detailed in Chapter 3.2.3.1 of the draft RIA, MY 2019 compliance data over the FTP duty cycle included the performance of six HD SI engine families from four manufacturers, representing the emission performance of all gasoline-fueled HD SI engines certified in MY 2019 as incomplete vehicles ( i.e., engine certified).

Table III-26 presents the manufacturer-reported MY 2019 levels for the three pollutants addressed by TWCs: NO_X , NMHC and CO. PM emissions for most of these SI engines were undetectable and reported as zero for certification. In the table, we identify the six certified engines by descending NO_X level and note that three of the six engines, representing over 70 percent of the MY 2019 engine-certified, gasoline-fueled HD SI engines, achieve a NO_X level that is less than half the current standard of 0.20 g/hp-hr ( i.e., 200 mg/hp-hr). When calibrating their engines, SI manufacturers experience tradeoffs in TWC performance for the three pollutants and each manufacturer may optimize their emission controls differently while complying with applicable emission standards. As expected, the certification results show no clear relationship between NMHC or CO emissions and the level of reduced NO_X among the various engine calibrations.

To evaluate the NMHC and CO emissions, we calculated an overall average for each pollutant that includes all engines, and separately averaged a smaller subset of the three engines ( i.e., Cert Engines 4-6) with the lowest NO_X levels. Table III-27 compares these two averages with the EPA 2010 standards and results from the engine family with the best NO_X emission performance of the MY 2019 compliance data.

Comparing the results in Table III-26 to the averages in Table III-27, we see that the overall average NMHC level of 59 mg/hp-hr and CO level of 5.9 g/hp-hr for the six engines are met by three engine families today. We expect at least one additional family could achieve the overall average NMHC and CO levels with calibration changes to adjust cold start catalyst light-off timing and refine the catalyst protection fuel enrichment levels. The NMHC and CO emissions averages for these MY 2019 engines align with our MY 2027 proposed Options 1 and 2 standards for those pollutants. The emission levels of the engine with the best NO_X performance are approaching the levels we are proposing for our Option 1 MY 2031 standards. While these recent certification results suggest it may be feasible for some manufacturers to meet the proposed Option 1 standards with current engine technology, it is less clear if the same emission levels could be maintained at the proposed useful life periods. We believe the combination of our proposed Option 1 standards and lengthened useful life would force some level of improved component durability or increased catalyst volumes beyond what is available on current HD SI engines and it will take additional time for manufacturers to develop their approach to complying.

b. Technology Effectiveness Over the SET Duty Cycle

As noted in Section III.D.2.iii, we are proposing Spark-ignition HDE standards for the SET duty cycle to ensure emissions are controlled under high load and speed conditions. Our HD SI technology demonstration program evaluated emission performance over the SET duty cycle. As shown in Table III-28, the NO_X and NMHC emissions over the SET duty cycle were substantially lower than the emissions from the FTP duty cycle (see Table III-25). Engine down-speeding improved CO emissions significantly, while NO_X, NMHC, and PM remained low. Engine down-speeding also resulted in a small improvement in brake specific fuel consumption over the SET duty cycle reducing from 0.46 to 0.44 lb/hp-hr. See Chapter 3.2.3 of the draft RIA for an expanded description of the test program and results.

Similar to our discussion related to the FTP standards, we expect manufacturers could achieve similar emission performance over the SET duty cycle by adopting other approaches, including a combination of calibration changes, optimized catalyst location, and fuel control strategies that EPA was unable to evaluate due to limited access to proprietary engine controls.

To evaluate the impact of fuel enrichment and supplement our SET feasibility analysis, we created a surrogate array of SET test points using HD SI engine fuel mapping data from a HD GHG Phase 2 test program (see Chapter 3.2.3 of the draft RIA). The test program tested a V10 gasoline engine on an early version of EPA's steady-state fuel mapping procedure that requires the engine to be run for 90 seconds at each of nearly 100 speed and torque points. The first 60 seconds at each point allowed the engine and fuel consumption to stabilize and the last 30 seconds were averaged to create the fuel map point.

For this analysis, we evaluated three subsets of the emissions data (NO_X, NMHC, and CO) over the range of engine speeds and torque values. The first subset of data included conditions where the engine went into power enrichment, as indicated by the air-fuel ratio. The second subset of data included conditions where the engine controller activated a catalyst protection fuel enrichment strategy before a power enrichment strategy was enabled. The third subset included only conditions where the engine maintained stoichiometric air-fuel ratio.

Peak torque points for each of these data subsets were used to calculate the A, B and C speeds and create three unique sets of surrogate SET test points. Emission rates for NO_X, NMHC, and CO shown in Table III-29 were calculated by interpolating the data subsets at each of the SET test points. Finally, the results were weighted according to the existing CI-based weighting factors outlined in 40 CFR 86.1362.

As observed in the surrogate SET test data, any enrichment mode, whether for power or catalyst protection purposes, resulted in substantial NMHC and CO emission increases from stoichiometric operation. When the engine was commanded into power enrichment mode and no longer maintained stoichiometric operation, NMHC and CO emissions rose 10 and 50 times higher, respectively. These results suggest that it is feasible for manufacturers to achieve low emission levels over the 13 modes of an SET duty cycle if their engines maintain stoichiometric operation. This can be accomplished with engine calibrations to optimize the TWC tradeoffs and fuel-air control strategies to limit preventable fuel enrichment.

iii. Derivation of the Proposed Standards

We are maintaining fuel neutrality of the proposed standards by applying the same numerical standards across all primary intended service classes. The proposed Options 1 and 2 NO_X and PM levels for the FTP and SET duty cycles are based on the emission performance of technologies evaluated in our HD CI engine technology demonstration program. We are basing the proposed Options 1 and 2 FTP and SET standards for HC and CO on HD SI engine performance as described in Section III.D.3.ii and summarized in this section.

Results from our HD SI technology demonstration program (see Table III-25 and Table III-28) show that the proposed NO_X standards based on our CI engine feasibility analysis are also feasible for HD SI engines over the FTP and SET duty cycles for both options. The proposed Option 1 MY 2031 NO_X standard was achieved by implementing an advanced catalyst with minor catalyst system design changes, and NO_X levels were further improved with engine down-speeding. The emission control strategies that we evaluated did not specifically target PM emissions, but we note that PM emissions remained low in our demonstration. We project HD SI engine manufacturers would be able to maintain near-zero PM levels with limited effort. We request comment on challenges manufacturers may experience to maintain effective PM control, including duty cycles other than FTP.

For proposed Option 1, starting in model year 2027, we are proposing to lower the HC and CO FTP standards consistent with the overall average NMHC and CO levels achieved by engine-certified, gasoline-fueled HD SI engines over the FTP cycle today (see Table III-27). We note that the MY 2019 engine certified with the lowest NO_X ( i.e., Cert Engine #6) is below our proposed MY 2027 NO_X standard (35 mg/hp-hr) and maintains NMHC and CO emissions below those average levels on the FTP cycle. We are proposing the same standards of 60 mg HC/hp-hr and 6.0 g CO/hp-hr would apply over the new SET duty cycle starting in MY 2027. We believe emission levels based on average engine performance today would be a low cost step to update and improve emission performance across all certified Spark-ignition HDE, and serve as anti-backsliding standards as manufacturers optimize their TWCs, implement a new duty cycle, and improve component durability in response to the proposed longer useful life periods. CO levels in our SET demonstration were above the proposed standard, but manufacturers have opportunities to reduce CO below our proposed standard by optimizing their TWC calibrations and maintaining stoichiometric conditions over more of their high load operation (see Table III-29).

Proposed Option 2 (MY 2027 and later) and step 2 of proposed Option 1 (MY 2031 and later) include the same proposed numeric HC standards of 40 mg HC/hp-hr and 6.0 g CO/hp-hr for the FTP and SET duty cycles. For the FTP duty cycle, results of our demonstration program show that the proposed HC standard would be achievable without compromising NO_X or CO emission control (see Table III-25). For the SET duty cycle, lower levels of NMHC were demonstrated, but at the expense of increased CO emissions in those higher load operating conditions (see Table III-28). The considerably lower NO_X and HC in our SET duty cycle demonstration results leave enough room for manufacturers to calibrate the tradeoff in TWC emission control of NO_X, HC, and CO to reduce CO below our proposed CO standard. For these reasons, we are proposing the FTP standard of 40 mg HC/hp-hr standard apply over the SET duty cycle. Proposed Options 1 and 2 generally represent the range of lead time, standards, and useful life periods we are currently considering in this rule for HD SI engines.

We request comment on the proposed Spark-ignition HDE FTP and SET standards, including the appropriateness of applying the same numeric emission levels for both duty cycles. Commenters suggesting more stringent standards are encouraged to provide data showing lower standards are achievable at their suggested useful life periods. We also request comment on our approaches to maintain fuel neutrality by proposing numerically identical standards for heavy-duty CI and SI engines.

iv. Summary of Costs To Meet the Proposed Exhaust Emission Standards

To project costs for HD SI technology packages manufacturers could adopt to meet the proposed standards, we combined manufacturers' HD SI MY 2019 compliance data into sales-weighted averages by vehicle category to account for aftertreatment system differences by engine. The discussion below summarizes our estimate of the technology costs to meet our proposed Spark-ignition HDE standards. See Chapter 3.2.3 of the draft RIA for an expanded description of the projected sales-weighted average catalyst volumes, PGM loadings, and other factors used to calculate our costs for HD SI engines and Section V of this preamble for a summary of how these technology costs are included in the overall cost of this proposal.

We calculated aftertreatment system costs for four categories of SI engines. The largest category, liquid-fueled SI engines, includes engines fueled by gasoline, ethanol, and ethanol blends, and represents the majority of HD SI engines on the market today. The second category, gaseous-fueled SI engines, includes engines fueled by compressed natural gas (CNG) or liquified petroleum gas (LPG). In addition to the general gaseous-fueled SI engines, we separately analyzed two subsets of gaseous-fueled SI engines (HHD and urban bus) that have unique market shares and distinct aftertreatment demands.

Table III-30 summarizes the projected technology costs for HD SI engines to meet our proposed standards. Chapter 3.2.3 of the draft RIA contains a more detailed breakdown of the costs. Our projected costs for the liquid-fueled SI engines are based on the aftertreatment system used in our HD SI technology demonstration program (see Section III.D.3). As shown in our demonstration program, liquid-fueled SI engine manufacturers could use the same catalyst systems in both proposed Options, including both steps (MY 2027 and 2031) of Option 1 to meet the proposed exhaust emission standards, so we projected a single cost. We request comment, including data, regarding calibration costs for manufacturers to optimize their Option 1 MY 2027 systems to meet the proposed Option 1 MY 2031 standards and costs for manufacturers to reprogram the existing electronics and software to down-speed their multi-speed transmissions. For this analysis, we assumed these costs would be part of the general research and development costs for the rule and did not separately quantify them. We did not make any additional cost adjustments to account for the proposed lengthened useful life, since the aftertreatment system used in the demonstration program represented catalysts aged to 250,000 miles.

We projected that most of the gaseous-fueled SI engines would include similar aftertreatment system upgrades as the liquid-fueled SI engines to meet the proposed standards and those costs are also summarized in Table III-30 and detailed in the draft RIA. The HHD and urban bus gaseous-fueled SI engine categories in our analysis had lower projected technology costs to meet the proposed standards. These two subsets include engines that were certified in MY 2019 to California's optional and more stringent 0.02 g/hp-hr NO_X standard. We assumed no additional technology would be needed for these engines to meet the proposed standards in future model years. Our projected costs for these engines were limited to durability improvements to the catalyst substrate support structure (can material, mat, seals, etc.) to meet the requirements of our proposed lengthened useful life mileages.

4. Potential Alternative

We also considered the emissions impact of an alternative (the Alternative) that is more stringent than our proposed Option 1 MY 2031 standards when considering the combination of numeric level of the standards, length of useful life, and lead time (see Table III-31 through Table III-33). The Alternative matches our proposed Option 1 MY 2031 FTP and SET standards for NO_X, PM, and CO, but has lower (more stringent) HC standards, and starts four years earlier for all pollutant standards, in MY 2027. The useful life and warranty mileages for the Alternative are also longer than those of proposed Option 1 for MYs 2031 and later SI engines. As shown in Table III-25 and Table III-28, available data indicate that the combination of NO_X, HC, and CO emission levels over the longer useful life period reflected in the Alternative standards would be very challenging to meet in the MY 2027 timeframe.

We believe the additional lead time provided by the second step of the proposed Option 1 MY 2031 standards, combined with the higher numeric standard for HC and the shorter useful life mileage, results in the proposed Option 1 standards being both feasible and technology forcing. Proposed Option 1 represents the most stringent range of lead time, standards, regulatory useful life periods, and emission-related warranty periods we are currently considering in this rule for HD SI engines unless we receive additional data to support a conclusion that the Alternative standards are feasible in the MY 2027 timeframe.

See Section 5.2.2. for more details on how we used MOVES to model our proposed options and alternative scenarios for the inventory analysis. We projected the same HD SI technology costs would apply for proposed Options 1 and 2. We believe the range of the proposed Options 1 and 2 standards could be achieved with the same advanced catalyst system from our demonstration program with complete access to calibration controls. That same catalyst system was aged to cover the range of useful life mileages included in the proposed options. See Section V of this preamble and Chapter 7 of the draft RIA for a description of the overall costs of the proposed options. Since we do not currently have information to indicate that the Alternative standards are feasible in the MY 2027 timeframe with the emission control technologies we evaluated, we are not presenting an analysis of the costs of the Alternative.

5. Summary of Requests for Comment

For heavy-duty SI engines, we are requesting comment regarding the cost, feasibility, and appropriateness of our proposed Options 1 and 2 standards, duty cycles, and test procedure updates. See the previous sections for specific requests for comment on each of those topics. When submitting comments, we request that commenters provide data, where possible, or additional references to support their positions.

We request comment on the implementation years of the program, the numeric levels of our proposed standards for FTP and SET duty cycles, and our approach to propose the same numeric standards for the two duty cycles and for both CI and SI engines.

We request comment on the proposed changes to test procedures, including the addition of the SET duty cycle and the disabling of AECDs that impact peak torque during engine mapping. We request commenters to include data to support recommended modifications to the CI-based SET duty cycle or powertrain test procedures for SI engine testing. We also seek comment on whether adjustment factors, similar to IRAFs used for CI engines, should be applied to SI duty cycle results to account for the HC, CO, NO_X, and PM emission increases that may occur due to enrichment AECDs.

We introduced several proposals in this section intended to achieve emission reductions without the need for manufacturers to perform additional tests. We are not proposing HD SI standards over the low load cycle or an idle test, but request comment on the need for these emission performance demonstrations in addition to or to replace our proposed procedures. We request comment on our proposed requirement that manufacturers maintain a catalyst temperature above 350 °C to ensure effective idle emission control or if an idle test procedure would be a better approach. Our proposed process to validate the accuracy of catalyst protection models is based on a 5 °C temperature allowance. We request comment on that allowance, the need for more specific procedures or technology specifications, and whether we should require continuous monitoring using temperature sensors instead of allowing the use of models. We are proposing flexibilities in OBD certifications for integrated engine manufacturers and request comment on additional flexibilities or restrictions we should consider.

E. Summary of Spark-Ignition Heavy-Duty Vehicle Refueling Emission Standards and Test Procedures

Compliance with evaporative and refueling emission standards is demonstrated at the vehicle level. The vehicle manufacturers that produce HD SI engines sell complete vehicles and, in some instances, sell incomplete vehicles to secondary manufacturers. As noted in the following section, we are proposing refueling emission standards for incomplete vehicles above 14,000 lb GVWR under both proposed Options 1 and 2. These proposed standards would apply over a useful life of 15 years or 150,000 miles, whichever occurs first, consistent with existing evaporative emission standards for these vehicles. Evaporative and refueling emission standards currently apply for complete vehicles and we are not reopening or proposing to change those requirements in this rulemaking.

1. Current Refueling Emission Standard and Test Procedures

Spark-ignition engines generally operate with volatile liquid fuel (such as gasoline or ethanol) or gaseous fuel (such as natural gas or LPG) that have the potential to release high levels of evaporative and refueling HC emissions. As a result, EPA has issued evaporative emission standards that apply to vehicles powered by these engines. Refueling emissions are evaporative emissions that result when the pumped liquid fuel displaces the vapor in the vehicle tank. Without refueling emission controls, most of those vapors are released into the ambient air. The HC emissions emitted are a function of temperature and the Reid Vapor Pressure (RVP). The emissions control technology which collects and stores the vapor generated during refueling events is the Onboard Refueling Vapor Recovery (ORVR) system.

Light-duty vehicles and chassis-certified complete heavy-duty vehicles that are 14,000 lbs GVWR and under have been meeting evaporative and refueling requirements for many years. ORVR requirements for light-duty vehicles started phasing in as part of EPA's National Low Emission Vehicle (NLEV) and Clean Fuel Vehicle (CFV) programs in 1998. In EPA's Tier 2 vehicle program, all complete vehicles with a GVWR of 8,500 to 14,000 lbs were required to phase-in ORVR requirements between 2004 and 2006 model years. In the Tier 3 rulemaking, all complete vehicles were required to meet a more-stringent standard of 0.20 grams of HC per gallon of gasoline dispensed by MY 2022 (see 40 CFR 86.1813-17(b)). Engine-certified incomplete heavy-duty vehicles that run on volatile liquid fuels have evaporative emission standards that phase in over model years 2018 through 2022, but the refueling standards were optional for incomplete vehicles.

The current evaporative and refueling emissions test procedures in 40 CFR part 1066, subpart J, require that testing occur in a sealed housing evaporative determination (SHED) enclosure containing the complete vehicle. This procedure is used by all light-duty and heavy-duty complete vehicles subject to the refueling standards, and manufacturers have designed and built the SHEDs at their test facilities for these vehicles. Since evaporative and refueling emission control systems in heavy-duty vehicles are often larger versions of those used in light-duty vehicles, EPA's regulations allow manufacturers to certify their vehicles above 14,000 lb GVWR using an engineering analysis in lieu of providing test data.

During a recent test program, EPA learned that very few SHEDs are available that could fit vehicles over 14,000 lb GVWR, as the length and height of these vehicles exceed the dimensions of most SHEDs. Additionally, the limited number of large-volume SHEDs available at third-party laboratories have challenges in accurately measuring refueling emissions because of the very large volume inside the enclosures. These measurement challenges do not currently impact manufacturers' ability to demonstrate compliance for current evaporative emissions standards because the regulations allow manufacturers to submit an engineering analysis to demonstrate compliance in lieu of testing their heavier vehicles, and currently no HD SI engine manufacturers certify complete vehicles in the over-14,000 lb GVWR vehicle class where testing is required.

2. Proposed Updates to Refueling Requirements

As HD SI engines continue to improve in their ability to reduce exhaust emissions, evaporative emissions become an increasingly significant contributor to overall HC emissions. In response to our ANPR, ORVR suppliers commented in support of refueling requirements for incomplete heavy-duty vehicles, noting the industry's experience improving, testing, and implementing the technology. We are proposing refueling emission standards for incomplete vehicles above 14,000 lb GVWR starting in model year 2027 (see 40 CFR 1037.103). We propose that these standards apply for a useful life of 15 years or 150,000 miles, whichever occurs first, consistent with the current useful life for evaporative emission standards in 40 CFR 86.1805. We are not proposing any change to the evaporative emission standards or the useful life for the evaporative standards. Since the refueling and evaporative emission standards are based on the use of similar fuel system-based technologies, it is appropriate that the useful life for the refueling standards be the same as the useful life for evaporative standards. This approach to useful life for our proposed refueling standards is consistent with the ORVR suppliers' comments.

Current refueling requirements are limited to complete vehicles, and all current heavy-duty SI engines for the over-14,000 lb GVWR vehicle classes are being certified as part of incomplete vehicles. As a result, hydrocarbon vapors from the largest HD SI engines are uncontrolled each time these vehicles are refueled. Results from a recent EPA test program found refueling emissions of more than 10 times the current light-duty ORVR standard for the two uncontrolled HD gasoline-fueled vehicles tested. ORVR systems include mature technologies that have been widely adopted in vehicles below 8,500 lb GVWR since model year 2000. As we present in our feasibility discussion in Section III.E.3.ii, the fuel systems of these larger heavy-duty engines are similar to their chassis-certified counterparts and we expect manufacturers would generally be able to scale their existing light-duty systems to meet the needs of the larger fuel tanks in their heavy-duty engine products.

i. Proposed ORVR Test Procedure and HC Standard

We are proposing a refueling emission standard of 0.20 grams HC per gallon of liquid fuel for incomplete vehicles above 14,000 lb GVWR, which is the same as the existing refueling standard for complete vehicles. We note that this proposed refueling emission standard would apply to all liquid-fueled Spark-ignition HDE, including gasoline and ethanol blends. As described in Section III.D.3, we believe it is feasible for manufacturers to achieve this standard by adopting large-scale versions of the technology in use on complete vehicles. We request comment on our proposed standard.

The current provision in 40 CFR 1037.103(c) allows vehicles above 14,000 lb GVWR to demonstrate they meet evaporative and optional refueling standards using an engineering analysis that compares the system to one certified in a full-scale SHED demonstration. We propose to continue to allow manufacturers to demonstrate they meet the proposed refueling standards using an engineering analysis, and manufacturers would continue to use this provision in light of the SHED testing challenges summarized in Section III.E.1 and in Chapter 2.3 of the draft RIA. Nonetheless, in general we continue to view full-scale, vehicle SHED testing as the most accurate representation of real world evaporative and refueling emissions and consider it the preferred means of demonstrating refueling emission control performance for certification.

We are considering updates to adapt the current test procedures to accommodate vehicles in the greater than 14,000 lb GVWR classes and to address the challenges highlighted in EPA's test program. The light-duty procedures require full-scale vehicle testing using complete vehicles in SHED enclosures. The current test procedures and most existing SHED facilities were designed to test passenger vehicles and heavy-duty complete vehicles that are much smaller than commercial vehicles in the over-14,000 lb GVWR classes. While a limited number of third-party laboratories are available with larger SHED facilities, we identified two key updates needed to accurately adapt the current refueling procedures to larger SHEDs that would fit vehicles above 14,000 lb GVWR. As discussed in Chapter 2.3 of the draft RIA, we need to extend the mixing time for the larger volume of ambient air to reach a homogeneous distribution and identify a means to accurately calculate the diverse vehicle volumes that displace air in the enclosure. We currently have limited data to inform these updates and request comment, including data, on appropriate mixing times and approaches to calculating air displacement in larger SHED enclosures. Additionally, we request comment on other aspects of the current test procedures that could be improved for evaluating vehicles above 14,000 lb GVWR.

We also request comment on the conditioning procedure to prepare the canister for testing. The current preparatory cycle used by complete HD vehicles is modeled after light-duty vehicle driving patterns and vehicles typically with much smaller fuel tanks and canisters. The current conditioning procedure is designed to challenge the purge system in scenarios such as heavy traffic, slow speeds and start-stop events over shorter drive distances and time. Heavy-duty vehicles, with larger fuel tanks and canisters, may drive more miles and longer time periods and have greater power demands that may help purge the larger canisters more easily than allowed in the current light duty vehicle test. Commercial vehicles typically experience more daily operation in traffic and on roads delivering goods but generally drive more miles and hours daily and operate under higher loads, which can accelerate the removal of vapors stored in the canister system from a diurnal or prior refueling event. We request comment on a specific canister conditioning cycle or adjustments to the current conditioning cycle that would better represent real world loading for heavy-duty vehicles entering a refueling event.

We also request comment on additional ORVR performance demonstrations EPA should consider adopting. One option would be to allow manufacturers to evaluate the entire ORVR system of an incomplete vehicle ( e.g., fuel tank, filler pipe, canister, control valves) separate from the vehicle body and chassis. Using an approach of only testing refueling components, manufacturers could use existing, widely-available chassis testing SHED enclosures, since there would no longer be a need to design expanded test cell volumes to accommodate the larger and more diverse vehicle configurations produced as incomplete vehicles. Similarly, an ORVR components test could also be performed in a smaller scale SHED (sometimes referred to as a “mini-SHED” or “rig SHED”), which is allowed by CARB for certain evaporative tests and was incorporated by reference as a phase-in option for evaporative emissions testing in our Tier 3 light-duty rulemaking. A smaller SHED enclosure provides a simpler test methodology with further reduced variability. Since testing the refueling-related components independent of the vehicle eliminates the challenge of minimizing other hydrocarbon sources not associated with fuel or the fuel system ( e.g., tires, plastics, paints), we request comment on the appropriate numeric level for the standard if evaluated using this simpler testing option, as the proposed standard is currently based on a full-vehicle test procedure. We request comment on these component-focused options or other alternatives, including specific test procedures, numeric standards, and appropriate canister conditioning cycles that we should consider to represent real world operation for these heavy-duty vehicles.

ii. Impact on Secondary Manufacturers

For incomplete vehicles above 14,000 lb GVWR, the chassis manufacturer performs the evaporative emissions testing and obtains the vehicle certificate from EPA. When the chassis manufacturer sells the incomplete vehicle to a secondary vehicle manufacturer, the chassis manufacturer provides specific instructions to the secondary manufacturer indicating what they must do to maintain the certified configuration, how to properly install components, and what, if any, modifications may be performed. For the evaporative emission system, a chassis manufacturer may require specific tube lengths and locations of certain hardware, and modifications to the fuel tank, fuel lines, evaporative canister, filler tube, gas cap and any other certified hardware would likely be limited.

We expect that the addition of any ORVR hardware and all ORVR-related aspects of the certified configuration would continue to be managed and controlled by the chassis manufacturer that holds the vehicle certificate. The engineering associated with all aspects of the fuel system design, which would include the ORVR system, is closely tied to the engine design, and the chassis manufacturer is the most qualified party to ensure its performance and compliance with applicable standards. Example fuel system changes the OEM may implement include larger canisters bracketed to the chassis frame close to the fuel tanks. Additional valves may be necessary to route the vapors to the canister(s) during refueling. Most other evaporative and fuel lines would remain in the same locations to meet existing evaporative requirements. There may be slightly different filler neck tube designs (smaller fuel transfer tube) as well as some additional tubes and valves to allow proper fuel nozzle turn-off (click off) at the pump, but this is not expected to include relocating the filler neck. Based on the comments received on the ANPR, we believe these changes would not adversely impact the secondary manufacturers finishing the vehicles.

The instructions provided by the chassis manufacturer to the secondary manufacturer to meet our proposed refueling standards should include new guidelines to maintain the certified ORVR configuration. We do not expect the new ORVR system to require significant changes to the vehicle build process, since chassis manufacturers would have a business incentive to ensure that the ORVR system integrates smoothly in a wide range of commercial vehicle bodies. Accordingly, we do not expect that addition of the ORVR hardware would result in any appreciable change in the secondary manufacturer's obligations or require secondary builders to perform significant modifications to their products.

3. Feasibility Analysis for the Proposed Refueling Emission Standards

This section describes the effectiveness and projected costs of the emissions technologies that we analyzed for our proposed refueling standards. Feasibility of the proposed refueling standard of 0.20 grams of HC per gallon is based on the widespread adoption of ORVR systems used in the light-duty and complete heavy-duty vehicle sectors. As described in this section, we believe manufacturers can effectively scale the technologies to larger engine applications to meet the proposed standard. For our inventory analysis, we assumed all heavy-duty gasoline-fueled vehicles that are identified as LHD, MHD and HHD regulatory subcategories in MOVES would implement ORVR systems starting in MY 2027 and we adjusted the refueling emission rates for those subcategories to reflect 100 percent implementation of a 0.20 grams of HC per gallon of gasoline rate in MY 2027. See Chapter 5.2.2 of the draft RIA for a discussion of our inventory model updates. The proposed refueling controls would lower refueling VOC and benzene emissions by 88.5 percent by 2045 for heavy duty gasoline vehicles over 14,000 lb GVWR. See the discussion and table in Chapter 5.3.3 of the draft RIA.

i. Summary of Refueling Emission Technologies Considered

This section summarizes the specific technologies we considered as the basis for our analysis of the proposed refueling emission standards. The technologies presented in this section are described in greater detail in Chapter 1.2.3 of the draft RIA.

Instead of releasing HC vapors into the ambient air, ORVR systems capture HC emissions during refueling events when liquid fuel displaces HC vapors present in the vehicle fuel tank as the tank is filled. These systems recover the HC vapors and store them for later purging from the system and use as fuel to operate the engine. An ORVR system consists of four main components that are incorporated into the existing fuel system: Filler pipe and seal, flow control valve, carbon canister, and purge system.

The filler pipe is the section of line from the fuel tank to where fuel enters the fuel system from the fuel nozzle. The filler pipe is typically sized to handle the maximum fill rate of liquid fuel allowed by law and integrates either a mechanical or liquid seal to prevent fuel vapors from exiting through the filler pipe to the atmosphere. The flow control valve senses that the fuel tank is getting filled and triggers a unique low-restriction flow path to the canister. The carbon canister is a container of activated charcoal designed to effectively capture and store fuel vapors. Carbon canisters are already a part of HD SI fuel systems to control evaporative emissions. Fuel systems with ORVR would require additional capacity, by increasing either the canister volume or the effectiveness of the carbon material. The purge system is an electro-mechanical valve used to redirect fuel vapors from the fuel tank and canister to the running engine where they are burned in the combustion chamber.

The fuel systems on over-14,000 lb GVWR incomplete heavy-duty vehicles are similar to those on complete heavy-duty vehicles that are currently subject to refueling standards. These incomplete vehicles may have slightly larger fuel tanks than most chassis-certified (complete) heavy-duty vehicles and are somewhat more likely to have dual fuel tanks. These differences may necessitate greater ORVR system storage capacity and possibly some unique accommodations for dual tanks ( e.g., separate fuel filler locations), as commented by ORVR suppliers in response to our ANPR.

ii. Projected Refueling Emission Technology Packages

The ORVR emission controls we projected in our feasibility analysis build upon four components currently installed on incomplete vehicles above 14,000 lb GVWR to meet the Tier 3 evaporative emission standards: The carbon canister, flow control valves, filler pipe and seal, and the purge system. For our feasibility analysis, we assumed a 70-gallon fuel tank to represent an average tank size of HD SI incomplete vehicles above 14,000 lb GVWR. A summary of the projected technology updates and costs are presented below. See Chapter 3.2 of the draft RIA for additional details.

In order to capture the vapor volume of fuel tanks during refueling, we project manufacturers would increase canister vapor or “working” capacity of their liquid-sealed canisters by 15 to 40 percent depending on the individual vehicle systems. If a manufacturer chooses to increase the canister volume using conventional carbon, we project a canister meeting Tier 3 evaporative emission requirements with approximately 5.1 liters of conventional carbon would need up to an additional 1.8 liters of carbon to capture refueling emissions from a 70-gallon fuel tank. A change in canister volume to accommodate additional carbon would result in increased costs for retooling and additional canister plastic, as well as design considerations to fit the larger canister on the vehicle. Alternatively, a manufacturer could choose to add a second canister for the extra carbon volume to avoid the re-tooling costs. We estimate projected costs for both a single larger canister and two canisters in series. Another approach, based on discussions with canister and carbon manufacturers, could be for manufacturers to use a higher adsorption carbon and modify compartmentalization within the existing shell to increase the canister working capacity. We do not have data to estimate the performance or cost of higher adsorption carbon and so did not include this additional approach in our analysis.

The projected increase in canister volumes assume manufacturers would use a liquid seal in the filler pipe, which is less effective than a mechanical seal. For a manufacturer that replaces their liquid seal with a mechanical seal, we assumed an approximate 20 percent reduction in the necessary canister volume. Despite the greater effectiveness of a mechanical seal, manufacturers in the past have not preferred this approach because it introduces another wearable part that can deteriorate, introduces safety concerns, and may require replacement during the useful life of the vehicle. To meet the proposed ORVR standards, manufacturers may choose the mechanical seal design to avoid retooling charges and we included it in our cost analysis. We assumed a cost of $10.00 per seal for a manufacturer to convert from a liquid seal to a mechanical seal. We assumed zero cost in our analysis for manufacturers to maintain their current liquid seal approach for filler pipes. While some of the largest vehicle applications with unique tank locations or designs without filler necks may need additional hardware modifications to provide enough back pressure to stop the nozzle flow and avoid spitback, we believe the cost is similar to converting to a mechanical seal, and we did not differentiate these low volume applications in our cost analysis.

In order to manage the large volume of vapors during refueling, manufacturers' ORVR updates would include flow control valves integrated into the roll-over/vapor lines. We assumed manufacturers would, on average, install one flow control valve per vehicle that would cost $6.50 per valve. And lastly, we project manufacturers would update their purge strategy to account for the additional fuel vapors from refueling. Manufacturers may add hardware and optimize calibrations to ensure adequate purge in the time allotted over the preconditioning drive cycle of the demonstration test.

Table III-34 presents the ORVR system specifications and assumptions used in our cost analysis, including key characteristics of the baseline incomplete vehicle's evaporative emission control system. Currently manufacturers size the canisters of their Tier 3 evaporative emission control systems based on the diurnal test and the Bleed Emission Test Procedure (BETP). During the diurnal test, the canister is loaded with hydrocarbons over two or three days, allowing the hydrocarbons to load a conventional carbon canister (1500 GWC, gasoline working capacity) at a 70 percent efficiency. In contrast, a refueling event takes place over a few minutes, and the ORVR directs the vapor from the gas tank onto the carbon in the canister at a canister loading efficiency of 50 percent. For our analysis, we added a design safety margin of 10 percent extra carbon to our ORVR systems. While less overall vapor mass may be vented into the canister from the fuel tank during a refueling event compared to the three-day diurnal test period, a higher amount of carbon is needed to contain the faster rate of vapor loaded at a lower efficiency during a refueling event. These factors were used to calculate the canister volumes for the two filler neck options in our cost analysis.

The assumed purge system updates are also shown in Table III-34. The diurnal drive cycle duration is 30 minutes and targets 200 bed volumes of purge to clean the canister before the evaporative emissions test. The bed volumes of purge are multiplied by the canister volume to calculate the total target purge volume. The total purge volume divided by the number of minutes driving gives us the average purge rate. An ORVR demonstration would also require conditioning of the canister in preparation for the ORVR test. The current conditioning cycle used by complete vehicles consists of a 97-minute drive cycle to prepare the canister. However, as indicated in the table, a larger target bed volume may be needed to purge the larger canister capacity required for ORVR.

The ORVR components described in this section represent technologies that we think most manufacturers would adopt to meet our proposed refueling requirements. It is possible that manufacturers may choose a different approach, or that unique fuel system characteristics may require additional hardware modifications not described here, but we do not have reason to believe costs would be significantly higher than presented here. We request comment, including data, on our assumptions related to the increased canister working capacity demands, the appropriateness of our average fuel tank size, the technology costs for the specific ORVR components considered and any additional information that can improve our cost projections in the final rule analysis.

iii. Summary of Costs To Meet the Proposed Refueling Emission Standards

Table III-35 shows cost estimations for the different approaches evaluated. In calculating the overall cost of our proposed program, we used $25, the average of both approaches, to represent the cost for manufacturers to adopt the additional canister capacity and hardware to meet our proposed refueling emission standards for incomplete vehicles above 14,000 lb GVWR. See Section V of this preamble for a summary of our overall program cost and Chapter 7 of the draft RIA for more details.

Incomplete vehicles above 14,000 lb GVWR with dual fuel tanks may require some unique accommodations to adopt ORVR systems. A chassis configuration with dual fuel tanks would need separate canisters and separate filler pipes and seals for each fuel tank. Depending on the design, a dual fuel tank chassis configuration may require a separate purge valve for each fuel tank. We assume manufacturers would install one additional purge valve for dual fuel tank applications that also incorporate independent canisters for the second fuel tank/canister configuration and manufacturers adopting a mechanical seal in their filler pipe would install an anti-spitback valve for each filler pipe. See Chapter 1.2.4.5 of the draft RIA for a summary of the design considerations for these fuel tank configurations. We did not include an estimate of the population or impact of dual fuel tank vehicles in our cost analysis of our proposed refueling emission standards.

4. Summary of Requests for Comment

We are requesting comment regarding the cost, feasibility, and appropriateness of our proposed refueling emission standard for incomplete vehicles above 14,000 lb GVWR. The proposed standard is based on the current refueling standard that applies to complete heavy-duty gasoline-fueled vehicles. We are proposing that compliance with these standards may be demonstrated under an existing regulatory provision by using an engineering analysis due to uncertainties related to testing these larger vehicles. We request comment on approaches to adapt the current test procedures used by lower GVWR vehicles for vehicles above 14,000 lb GVWR. Specifically, we are interested in comments including data or established procedures to calculate appropriate mixing times and air displacement in larger SHED enclosures. We also request comment on the appropriate conditioning procedure for these larger vehicles. Finally, we request comment on other testing options we should consider for manufacturers to demonstrate the effectiveness of their ORVR systems on incomplete vehicles above 14,000 lb GVWR.

IV. Compliance Provisions and Flexibilities

EPA certification is a fundamental requirement of the Clean Air Act for manufacturers of heavy-duty highway engines. EPA has employed significant discretion over the past several decades in designing and updating many aspects of our heavy-duty engine and vehicle certification and compliance programs. In the following sections, we discuss several proposed provisions that we believe would increase the effectiveness of our regulations, including some opportunities to streamline existing requirements. Unless explicitly stated otherwise, the proposed provisions in this Section IV would apply to proposed Options 1 and 2, as well as the full range of options in between them.

As noted in Section I, we are proposing to migrate our criteria pollutant regulations for model years 2027 and later heavy-duty highway engines from their current location in 40 CFR part 86, subpart A, to 40 CFR part 1036. Consistent with this migration, the proposed compliance provisions discussed in this section refer to the proposed regulations in their new location in part 1036. In general, this migration is not intended to change the compliance program previously specified in part 86, except as specifically proposed in this rulemaking. See our memorandum to the docket for a detailed description of the proposed migration.

A. Regulatory Useful Life

In addition to emission standards and test procedures discussed in Section III, appropriate regulatory useful life periods are critical to assure emission performance of heavy-duty highway engines. Our regulations require manufacturers to perform durability testing to demonstrate that engines will meet emission standards not only at certification but also over the full useful life periods specified by EPA. Useful life represents the period over which emission standards apply for certified engines, and, practically, any difference between the regulatory useful life and the generally longer operational life of in-use engines represents miles and years of operation without an assurance that emission standards will continue to be met.

In this section, we describe our estimates of the length of operational lives of heavy-duty highway engines, which are almost double the current useful life mileages in EPA's regulations for all primary intended service classes. EPA is proposing to increase the regulatory useful life mileage values for new heavy-duty engines to better reflect real-world usage, extend the emissions durability requirement for heavy-duty engines, and improve long-term emission performance. Our proposed longer useful life periods for heavy-duty engines vary by engine class to reflect the different lengths of their estimated operational lives. As described in Section III, the proposed numeric levels of the standards are the same across engine classes and are based on the feasibility of achieving those standards at the proposed useful life mileages. Proposed Option 1 useful life periods would apply in two steps in MY 2027 and MY 2031 and proposed Option 2 useful life periods would apply in a single step in MY 2027.

For CI engines, the proposed Option 1 useful life mileage values for MY 2031 and later are based on data on the average periods to the first out-of-frame rebuild for these engines. Our CI engine demonstration, which is based on the emission performance of an engine in the Heavy HDE class, projects the engine can achieve the proposed standards for MY 2031 at the proposed useful life mileage. Our demonstration data does not currently show that it is feasible to achieve the proposed Option 1 MY 2027 standards at the MY 2031 useful life mileages, and the proposed Option 1 useful life mileage values for MY 2027 through 2030 are approximately a midpoint between the current useful life mileages and our proposed Option 1 MY 2031 and later mileages.

Similarly, the proposed Option 1 would increase useful life mileages in two steps for the proposed standards for heavy-duty SI engines that are not chassis-certified. Our proposed Option 1 first step for these SI engines in MY 2027 through 2030 would better align with the current useful life mileages for GHG emission standards applicable to these engines and for chassis-certified complete vehicles containing these engines. The proposed Option 1 second step for these SI engines in MY 2031 and later would be based on the expected engine service life for heavy-duty gasoline engines in the market today. The SI demonstration program showed that the proposed Option 1 standards are feasible over the proposed Option 1 useful life mileages.

In our ANPR, we presented CI engine rebuild data and noted that we intended to propose useful life mileage values for all categories of heavy-duty engines that are more reflective of real-world usage. Comments received on the ANPR included varied support for increasing engine useful life values. Environmental organizations and state, local, and Tribal air agencies largely supported lengthened useful life, and many supported aligning with CARB's HD Omnibus rulemaking. Among the sixteen state, local, and Tribal governments and related associations that expressed support, the National Tribal Air Association stated that longer useful life requirements would lead to longer design life targets for emissions systems commensurate with actual vehicle service lengths. The International Council on Clean Transportation (ICCT) commented that EPA should harmonize useful life requirements with California and stated that it could be possible to double the useful life of the emission control systems with available technologies.

Other commenters expressed cautious support. The Manufacturers of Emission Controls Association (MECA) and Motor and Equipment Manufacturers Association (MEMA) supported extending useful life with a phased approach that allows suppliers time to design, test, and address issues with their components' durability beyond today's requirements. Several commenters expressed concern related to the cost of extending longer useful life periods. The American Truck Dealers Division of the National Automobile Dealers Association (NADA) stated that longer useful life periods may be warranted given the increasing number of miles heavy-duty engines accumulate prior to engine rebuild. NADA asked EPA to carefully assess higher up-front engine costs associated with longer useful life periods and the potential for reduced maintenance and repair costs resulting from increased useful life. Volvo stated that more durable components are not available “to pull from the shelf” and costs to extend the life of those components could result in significant costs either to improve the components or incorporate a replacement as part of the manufacturer's scheduled maintenance. Volvo also expressed concern that second and third owners may use the vehicles for applications that could stress the engine and its systems and threaten emissions compliance within a lengthened useful life. The Truck and Engine Manufacturers Association (EMA) and Cummins commented that EPA should carefully evaluate the benefits of extending the useful life period. EMA stated a longer useful life could require the replacement of aftertreatment systems during the lengthened period.

We note that as manufacturers develop compliance strategies to meet our proposed emission standards and lengthened useful life periods, they have the ability to design for increased durability of their engine and emission controls and to create maintenance instructions describing how to clean, repair, or replace emission components at specified intervals subject to the limitations in our proposed maintenance provisions. To address the feasibility of meeting the proposed standards over the proposed useful life periods, the technology demonstration projects described in Section III of this preamble include demonstrating the durability and emissions performance of CI and SI engines over mileages that cover the range of useful life mileages being considered. We believe our proposed useful life periods are feasible and would not require manufacturers to adopt component replacement as part of their critical emission-related maintenance strategies.

1. History of Regulatory Useful Life

The Clean Air Act specifies that emission standards under section 202(a) “shall be applicable to such vehicles and engines for their useful life . . . whether such vehicles and engines are designed as complete systems or incorporate devices to prevent or control such pollution.” Practically, this means that to receive an EPA certificate of conformity under the CAA, a manufacturer must demonstrate that an engine or vehicle, including the aftertreatment system, will meet each applicable emission standard, including accounting for deterioration, over the useful life period specified in EPA's regulations. In addition, CAA section 207(c) requires manufacturers to recall and repair vehicles or engines if the Administrator determines that “a substantial number of any class or category of vehicles or engines, although properly maintained and used, do not conform to the regulations prescribed under [section 202(a)], when in actual use throughout their useful life (as determined under [section 202(d)]).” Taken together, these sections define two critical aspects of regulatory useful life: (1) The period over which the manufacturer must demonstrate compliance with emissions standards to obtain EPA certification, and (2) the period for which the manufacturer is subject to in-use emissions compliance liability, e.g., for purposes of recall. Manufacturers perform durability testing to demonstrate that engines will meet emission standards over the full useful life. Manufacturers may perform scheduled maintenance on their test engines only as specified in the owner's manual. As part of the certification process, EPA approves such scheduled maintenance, which is also subject to minimum maintenance intervals as described in the regulation. See Section IV.F for a description of the current and proposed durability requirements and Section IV.B.5 for more information on our current and proposed maintenance provisions. Manufacturer obligations under recall are specified in 40 CFR 1068, subpart F, and we are not proposing to update our recall provisions.

EPA prescribes regulations under CAA section 202(d) for determining the useful life of vehicles and engines. CAA section 202(d) provides that the minimum useful life for heavy-duty vehicles and engines is a period of 10 years or 100,000 miles, whichever occurs first. This section authorizes EPA to adopt longer useful life periods that we determine to be appropriate. Under this authority, we established useful life periods for heavy-duty engines by primary intended service class. As introduced in Section I, heavy-duty highway engine manufacturers identify the primary intended service class for each engine family by considering the vehicles for which they design and market their engines. Heavy-duty compression-ignition engines are distinguished by their potential for rebuild and the weight class of the final vehicles in which the engines are expected to be installed. Heavy-duty spark-ignition engines are generally classified as a single “spark-ignition” service class unless they are designed or intended for use in the largest heavy-duty vehicles and are thereby considered heavy heavy-duty engines.

The following useful life periods currently apply to the criteria pollutant emission standards for heavy-duty highway engines:

• 110,000 miles or 10 years for heavy-duty spark-ignition engines and light heavy-duty compression-ignition engines
• 185,000 miles or 10 years for medium heavy-duty compression-ignition engines
• 435,000 miles, 10 years, or 22,000 hours for heavy heavy-duty compression-ignition engines

In our 1983 rulemaking, which first established class-specific useful life values for heavy-duty engines and vehicles, EPA adopted the principle that useful life mileage values should reflect the typical mileage to the first rebuild of the engine (or scrappage of the engine if that occurs without rebuilding). Significantly, this approach was adopted at a time when diesel engine emission control strategies relied mainly on in-cylinder engine combustion controls.

Over time, mileage values became the primary metric for useful life duration. This is because, due to advancements in general engine durability, nearly all heavy-duty engines reach the mileage value in-use long before 10 years have elapsed. The age (years) value has meaning for only a small number of low-annual-mileage applications, such as refuse trucks. Also, manufacturer durability demonstrations generally target the mileage values, since deterioration is a function of engine work and hours rather than years in service and a time-based demonstration would be significantly longer in duration than one based on applicable mileage value.

In the 1997 rulemaking that most recently increased heavy-duty engine useful life, EPA included an hours-based useful life of 22,000 hours for the heavy heavy-duty engine intended service class. This unique criterion was added to address the concern that urban vehicles, particularly urban buses, equipped with heavy heavy-duty engines had distinctly different driving patterns compared to the line-haul trucks from which the agency based its useful life value of 435,000 miles. Commenters in that rulemaking indicated that urban bus average speed was near 13 miles per hour. Considering that speed, many of these bus engines would reach the end of their operational life or be candidates for rebuild before the applicable mileage value or the 10-year criterion is reached. The 22,000 hours value was adopted in lieu of a proposed minimum useful life value of 290,000 miles for heavy heavy-duty engines. Considering the current 435,000 useful life mileage for heavy heavy-duty engines, the 22,000-hour useful life value only has significance for the small subset of vehicles equipped with heavy heavy-duty engines with an average speed of less than 20 miles per hour.

In the Phase 1 GHG rulemaking, we promulgated useful life periods for the GHG emission standards for heavy-duty highway engines and their corresponding heavy-duty vehicles that aligned with the current useful life periods for criteria pollutant emission standards. In the HD Phase 2 GHG rulemaking, we extended the useful life for Light HDV, light heavy-duty engines, and spark-ignition engines for the GHG emission standards to 15 years or 150,000 miles to align with the useful life of chassis-certified heavy-duty vehicles subject to the Tier 3 standards. See 40 CFR 1036.108 and 40 CFR 1037, subpart B, for the GHG useful life periods that apply for heavy-duty highway engines and vehicles, respectively. We are not proposing changes to the useful life periods for GHG emission standards in this rulemaking.

2. Identifying Appropriate Useful Life Periods

Emission standards apply for the engine's useful life and manufacturers must demonstrate the durability of engines to maintain certified emission performance over their useful life. Thus, the proposed emission standard options presented in Section III must be considered together with their associated proposed useful life periods. Larger useful life mileage values would require manufacturers to demonstrate emission performance over a longer period and should result in effective emission control over a greater proportion of an engine's operational (sometimes referred to as “service”) life. Consistent with our approach to adopting useful life mileages in the 1983 rulemaking, we continue to consider a comprehensive out-of-frame rebuild to represent the end of a heavy-duty CI engine's “first life” of operation. For SI engines that are less commonly rebuilt, engine replacement would be a more appropriate measure of an engine's operational life. Our proposed Option 1 useful life values are based on the expected operational life of the engine or, for CI engines, an estimate of the point at which an engine is typically rebuilt. We expand on this approach in the following sections. We discuss the basis of proposed Option 2 useful life values in Section IV.A.3.

i. Compression-Ignition Engine Rebuild Data

In 2013, EPA commissioned an industry characterization report on heavy-duty diesel engine rebuilds. The report relied on existing data from MacKay & Company surveys of heavy-duty vehicle operators. In this report, an engine rebuild was categorized as either an in-frame overhaul (where the rebuild occurred while the engine remained in the vehicle) or an out-of-frame overhaul (where the engine was removed from the vehicle for more extensive service). The study showed that the mileage varied depending on the type of rebuild. Rebuilding an engine while the block remained in the frame was typically done at lower mileage than rebuilding an engine removed from the vehicle. The results of the study by vehicle weight class are presented in Table IV-1.

McKay & Company does not collect information on aftertreatment systems ( e.g., diesel oxidation catalysts, SCR systems, or three-way catalysts), so neither EPA's 2013 report nor CARB's more recent report for their HD Omnibus rulemaking include aftertreatment system age information. We consider the mileage at rebuild or replacement of an engine to represent the operational life of that engine, including any aftertreatment components that were part of its original certified configuration. We have no data to indicate aftertreatment systems lose functionality before engines are rebuilt or replaced, and our technology demonstrations in Section III show aftertreatment catalysts are able to maintain performance when bench-aged to beyond the equivalent of current useful life mileages.

We averaged the mileages for these vehicle classes according to EPA's primary intended service classes for heavy-duty CI engines as defined in 40 CFR 1036.140. Specifically, we averaged Classes 3, 4, and 5 to represent Light HDE, Classes 6 and 7 to represent Medium HDE, and Class 8 to represent Heavy HDE. These values are shown in Table IV-2 with the current useful life mileages that apply to each intended service class. As seen in the tables, the study reported typical engine rebuild mileages that are more than double the current useful life mileages for those classes.

We note that Light HDE intended for smaller vehicle classes are not designed with cylinder liners to facilitate rebuilding, suggesting they are more likely to be scrapped at the end of their operational life. The rebuilding report notes that seven percent of the diesel-fueled engines in the 2012 Class 3 vehicle population were removed from the vehicle to be rebuilt, but does not include data on the corresponding number of engines or vehicles scrapped in that year. We assume the mileage at which an engine has deteriorated enough to consider rebuilding would be similar to the mileage of an engine eligible for scrappage and both similarly represent the operational life of an engine for the purpose of this analysis.

ii. Spark-Ignition Engine Service Life Data

The useful life mileage that applies for GHG emission standards for Spark-ignition HDE is 150,000 miles, which is longer than the current useful life of 110,000 miles for criteria pollutant emission standards for those same engines. For our proposed Option 1 updates to the useful life for Spark-ignition HDE criteria pollutant emission standards, we considered available data to represent the operational life of recent heavy-duty SI engines. A review of market literature for heavy-duty gasoline engines showed that at least one line of engine-certified products is advertised with a service life of 200,000 miles. Compliance data for MY 2019 indicate that the advertised engine model represents 20 percent of the Spark-ignition HDE certified for MY 2019. Additionally, CARB's HD Omnibus rulemaking cited heavy-duty Otto-cycle engines ( i.e., Spark-ignition HDE) for vehicles above 14,000 lb GVWR that were replaced during calendar years 2012 through 2018 as reaching more than 217,000 miles on

average. The mileages in these two examples are almost double the current useful life for Spark-ignition HDE, indicating many miles of operation beyond the current useful life.

iii. CARB HD Omnibus Useful Life Values

The CARB HD Omnibus rulemaking, finalized in August 2020, lengthens useful life for heavy-duty CI and SI engines in two steps. As part of their rule, CARB analyzed recent MacKay & Company survey data from calendar years 2012 through 2018 and reported rebuild mileages for CI engine categories that were similar to those described in the Section IV.A.2.i. CARB also included average replacement mileage information for heavy-duty Otto-cycle (HD SI) engines. The CARB/MacKay & Company data is summarized in Table IV-3.

Although the CARB HD Omnibus program begins in MY 2024, the program maintains the current useful life values through MY 2026. Table IV-4 summarizes the useful life values finalized in the HD Omnibus rule for heavy-duty Otto-cycle engines (HDO), and light heavy-duty diesel (LHDD), medium heavy-duty diesel (MHDD), and heavy heavy-duty diesel (HHDD) engines.

As seen in the table, CARB's Omnibus increases useful life first in MY 2027 with a second step in MY 2031. The final useful life mileages in the CARB regulation are the result of stakeholder engagement throughout the development of CARB's HD Omnibus rulemaking. In two 2019 public workshops, CARB staff presented useful life mileage values under consideration that were longer than these final mileages and, in their September 2019 presentation, very close to the engine rebuild mileages. In response to feedback from stakeholders indicating concerns with availability of data for engines and emission controls at those mileages, CARB shortened their final useful life mileages for MY 2031 and later engines from the values presented in 2019, and the MY 2027 values were chosen to be approximately the mid-point between the current and final useful life mileages. Additionally, CARB finalized an intermediate useful life mileage for MY 2027 and later HHDD engines that correspond to the current useful life of 435,000 miles. See Section III.B for a discussion of the standards at the intermediate and full useful life mileages. Consistent with current useful life periods, CARB finalized hours values for the HHDD engine class based on the useful life mileage and an average vehicle speed of 20 miles per hour.

Similar to the useful life mileage values, CARB's useful life values in years were also adjusted from the values presented in their public workshops based on stakeholder feedback. In particular, emission controls manufacturers recommended CARB consider replacing the 18-year useful life presented in their September 2019 workshop with a useful life of 12 years for heavy-duty engines. CARB agreed that 12 years was reasonable for MHDD and HHDD, but adopted a 15 year useful life for HDO and LHDD based on the useful life in years that applies to chassis-certified engines.

3. Proposed Regulatory Useful Life Periods

In this section, we introduce our proposed regulatory useful life periods for heavy-duty highway engines as specified in the new 40 CFR 1036.104(e). Our CI and SI engine technology demonstrations in Section III support our conclusion that it is feasible for manufacturers to meet our proposed standards for the proposed useful life periods of Options 1 and 2. We note that our technology demonstrations rely on an accelerated aging process for the catalyst-based aftertreatment systems and we are proposing to update our durability demonstration provisions to allow manufacturers to similarly accelerate the aging of their catalysts for certification. See Section IV.F for a description of our durability demonstration proposal.

We are proposing useful life mileage and years values for all primary intended service classes that are based on our current estimate of the operational lives of the engines in those classes. The useful life values described in this section apply for exhaust emission standards for criteria pollutants, as well as evaporative and refueling emission standards, OBD, and requirements related to crankcase emissions. Proposed Option 1 includes an hours specification for the Heavy HDE class, which has the longest useful life mileages, to address vehicles that frequently operate at idle or lower speeds. The proposed Option 1 useful life periods generally align with those in the CARB HD Omnibus regulation. We request comment on our proposal, including whether it is appropriate to fully harmonize the federal and CARB regulatory useful life periods in light of the authority and requirements of section 202, and any concerns if EPA were to finalize values that are or are not aligned with CARB for a given engine class or range of model years.

i. Proposed Useful Life by Primary Intended Service Class

Data indicate heavy-duty highway engines remain on the road well beyond the current regulatory useful life periods and compliance with emission standards is uncertain for a large portion of engine operational lives today. We are proposing to lengthen the useful life periods to cover a larger fraction of the operational life of these engines. Our proposed useful life periods for Spark-ignition HDE, Light HDE, Medium HDE, and Heavy HDE classes are presented in Table IV-5 and specified in a proposed new 40 CFR 1036.104(e). In Section III, we discuss the feasibility of meeting the emission standards at the useful life values of proposed Options 1 and 2. In Section IV.A.4, we introduce an alternative set of useful life periods we considered in addition to our proposed values as part of our feasibility analysis.

We consider a comprehensive out-of-frame rebuild to represent the end of a heavy-duty CI engine's “first life” of operation. The proposed Option 1 useful life periods for all engine classes align with the final values adopted by CARB in their HD Omnibus regulation and cover a larger fraction of the expected operational lives of these engines. Consistent with previous rulemakings, we believe we could justify proposing useful life requirements equivalent to the operational life data presented in Section IV.A.2, but are proposing somewhat shorter (less stringent) values in proposed Option 1 considering the effect of useful life on the feasibility of meeting the proposed Option 1 standards. The useful life mileages of proposed Option 2 generally correspond to the average mileages at which CI engines undergo the first in-frame rebuild as described in Section IV.A.2.i. At these mileages, CI engine owners could be expected to replace some critical components, but would be able to accrue many additional miles before a comprehensive rebuild. The out-of-frame rebuild data indicates that these engines can last well beyond the in-frame rebuild mileages, and we are unlikely to finalize a single step program with useful life mileages that are lower than proposed Option 2.

For SI engines that are less commonly rebuilt, engine replacement more appropriately marks the end of its operational life. The estimated operational life data presented in Section IV.A.2 indicate that heavy-duty highway engines can operate for nearly double their current regulatory useful lives. As described in Section III, our SI engine demonstration program evaluated emission performance at an equivalent 250,000 miles (beyond the SI HDE service life and replacement mileage information presented in Section IV.A.2). Emission results from our demonstration program were lower than the proposed Option 1 MY 2031 standards for all pollutants on the FTP duty cycle, and for all but CO on the SET duty cycle. We project the proposed Option 1 MY 2031 CO standard would be met by optimizing emission control calibrations. For Option 1, we are proposing a MY 2031 useful life of 200,000 miles (50,000 miles shorter than the equivalent mileage of the engine in our demonstration program), which we believe would ensure the proposed Option 1 MY 2031 standards are feasible for Spark-ignition HDE. For Option 1, we are proposing shorter useful life mileages along with the less stringent proposed Option 1 standards for MY 2027 to allow manufacturers appropriate time to prepare their engines to meet standards on the proposed new SET cycle, adopt our proposed idle controls, and address other proposed compliance requirements. For SI engines, the useful life mileage in proposed Option 2 aligns with the current useful life mileage that applies for these engines for GHG standards and represents the lowest useful life mileage we are currently considering for Spark-ignition HDE. Commenters supporting the SI engine useful life mileages for proposed Option 2 are encouraged to provide data, since proposed Option 2 useful life mileages currently apply for GHG standards and our SI engine test program has demonstrated most of the proposed standards are achievable well beyond the proposed Option 2 mileage.

Our CI engine demonstration evaluated emissions at mileages that correspond to the Light HDE and Medium HDE operational life mileages presented, and we continue to evaluate higher mileages that would cover a greater portion of the operational life of Heavy HDE. The uncertainty of emission performance at mileages close to Heavy HDE rebuild mileages, coupled with the lack of aftertreatment performance information in the rebuild data, has led us to propose Option 1 MY 2031 useful life mileages that cover a majority of the estimated operational life mileages, but less than the full rebuild mileages presented in Section IV.A.2. Since the EPA rebuild mileages are similar to the rebuild mileages in CARB's recent rebuild analysis, we are proposing CI HDE useful life mileages that align with CARB.

We request comment on the proposed approach to base these mileages on the data presented. We request additional data to inform our consideration of appropriate useful life mileages, including rebuilding, replacement, and scrappage data, or other data that may represent the operational life of a heavy-duty highway engine. We also request comment on what portion of an engine's operational life should be covered by the regulatory useful life and whether it should depend on specific characteristics of the engine ( e.g., primary intended service class).

As seen in Table IV-5, our proposed Option 1 would increase the years-based useful life values intended to address engines that accumulate fewer miles annually. Our proposed increased useful life in years for Option 1 would also occur in two steps that align with the values finalized in CARB's HD Omnibus regulation. Proposed Option 1 would increase Heavy HDE and Medium HDE useful life years to 11 years in MY 2027 and 12 years in MY 2031. The 12-year useful life value is consistent with the recommendation by MECA. Proposed Option 1 would also increase Spark-ignition and Light HDE useful life years to 12 years in MY 2027 and 15 years in MY 2031. A 15-year useful life value would be consistent with the existing useful life in years for these engines for GHG emission standards. We propose to maintain the existing years-based useful life of 10 years for all primary intended service classes under proposed Option 2.

Proposed Option 1 also includes updates to the hours-based useful life criteria for the Heavy HDE class to align with the proposed mileage steps. Historically, EPA included a unique hours specification for the Heavy HDE class to account for engines that operated frequently, but accumulated relatively few miles due to lower vehicle speeds. The 22,000-hour useful life value that currently applies for Heavy HDE corresponds to an average vehicle speed of 20 miles per hour.

Consistent with our original approach to defining an hour-based useful life value, we are proposing to update the useful life hours of operation value for the Heavy HDE primary intended service class based on a 20 mile per hour speed threshold and the proposed useful life mileages. For model year 2027 through 2030 Heavy HDE in Option 1, we propose a useful life period of 11 years, 600,000 miles, or 32,000 hours, whichever comes first. Similarly, for model year 2031 and later Heavy HDE in Option 1, we propose 12 years, 800,000 miles, or 40,000 miles, whichever comes first.

We request comment on the need for a useful life hours criterion for Heavy HDE and whether we should include one for other primary intended service classes. If we were to include a useful life hours criterion for other or all heavy-duty highway engines, we request comment whether to use a speed other than 20 miles per hour for engines intended for lower GVWR class vehicles.

We are proposing not to migrate paragraph (4)(iv) from the existing definition of “useful life” in 40 CFR 86.004-2 to proposed 40 CFR 1036.104. It is our understanding that all modern ECMs contain time counters, so it is reasonable to assume that manufacturers can reliably access that information to document an engine's hours of operation and the requirement for an “accurate hours meter” is unnecessary. We request comment on the need to include an accurate hours meter requirement as part of a useful life hours criterion in part 1036.

As introduced in Section III.A.1, we are proposing to clarify how hybrid engines and powertrains can certify they meet criteria pollutant regulations, which includes demonstrating that they meet emission standards throughout the regulatory useful life. We propose that manufacturers certifying hybrid engines and powertrains declare the primary intended service class of their engine family using 40 CFR 1036.140, which is partially based on the GVWR of the vehicle in which the engine configuration is intended to be used. Once a primary intended service class is declared the engine configuration would be subject to the corresponding emission standards and useful life values from 40 CFR 1036.104(e). Our proposed approach to clarify that hybrid components could be part of an engine configuration provides truck owners and operators with consistent assurance of durability based on the intended vehicle application. Our proposed approach is similar to the CARB Omnibus rule requirements for hybrid powertrains to meet useful life based on primary intended service class, though we are proposing flexibility for manufacturers to identify the appropriate service class for their engine configurations.

Our proposal does not mean that a specific component of the certified configuration, such as a hybrid battery, is required to last the full useful life indicated by its primary intended service class. Manufacturers continue to have options to address the repair or replacement of components within the useful life, both in the durability demonstration for certification and in-use, as specified in the maintenance provisions of 40 CFR 1036.125. See Section IV.B.5 for a discussion of our proposals related to maintenance. We request comment on our proposed approach for manufacturers certifying hybrid engines and powertrains to declare a primary intended service class and meet the corresponding emission standards and useful life periods.

ii. Proposed Useful Life for Heavy-Duty Electric Vehicles

As discussed in Section III.A, we are proposing clarifications and updates to our regulations for heavy-duty electric vehicles, including battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). Our proposal clarifies how the proposed useful life provisions for criteria pollutant emission standards would apply to each of these types of electric vehicles. Immediately below, we discuss the specifics and rationale of our proposed approach to useful life periods for BEVs and FCEVs. Additional information on our proposal and requests for comment are included in the following subsections: IV.B.1.iv.b (BEV and FCEV warranty requirements), IV.B.3.iii (request for comment on maintenance and operational information to improve electric vehicle serviceability), and IV.I (compliance options for generating NO_X emission credits from electric vehicles).

As noted in Section III.A and discussed in Section IV.I, we are proposing a change from our current approach under 40 CFR 86.016-1(d)(4) that would allow manufacturers to generate NO_X emission credits from BEVs and FCEVs starting in MY 2024, as specified in the proposed 40 CFR 1037.616, if they conduct testing and meet durability requirements in the proposed 40 CFR 1037.102(b). We propose that manufacturers who choose to generate NO_X emission credits from BEVs or FCEVs would certify to the emission standards and useful life values of an engine-based primary intended service class, as specified in proposed 40 CFR 1037.102(b). Proposed 40 CFR 1037.102(b) specifies that for MYs 2024 through 2026, manufacturers choosing to generate NO_X emission credits from BEVs or FCEVs would apply the useful life periods in current 40 CFR 86.001-2; starting in MY 2027 manufacturers would apply the useful life periods in proposed 40 CFR 1036.104. We also propose that starting in MY 2027, manufacturers who choose not to generate NO_X emission credits from BEVs or FCEVs could alternatively choose to certify to a shorter useful life period that is the same as those for GHG emissions standards for the appropriate service class in the current 40 CFR 1037.105(e).

Manufacturers who choose not to generate NO_X emission credits from BEVs or FCEVs may choose to attest that their vehicle complies with the standards in proposed 40 CFR 1037.102 instead of submitting test data for MY 2027 and later, as specified in the proposed 40 CFR 1037.205(q)(1). Manufacturers who choose to generate NO_X emission credits from BEVs or FCEVs as early as MY 2024 may also attest that their BEV or FCEV meets the durability requirements described in proposed 40 CFR 1037.102(b)(3) based on an engineering analysis of measured values and other information, consistent with good engineering judgment, instead of testing at the end of the useful life; however they would also be required to submit additional information as specified in the proposed 40 CFR 1037.205(q)(2) and discussed in Section IV.I.

The purpose of requiring BEV and FCEV manufacturers who choose to generate NO_X emission credits to meet durability requirements is to ensure that manufacturers design the BEV and FCEV products to be at least as durable as the engine products that would rely on the NO_X emission credits to comply with applicable NO_X standards. Since manufacturers would be able to use NO_X emissions credits from BEVs or FCEVs to produce other engines with NO_X emissions above the proposed standards for MYs 2027 and later, we believe it is imperative that these technologies provide zero-tailpipe emission performance throughout the useful life period to which they certify and for which they generate NO_X emission credits. This approach would help to ensure that these zero-tailpipe emission technologies can operate for the same periods as the engine products that rely on the NO_X emission credits. We also note that data from transit buses show BEVs are capable of operating more than 10 million miles and over 30 years of normal service in a typical transit bus duty-cycle. Similarly, the DOE has set heavy-duty FCEV durability target at 1 million miles by 2030. Both the transit bus data and DOE target support BEV and FCEVs technologies being capable of meeting the useful life requirements of proposed Options 1 and 2 for CI engines in the 2027 and beyond timeframe. Nevertheless, we recognize that BEV and FCEV technologies, and the batteries and fuel cells that power them, are still developing; thus, we propose to allow BEV and FCEV manufacturers not participating in the NO_X engine ABT program to certify to criteria pollutant useful life requirements that are equivalent to the current requirements for certifying to the GHG emission standards.

We request comment on our proposal to align BEV and FCEV useful life periods with those for an engine-based service class for manufacturers who choose to generate NO_X emission credits. We further request comment on allowing manufacturers who choose not to generate NO_X emission credits from BEVs or FCEVs to certify to criteria pollutant useful life periods that are equivalent to the current useful life periods for the GHG emission standards. We are also interested in other approaches identified or recommended by commenters. Commenters are encouraged to provide data on current BEV and FCEV durability, as well as any additional information EPA should consider when setting useful life periods and related requirements for BEVs and FCEVs in the final rulemaking.

iii. Proposed Useful Life for Incomplete Vehicle Refueling Emission Standards

As described in Section III.E., proposed Options 1 and 2 include refueling standards for incomplete vehicles above 14,000 lb GVWR. Manufacturers would meet the proposed refueling emission standards by installing onboard refueling vapor recovery (ORVR) systems. ORVR systems are based on the same carbon canister technology that manufacturers currently use to control evaporative emissions on these incomplete vehicles. Since both the evaporative and refueling emission control systems are part of the same fuel system, and due to the similarity of many of the components, we propose to align the useful life periods for the two systems (see our proposed updates to 40 CFR 1037.103(f)). Specifically, proposed Options 1 and 2 include a useful life of 15 years or 150,000 miles, whichever comes first, for refueling standards for incomplete vehicles above 14,000 lb GVWR.

Evaporative emission control systems are currently part of the fuel system of incomplete vehicles, and manufacturers are meeting applicable standards and useful life requirements for these systems today. ORVR is a mature technology that has been installed on complete vehicles for many years, and incomplete vehicle manufacturers have experience with ORVR systems through their complete vehicle applications. Considering the manufacturers' experience with evaporative emission standards for incomplete vehicles, and their familiarity with ORVR systems, we believe it would be feasible for manufacturers to apply the same evaporative emission standard useful life periods to our proposed refueling standards.

We request comment on our proposal to align the useful life for refueling standards with the existing useful life periods for evaporative emission standards and whether we should instead consider aligning with the broader useful life periods proposed for Spark-ignition HDE ( e.g., the proposed Option 1 useful life periods of 12 years/155,000 miles for MY 2027 through 2030 and 15 years/200,000 miles for MY 2031 and later), or whether we should take another approach. We also request comment on the need for a transitional useful life step for refueling standards for MY 2027 through 2030, including concerns with component durability or testing that would require additional lead time to address. Commenters are encouraged to include ORVR system data at their recommended useful life values. Finally, we request comment on any concerns about having different useful life values for refueling standards compared to the useful life values for either evaporative emission standards or Spark-ignition HDE standards.

4. Potential Alternative Useful Life Mileages

We considered an alternative set of useful life mileages (Alternative), which would each apply in a single step beginning in MY 2027. Table IV-6 presents a comparison of the current useful life mileages and the useful life mileages of the proposed Options and Alternative.

The useful life mileages that we considered in the Alternative are longer than the proposed Option 1 MY 2031 useful life mileages. The useful life mileages of this alternative match those presented in CARB's September 2019 Public Workshop for their Heavy-Duty Low NO_X program as early CARB staff-level thinking; these draft mileages were then lowered in the 2020 Omnibus program approved by CARB governing board. While the CI engine mileages for the Alternative are closer to the average mileage at which most CI engines undergo an out-of-frame rebuild, currently available data indicate that the Alternative standards presented in Section III would be very challenging to meet at those useful life mileages for Light HDEs and Medium HDEs, and thus data suggest that it may be appropriate for EPA to consider providing manufacturers with additional lead time, beyond the MY 2027 implementation date of the Alternative. For Heavy HDEs, our extrapolation of the data from 435,000 miles through the 850,000 mile useful life of the Alternative suggests that the numeric level of the NO_X emission control in the Alternative could not be maintained through the Alternative useful life period (see Section III for details).

The SI mileage for the Alternative represents the equivalent mileage of the bench-aged three-way catalyst used in the SI technology demonstration for this rulemaking, but currently available data suggest it would be very challenging to achieve the standards of this alternative for all pollutants in the MY 2027 timeframe. For both CI and SI engines, we would need additional data to be able to conclude that the standards combined with the useful mileages included in the Alternative are feasible in the MY 2027 timeframe, and thereby consider finalizing these useful life mileages in this rule. We did not evaluate alternative useful life mileages for HD SI refueling standards. As noted in Section IV.A.3.iii, we would consider transitional useful life mileages for our refueling standards in the early years of the program or longer useful life mileages that align with those for the final Spark-ignition HDE class if we receive comment and data supporting alignment.

Our analyses of the emission impacts of the Alternative standards and Alternative useful life mileage values are presented in Section VI. We do not present an analysis of the costs of the Alternative since we currently do not have information to conclude that the Alternative standards are feasible in the MY 2027 timeframe with the emission control technologies we have evaluated to date. We are also considering other approaches that build on the relationship between useful life and emissions warranty periods as described in Section IV.B.1.

5. Summary of the Requests for Comment on the Useful Life Proposal

We request comment on our proposed useful life values, including the appropriateness of the data on which we base our proposals, or other bases identified in this section or by the commenters. Specifically, we request comment on our approaches to base useful life mileages for CI engines on data on average mileage to first out-of-frame rebuild for proposed Option 1 and average mileage to first in-frame rebuild for proposed Option 2. We also request comment on whether to finalize a consistent fraction of the estimated rebuild mileage across the three CI service classes. For SI engines, we request comment on our proposed Option 1 approach to update the MY 2031 useful life mileage based on the advertised service life of a certified SI engine in the market today, which is consistent with SI engine mileage from recent CARB study, or the proposed Option 2 approach to update the criteria pollutant useful life to be closer to the useful life mileage that applies for GHG pollutants. As noted in this section and discussed in Section III, proposed Options 1 and 2 reflect the general ranges of mileages we are currently considering for each engine class, but we request comment on a different set of mileages within those ranges that may be appropriate. Commenters, especially if suggesting different useful life mileages than EPA's proposed values, are encouraged to support their comments by addressing feasibility and cost for their recommended mileage values.

We request comment on our proposal to increase the useful life years and to update Heavy HDE useful life hours-based values proportional to the increased mileages for proposed Option 1. Commenters supporting useful life hours for Heavy HDE are encouraged to address whether EPA should apply a useful life hours criterion to other engine service classes and if a 20 mile per hour average speed is appropriate to represent “low speed” applications for each engine class. As noted in this section, proposed Option 1 is largely aligned with useful life periods adopted in the CARB HD Omnibus regulation. We request comment our proposal, including whether it is appropriate to fully harmonize the federal and CARB regulatory useful life periods in light of the authority and requirements of section 202, and any concerns if EPA were to finalize aspects of useful life that are or are not aligned with CARB for a given engine class or range of model years.

B. Ensuring Long-Term In-Use Emissions Performance

In the ANPR, we introduced several ideas for an enhanced, comprehensive strategy to ensure in-use emissions performance over more of an engine's operational life, based on five areas:

• Warranties that cover an appropriate fraction of engine operational life.
• Improved, more tamper-resistant electronic controls.
• Serviceability improvements for vehicles and engines.
• Education and potential incentives.
• Engine rebuilding practices that ensure emission controls are functional.
• This section discusses proposed provisions for emissions warranty, ECM security, and serviceability. Taken together, they are intended to increase the likelihood that engine emission controls will be maintained properly through more of the service life of heavy-duty engines and vehicles, including beyond useful life. Our proposal also expands on this suite of measures to include updated maintenance provisions, which are described in Section IV.B.5. We are not including specific proposals related to education and incentives, but request comment on options we could consider in the future. As noted in Section IV.B.4, we are also not proposing new or modified rebuilding provisions in this rule. However, we intend to continue to monitor rebuilding practices and may update our rebuilding regulatory provisions in a future rulemaking.

1. Emission-Related Warranty Periods

EPA is proposing to lengthen the regulatory emission-related warranty periods for all primary intended service classes to cover a larger portion of the operational lives of new heavy-duty engines. In this section we summarize the history of emissions warranty, introduce our principles for lengthening the warranty periods, and present our proposed values and alternatives considered.

i. EPA Regulatory Emission Warranty Background

The regulatory emission warranty period is the period over which CAA section 207 requires an engine manufacturer to warrant to a purchaser that the engine is designed, built, and equipped so as to conform with applicable regulations under CAA section 202 and is free from defects in materials or workmanship which would cause the engine not to conform with applicable regulations for the warranty period. If an emission-related component fails during the regulatory emission warranty period, the manufacturer is required to pay for the cost of repair or replacement. A manufacturer's general emissions warranty responsibilities are currently set out in 40 CFR 1068.115. Note that while an emission warranty provides protection to the owner against emission-related repair costs during the warranty period, the owner is responsible for properly maintaining the engine (40 CFR 1068.110(e)), and the manufacturer may deny warranty claims for failures that have been caused by the owner's or operator's improper maintenance or use (40 CFR 1068.115(a)).

Regulatory warranty provisions were first included in the 1970 amendments to the Clean Air Act, as a new section 207(a) (“the manufacturer of each new motor vehicle and new motor vehicle engine shall warrant to the ultimate purchaser and each subsequent purchaser that such vehicle or engine is (1) designed, built, and equipped so as to conform at the time of sale with applicable regulations under section 202, and (2) free from defects in materials and workmanship which cause such vehicle or engine to fail to conform with applicable regulations for its useful life . . .”). Those amendments also instructed the Administrator in section 202(b) to “prescribe regulations which shall require manufacturers to warrant the emission control device or system of each new motor vehicle or new motor vehicle engine to which a regulation under section 202 applies . . .” emphasis added). The 1977 CAA amendments modified the section 207(b) requirements, specifying that “for the period after twenty-four months or twenty-four thousand miles (whichever first occurs) the term 'emission control device or system' means a catalytic converter, thermal reactor, or other component installed on or in a vehicle for the sole or primary purpose of reducing vehicle emissions.” EPA's first heavy-duty truck regulations, promulgated in 1983, set a specific warranty period of 5 years or 50,000 miles, whichever occurred first, for light-duty trucks, gasoline heavy-duty engines, and light heavy-duty diesel engines, and 5 years or 100,000 miles, whichever occurred first, for all other heavy-duty diesel engines. These emission warranty periods were carried over in each subsequent revision of the emission control program (see 40 CFR 86.084-2, 86.085-2, 86.90-2, 86.94-2, 86.096-2, 86.004-2) and persist to this day, even as the engine useful life periods were increased. Today, there is a considerable difference between useful life and emission warranty periods, as illustrated in Table IV-7. The proposed changes to the useful life periods described in Section IV.A would increase this difference in the absence of an accompanying change to emissions warranty periods.

Today, the warranty mileage for Spark-ignition HDE, Light HDE, and Medium HDE covers about half of the corresponding useful life for those engines; the warranty mileage for Heavy HDE covers about a quarter of useful life. The proposal to lengthen engine useful life means that the warranty period would cover a smaller portion of useful life unless the warranty period is also increased. In the following section, we describe ways in which emission warranty periods can impact long-term emission performance, which we believe justifies proposing emissions warranties that cover more of the operational life of the engine.

ii. Lengthening the Regulatory Emission Warranty Period To Improve Long-Term Emission Performance

As illustrated in Table IV-7, EPA's current emissions-related warranty periods range from 22 percent to 54 percent of regulatory useful life; the warranty periods have not changed since 1983 even as the useful life periods were lengthened. As EPA is proposing to lengthen the useful life periods in this rulemaking, we are also proposing to lengthen the emission warranty periods and increase the portion of useful life miles covered under warranty. These proposed revised warranty periods are expected to result in better engine maintenance and less tampering, helping to maintain the benefits of the emission controls. In addition, longer regulatory warranty periods may lead engine manufacturers to simplify repair processes and make them more aware of system defects that need to be tracked and reported to EPA.

Longer regulatory warranty periods that are more consistent with EPA's useful life periods are expected to lead owners to better maintain their engines and vehicles over a longer period of time so as to not void their emission warranty coverage. This is because existing warranty provisions specify that owners are responsible for properly maintaining their engines (40 CFR 1068.110(e)), and manufacturers may deny warranty claims for failures that have been caused by the owner's or operator's improper maintenance or use (40 CFR 1068.115(a)). A longer warranty period is expected to lead to better engine emission performance overall due to less mal-maintenance (see Chapter 5 of the draft RIA for a discussion of mal-maintenance effects in our emission inventory estimates). Similarly, longer regulatory emission warranty periods are expected to reduce the likelihood of tampering, which would also result in better engine emission performance (see Chapter 5 of the draft RIA for a discussion of tampering effects in our emission inventory estimates). Since emission-related repairs would be covered for a longer period of time, the owner will be more likely to have systems repaired and, consequently, may be less likely to tamper to avoid the cost of a repair that is no longer covered by a warranty. Owners may also be less likely to install defeat devices that are marketed to boost engine performance since installing such a device would void the engine warranty.

Emission-related repair processes may get more attention from manufacturers if they are responsible for repairs over a longer period of time. As manufacturers try to remain competitive, longer emission warranty periods may lead manufacturers to simplify repair processes and provide better training to technicians in an effort to reduce their warranty repair costs. Simplifying repair processes could include modifying emission control components in terms of how systems are serviced and how components are replaced. The current, relatively short warranty period provides little incentive for manufacturers to specify repairs be made at the lowest possible level of complexity, since the owner pays for the repairs after the warranty period ends. One way to reduce warranty repair costs may be to design modular sub-assemblies that could be replaced individually, resulting in a quicker, less expensive repair. For example, if a DEF level sensor fails, repair practices may call for the DEF sensor assembly to be replaced in its entirety (including level sensor, quality sensor, lines, and even heaters) instead of only the faulty part. Improved technician training may also reduce warranty repair costs by improving identification and diagnosing component failures more quickly and accurately, thus avoiding repeated failures or misdiagnoses of failures and higher costs from repeat repair events at service facilities. These improvements may also encourage owners to have repairs made because down time is reduced.

Finally, longer regulatory emission warranty periods would increase the period over which the engine manufacturer would be made aware of emission-related defects. Manufacturers are currently required to track and report defects to the Agency under the defect reporting provisions of 40 CFR part 1068. Under 40 CFR 1068.501(b), manufacturers investigate possible defects whenever a warranty claim is submitted for a component. Therefore, manufacturers can easily monitor defect information from dealers and repair shops who are performing those warranty repair services, but after the warranty period ends, the manufacturer would not necessarily know about these events, since repair facilities are less likely to be in contact with the manufacturers and they are less likely to use OEM parts. A longer warranty period would allow manufacturers to have access to better defect information over a period of time more consistent with engine useful life.

The impact of a longer emissions warranty period may be slightly different for SI engines. Spark-ignition engine systems rely on mature technologies, including evaporative emission systems and three-way catalyst-based emission controls, that have been consistently reliable for light-duty and heavy-duty vehicle owners. We expect lengthened emission warranty periods to help enhance long-term in-use emissions performance of SI engines over time by reducing mal-maintenance and tampering. Similar to CI engine owners, we believe a longer warranty period would encourage owners of vehicles powered by SI engines to follow manufacturer-prescribed maintenance procedures for a longer period of time, as failure to do so would void the warranty. From a tampering perspective, SI engine owners may not be motivated to tamper with their catalyst systems to avoid repairs, but they may be less inclined to purchase defeat devices intended to disable emission controls to boost the performance of SI engines since installing such a device would void the engine warranty.

EPA seeks comment on all aspects of our proposal to lengthen emissions warranty periods for all primary intended service classes. We encourage stakeholders to submit any available data on emission control system repairs during and after heavy-duty engine emission warranty periods, including frequency of incidents, costs of repairs, and associated downtime.

iii. CARB's Recent Heavy-Duty Engine Emissions Warranty Updates

CARB recently finalized two regulatory programs to update emissions warranty periods for heavy-duty engines as summarized in this section. We considered the warranty updates adopted by CARB when developing the proposed warranty periods for this rulemaking.

CARB's “Step 1” warranty program for heavy-duty engines sold in California was finalized in 2019 and applied to MY 2022 heavy-duty diesel engines. CARB increased the warranty mileage values for heavy-duty diesel engines, but did not update the years-based warranty periods during the Step 1 update. The Step 1 program also formally linked warranty requirements to the HD OBD system by specifying that failures that cause the vehicle's OBD MIL to illuminate are considered warrantable conditions. CARB justified this linkage as helping to ensure that repairs of malfunctioning emission-related parts would be performed in a timelier manner during the lengthened warranty periods.

CARB included a second step of warranty updates in their HD Omnibus rulemaking that was approved by the Board in 2020. In the Omnibus regulation, CARB lengthened the warranty periods for MY 2027 through MY 2030 and further lengthened the warranty periods for MY 2031 and later heavy-duty diesel engines. The Omnibus regulation also lengthened warranty periods for heavy-duty Otto cycle engines, and similarly linked HD OBD MIL triggers to warrantable conditions, for the same model years. The Omnibus also requires hybrid configurations to meet the same warranty periods as the diesel or Otto cycle engine service class to which they are certified. In addition, the Omnibus included warranty periods for BEVs and FCEVs of 3 years or 50,000 miles. The warranty periods adopted in the Omnibus included updated years- and hours-based warranty periods. The hours-based values were generally based on a 20 miles per hour vehicle speed and the warranty mileage for each engine class. Table IV-8 summarizes the emissions warranty periods from CARB's recent updates.

CARB's warranty updates were partially motivated by evidence that emission-related component failures occur after the end of the current emission warranty periods, when manufacturers are no longer responsible for repair or replacement costs under the warranty provisions, but before the end of the engine's regulatory useful life, through which time engines are certified by the manufacturer to meet the emission standards. According to the Updated Informative Digest prepared for CARB's Amendments to California Emission Control System Warranty Regulations and Maintenance Provisions, “CARB's test programs have identified numerous heavy-duty vehicles with mileages within their applicable regulatory useful life periods, but beyond their warranty period, that have NO_X emission levels significantly above their applicable certification standards.” These incidents may not be frequent enough to trigger an emission recall under California's program, but CARB noted concern about engine-specific emission equipment failures not covered by warranty. In addition, a survey of owners and repair shops performed for CARB with respect to downtime for repairs found that over half of the owners surveyed experienced downtime to address repairs, and more than 60 percent of those repairs were not covered by emission warranties.

The market for extended warranties suggests that some truck purchasers are concerned enough about out-of-warranty repairs to be willing to purchase additional warranty coverage, either directly from the manufacturers or from independent third parties. According to a survey conducted on behalf of CARB in support of their heavy-duty warranty program, approximately 40 percent of all new heavy-duty vehicle buyers “purchase or receive” an extended warranty under which the coverage is extended to 417,000 miles on average. This survey data correlates with information provided to CARB by the Truck and Engine Manufacturers Association, which indicated that 50 percent of new heavy-duty Class 8 vehicles are sold with a 500,000 mile extended warranty.

iv. Proposed Emissions Warranty Provisions

This section describes the proposed regulatory emissions warranty provisions, including the lengthened warranty periods we are proposing, by engine category and the components covered. Our proposed warranty provisions are in a new 40 CFR 1036.120. We request comment on the proposed warranty mileage values, as well as the corresponding age-based criteria. Commenters also are encouraged to address whether warranty periods should be a consistent fraction of the final useful life periods and whether we should align with CARB's Omnibus program when considering warranty periods for the final rule.

a. Proposed Warranty Periods by Primary Intended Service Class

We are proposing to update our emissions warranty periods for emission-related components designed to reduce criteria pollutant emissions, beginning with model year 2027 and later heavy-duty engines. Following our approach for the proposed useful life periods, we are proposing two options (proposed Options 1 and 2) and our proposed warranty periods vary by primary intended service class to reflect the difference in average operational life of each class.

When a manufacturer's certified configuration includes hybrid system components ( e.g., batteries, electric motors, and inverters), those components are considered emission-related components, which would be covered under the proposed warranty requirements in new 40 CFR 1036.120. Similar to the proposed approach for useful life in Section IV.A, we are proposing that a manufacturer certifying a hybrid engine or hybrid powertrain would declare a primary intended service class for the engine family and apply the corresponding warranty periods in the proposed 40 CFR 1036.120 when certifying the engine configuration.

Also similar to our proposal for useful life, our proposed approach to clarify that hybrid components are part of the broader engine configuration provides truck owners and operators with consistent warranty coverage based on the intended vehicle application.

Currently, emission warranties for most HD engine classes (Spark-ignition HDE, Light HDE, and Medium HDE) cover about half of the respective useful life mileages. As mentioned in Section IV.B.1.ii, we believe that fewer incidents of mal-maintenance and tampering occur during the warranty period, and thus fewer would occur overall if the warranty period is lengthened. Consistent with our current requirements, we believe it is appropriate to propose to lengthen the warranty mileage to continue to cover at least half of the useful life mileage for all engine classes.

More specifically, we are proposing two options that generally represent the range of revised emission warranty periods we are considering adopting in the final rule. Proposed Option 1 includes warranty periods that are aligned with the MY 2027 and MY 2031 periods adopted by CARB, which are close to 80 percent of useful life. At this time, we assume most manufacturers would continue to certify 50-state compliant engines in MY 2027 and later, and it would simplify the certification process if there is consistency between CARB and federal requirements. The warranty periods of proposed Option 2 would apply in a single step beginning in model year 2027, and would match CARB's Step 1 warranty periods that will already be in effect beginning in model year 2022 for engines sold in California. The proposed Option 2 mileages cover 40 to 55 percent of the proposed Option 1 MY 2031 useful life mileages and represent an appropriate lower end of the range of the revised regulatory emission warranty periods we are considering. Our proposed emissions warranty periods for heavy-duty engines are presented in Table IV-9. We estimated the emissions impacts of the proposed warranty periods in our inventory analysis, which is summarized in Section VI and discussed in detail in Chapter 5 of our draft RIA. In Section V, we estimated indirect and operating costs associated with the proposed warranty periods.

While we believe a majority of engines would reach the warranty mileage in a reasonable amount of time, some applications may have very low annual mileage due to infrequent use or low speed operation; these engines may not reach the warranty mileage for many years. To ensure manufacturers are not indefinitely responsible for components covered under emissions warranty in these situations, we are proposing revised years-based warranty periods and new hours-based warranty periods for proposed Option 1 and new hours-based warranty periods for proposed Option 2. Consistent with current warranty provisions, the warranty period would be whichever warranty value ( i.e., mileage, hours, or years) occurs first.

For the years-based period, which would likely be reached first by engines with lower annual mileage due to infrequent use, proposed Option 1 would increase the current period from 5 years to 7 years for MY 2027 through 2030, and to 10 years starting with MY 2031. We are also proposing to add an hours-based warranty period to both proposed options, as shown in Table IV-9, to cover engines that operate at low speed and/or are frequently in idle mode. In contrast to infrequent use, low speed and idle operation can strain emission control components and we believe it is appropriate to factor that gradually-accumulated work into a manufacturer's warranty obligations. We are proposing warranty hours for all primary intended service classes based on a 20 mile per hour average vehicle speed threshold to convert from the proposed mileage values. We note that applying a consistent 20 miles per hour conversion factor to the proposed mileage periods would result in a variable number of years of warranty coverage across classes and, in some cases, fewer years than the years-based period for a given model year. We request comment on applying a different conversion speed for all classes or a unique speed to each engine class to calculate the hours-based periods.

Consistent with existing regulations, our proposed warranty provisions in new 40 CFR 1036.120(c) identify the components covered by emission warranty as the general emission-related components listed in 40 CFR 1068, appendix A, and any other components a manufacturer may develop to control emissions. The emission-related components listed in Appendix A are broad categories of components and systems that affect emissions. We request comment on the completeness of this list and whether we should consider adding other or more specific components or systems. We also request comment on whether it is appropriate to expand the list of components covered by emission warranty to include any component whose failure causes the vehicle's OBD MIL to illuminate, as adopted by CARB. While we agree that an OBD MIL could be used by an owner or technician to identify an underperforming or failed emission-related component that should be replaced under warranty, we currently have concerns that not all OBD MILs are tied directly to an emission-related component. If we were to finalize a link between warranty and OBD MILs, we expect the cost of expanding the list of warrantable components to include all components that may trigger an OBD MIL, regardless of their direct impact on emissions, would be unreasonable.

b. Proposed Warranty for Heavy-Duty Electric Vehicles

Similar to the proposed approach for BEV and FCEV useful life periods, described in IV.A, we are proposing in 40 CFR 1037.120(b)(2) that BEV and FCEV manufacturers apply the warranty periods corresponding to an engine-based primary intended service class, as specified in the proposed 40 CFR 1037.120(b). The proposed 40 CFR 1037.120(b)(2) specifies that prior to MY 2027 manufacturers choosing to generate NO_X emission credits in MYs 2024 through 2026 would apply the warranty periods in the current 40 CFR 86.001-2; starting in MY 2027 manufacturers would apply the warranty periods specified in the proposed 40 CFR 1036.104. Manufacturers choosing not to generate NO_X emission credits with their BEVs or FCEVs could alternatively choose in MY 2027 or later to certify to the existing emission warranty requirements for GHGs, as specified in the current 40 CFR 1037.120(b)(1). As specified in the existing 40 CFR 1037.120(e), all manufacturers would continue to describe in their owners' manual the warranty provisions that apply to the vehicle.

As discussed in Section IV.A, data from BEV transit buses and DOE research and development work on FCEVs suggest that BEV and FCEV technologies will be capable of operating over mileages or time periods similar to CI engines in the 2027 and beyond timeframe; thus, we believe it is appropriate for the same criteria pollutant warranty requirements to apply to BEV and FCEV technologies as those specified for CI engines for those manufacturers who choose to generate NO_X emission credits.

We further recognize that repeated repair or maintenance issues with a BEV or FCEV could increase vehicle operating costs and lead owners to purchase a vehicle powered by a CI or SI engine instead, which would result in higher emissions than a zero-emission tailpipe battery or fuel cell electric vehicle. Our proposed BEV and FCEV warranty requirements for manufacturers who choose to generate NO_X emission credits from BEVs or FCEVs are expected to decrease those operating costs in two ways. First, by encouraging owners to conduct vehicle maintenance that ensures continued warranty coverage and maintains the benefits of the zero-tailpipe emission performance. Second, by encouraging manufacturers to simplify repair processes and provide better training to technicians in an effort to reduce their warranty repair costs.

As specified in the proposed 40 CFR 1037.120(c), we propose to clarify that batteries and fuel cells in BEVs and FCEVs, respectively, are considered covered components and would be subject to the proposed warranty requirements in 40 CFR 1037.120(b)(2) for manufacturers choosing to generate NO_X emission credits. Our proposed approach for component coverage reflects that defects or failures of batteries or fuel cells could render the vehicle inoperable, and thus the vehicle would cease to provide zero tailpipe emission performance over the full useful life period despite having generated emission credits for the full useful life period. We note that our proposed approach is less comprehensive than the CARB Zero Emission Powertrain (“ZEP”) Certification approach, which defines “warranted part” as “any powertrain component” in the case of zero-emission powertrains. At the end of this subsection we request comment on our proposed approach for component coverage relative to the CARB ZEP Certification approach.

In developing our proposal for the duration of the warranty period for BEVs and FCEVs, we considered two other options: (1) Align with CARB Omnibus emission warranty requirements for BEVs and FCEVs of 3 years or 50,000 miles, or (2) align criteria pollutant warranty periods with the periods specified for GHG emissions in the current 40 CFR 1037.120 for all manufacturers. The CARB Omnibus warranty requirements for BEVs and FCEVs match what manufacturers are already required to offer if they participate in the California Heavy-duty Vehicle Incentive Program (HVIP), and are less than industry standards for warranty periods based on information submitted to CARB through the certification process. The second option we considered, aligning criteria pollutant and GHG warranty periods for BEVs and FCEVs would be a simplistic approach, but would not recognize the use of these technologies to generate NO_X emission credits; under the proposed ABT program, we would allow these NO_X emission credits to be used to produce higher-emitting engines with longer warranty period requirements. As such we are proposing that only manufacturers who choose not to generate NO_X emission credits with BEVs or FCEVs could choose to certify to criteria pollutant warranty requirements equivalent to the existing GHG emission warranty requirements.

We request comment on our proposed approach for BEV and FCEV warranty requirements to match those of the engine-based primary intended service class for manufacturers who choose to generate NO_X emission credits from BEVs or FCEVs. Commenters are encouraged to provide information and data on whether such requirements would help to ensure the zero-emission tailpipe performance of these technologies, or if they would hinder the integration of these technologies into the heavy-duty vehicle market. If commenters suggest that we should finalize another alternative to our proposed approach, then we request information and data supporting their views on how such an alternative would support the environmental benefits of zero-emission tailpipe technologies. We further request comment on our proposed approach that batteries and fuel cells in BEVs and FCEVs, respectively, are covered under warranty for manufacturers choosing to generate NO_X emission credits. If commenters suggest that we include additional components in the final rule, such as the CARB ZEP Certification approach, we request that commenters provide a list of which specific components should be covered ( e.g., electric motor, axles), along with a rationale for why those components should be covered under emission warranty.

c. Proposed Warranty for Incomplete Vehicle Refueling Emission Standards

As noted in Section III.E, proposed Options 1 and 2 include refueling emission standards for Spark-ignition HDE that are certified as incomplete vehicles above 14,000 lb GVWR. Our proposed refueling standards are equivalent to the refueling standards that are in effect for light- and heavy-duty complete Spark-ignition HDVs. We project manufacturers would adapt the existing onboard refueling vapor recovery (ORVR) systems from those complete vehicle systems to meet our proposed refueling standards.

As noted in Section III.E, we are not reopening or proposing to change evaporative emission requirements that currently apply for all SI engines or refueling emission standards that currently apply for complete vehicles. Because the onboard refueling vapor recovery systems necessary to meet the proposed refueling standards are expected to build on existing evaporative systems, proposed Options 1 and 2 would require that Spark-ignition HDE manufacturers provide a warranty for the ORVR systems of incomplete vehicles above 14,000 lb GVWR for the same warranty periods that currently apply for evaporative emission control components on these vehicles. Our proposal to apply the existing warranty periods for evaporative emission control systems to the ORVR systems is similar to our approach to the regulatory useful life periods associated with our proposed refueling standards discussed in Section IV.A.

v. Additional Considerations for Components Covered and Warranty Claims

Consistent with existing regulations, our proposed warranty provisions in new 40 CFR 1036.120(c) identify the components covered by emission warranty as the general emission-related components listed in 40 CFR 1068, appendix A, and any other components a manufacturer may develop to control emissions. The emission-related components listed in appendix A are broad categories of components and systems that affect emissions. We request comment on the completeness of this list and whether we should consider adding other systems or more specific components of systems.

As mentioned in Section IV.B.1.iii, CARB recently expanded their list of components covered by emission warranty to include any component whose failure causes the vehicle's OBD MIL to illuminate to ensure malfunctioning components were repaired in a timely manner. We believe the proposed lengthened warranty periods would effectively encourage prompt maintenance without the need to expand the list of components covered beyond those specifically identified as emission-related components. We are also including several other proposed updates to improve access to valuable maintenance information for certain emission-related components. We are proposing to require manufacturers to update their owner's manuals to improve serviceability (Section IV.B.3) and to expand the list of OBD parameters available to the public (Section IV.C).

As specified in the current 40 CFR 1068.115 and referenced in proposed 40 CFR 1036.120(d), manufacturers may deny warranty claims if the engine was improperly maintained or used. In proposed 40 CFR 1036.125(h)(2), manufacturers would describe the documentation they require for owners to demonstrate their engines are properly maintained. ANPR commenters suggest that DEF quality sensor data alone is an incomplete indicator of an owner's commitment to maintaining high-quality DEF. EPA received comments describing incidents where DEF quality faults were triggered repeatedly despite flushing the system and filling the tank with new DEF, suggesting a fault with a system sensor. A recent online discussion indicates that some OEMs may be denying warranty claims on the basis of using poor quality DEF. While this may be justified for repeated DEF quality faults or extremely low urea concentrations ( e.g., using water), DEF quality sensor readings may also indicate only slightly abnormal urea concentrations due to unintentionally long storage periods or unpredicted improper storage temperatures. In either case, we expect a DEF quality-triggered engine derate would induce a user to address the DEF quality issue before it would cause a problem downstream.

We note that current 40 CFR 1068.115 allows manufacturers to deny a warranty claim only if they show that a component failure was due to improper maintenance or use by the owner or operator, by accidents for which the manufacturer has no responsibility, or by acts of God subject to certain limitations. For example, 40 CFR 1068.115(b)(3) does not allow a manufacturer to deny a warranty claim based on action or inaction by the operator unrelated to the warranty claim. In proposed 40 CFR 1036.120(d), we propose to further clarify that, as described in 40 CFR 1068.115, for highway heavy-duty engines a manufacturer may deny warranty claims if the operator caused the problem through improper maintenance or use. In other words, a manufacturer must use more than just the presence of a system fault before denying a warranty claim for improper maintenance and would have to show that a component failure was directly connected to that fault. We request comment on the availability of high-quality DEF and whether EPA should explicitly state that manufacturers cannot deny warranty claims based on the use of commonly available DEF, as is currently specified for fuel in 40 CFR 1068.115(b)(6). Commenters are encouraged to suggest if a commonly available DEF provision should be limited to heavy-duty highway engines in 40 CFR 1036.120 or if it should be broadly applied to all sectors covered under part 1068.

vi. Analysis of Proposed Emission Warranty Periods and Alternatives

Consistent with our useful life discussion in Section IV.A.4, we considered an alternative set of warranty periods (the Alternative) that would apply as a single step beginning in model year 2027. The warranty mileages for the Alternative are longer than the proposed Option 1 MY 2031 useful life mileages. The Alternative mileages align with the warranty mileages presented in CARB's September 2019 Public Workshop for their Heavy-Duty Low NO_X program and cover up to 94 percent of the useful life mileages considered for the Alternative. The warranty mileages of the Alternative would place an even greater emphasis on the importance of holding manufacturers responsible for emission control defects for a period of time that aligns more closely with the operational life of the engine. However, we believe it would be inappropriate to consider warranty mileages equal to or beyond the proposed Option 1 MY 2031 useful life mileages, which are the maximum useful life mileages we consider to be feasible given the level of emission standards evaluated in this proposal based on available data.

The Alternative warranty mileages are equivalent to or longer than the useful life mileages included in the proposed Options 1 and 2. Since we do not believe that the emission warranty period should be equal to or greater than the useful life period, we focus on the warranty values of proposed Options 1 and 2 and the range in between them for this proposal. We expect that we would need additional data before we could project that the standards and useful life values of the Alternative are feasible for the MY 2027 timeframe in order to consider adopting them, or the Alternative warranty mileages, in the final rule.

We estimated the emissions impacts of the Alternative warranty periods in our inventory analysis, which is summarized in Section VI and discussed in detail in Chapter 5 of our draft RIA. We do not present an analysis of the costs of the Alternative, since those warranty periods are out of the range of mileages we are currently considering without additional information to indicate that the standards and useful life values of the Alternative are feasible in the MY 2027 timeframe.

vii. Other Approaches To Ensure Long-Term In-Use Emission Performance

Under our current and proposed warranty provisions, parts and labor for emission-related components are equally and fully covered over the entirety of the warranty period. A graduated warranty coverage approach, which was introduced as a topic in the ANPR to this rule and is described in more detail below, may provide a similar assurance of long-term emission performance with a smaller impact on the purchase price.

Manufacturers are responsible for repairing or replacing emission-related components that are found to be defective within the specified warranty period. Manufacturers include warranty repairs in the price of an engine or vehicle, and the Agency considers the warranty cost implications of all our emission control rules. In Section V, we provide the cost impacts of the proposed warranty periods. The impact that a longer warranty would have on the purchase price of an individual engine will vary by factors such as a manufacturer's estimate of the risk for an engine, their presumed competition in the market, and their relationship with the purchaser.

In the current market, purchasers desiring greater warranty protection can buy extended warranties, either from the engine manufacturers or third-party companies. The experience with extended warranties reveals information about the range of owner preferences with respect to bearing the costs of out-of-warranty repairs. Some of the estimated 40 percent of purchasers obtaining extended warranties may be large companies that purchase extended warranty coverage because they have comprehensive in-house service facilities and a business relationship with engine manufacturers that allows them to perform warranty repairs in-house. Other owners may be reliant on the engine manufacturer for warranty repairs but prefer to purchase extended warranties for insurance against the cost of out-of-warranty repairs, in essence paying for those repairs up-front. Of the 60 percent of purchasers that decline to purchase extended warranties, some companies may reduce the risk of out-of-warranty repair costs by selling their vehicles near the point when the warranty period ends. Others may prefer to pay for out-of-warranty repairs when and if they occur. Still others may choose to not make out-of-warranty repairs at all. It is clear that lengthening the warranty period would remove some of a purchaser's flexibility to address out-of-warranty repair costs. We request comment on the extent to which emissions warranty period is an important aspect of purchasers' business decisions, and the specific impacts purchasers anticipate for the range of emissions warranty periods we are considering in this rule. For instance, we are interested in how a longer regulatory emissions warranty may impact the timing of an engine or truck purchase, how long an engine or vehicle is kept, and/or how well an engine is maintained.

In the ANPR, we described two different potential approaches to graduated warranties. Under one approach, there could be longer, prorated warranties that provide different levels of warranty coverage based on a vehicle's age or mileage. Alternatively, the warranty could be limited to include only certain parts during specified warranty periods, and/or exclude labor for some, or even all, of the duration of coverage. We received feedback from several stakeholders in response to the ANPR. Allison Transmission supported EPA considering prorated parts and labor as an approach to lengthening warranty periods. Volvo suggested that applying the longer warranty periods to only critical components could be a way to reduce manufacturer costs. NADA recommended that longer warranty periods be proposed in a manner that varies by class of component or system and include the approaches EPA presented in the ANPR such as limited component and/or prorated warranties.

We are not proposing and did not analyze a graduated warranty approach for this proposal. However, we may consider a graduated warranty as a viable alternative to our proposed warranty periods if we receive additional information that would support such an approach. A graduated warranty approach could extend beyond our proposed warranty periods in mileage, hours, and years, to cover more of the operational life of the engine, but it could be based on different phases of varying coverage. These could include, for example:

• Phase 1: Full parts and labor coverage for all emission-related components,
• Phase 2: Parts and labor coverage for limited emission-related components, and
• Phase 3: Parts-only coverage for limited emission-related components.

We request comment on whether EPA should adopt a phased approach for a longer emission warranty period. Supporters of such an approach should comment on the number of phases, the length of each phase, and the components to include in the set of limited emission-related components under such an approach. With respect to Phase 1, which would be similar to a traditional warranty with full parts and labor coverage, EPA may consider the warranty mileages in proposed Option 2 as the minimum lower bound. For the other phases, commenters are encouraged to include data to support their suggested mileage, hours, and years of coverage. When considering the set of limited parts to be covered in the other phase(s), EPA may consider including components that are relatively high-cost components, or components that are labor-intensive (and thus expensive) to replace. We request data to support the set of limited emission-related components that should be included in the other phase(s), including failure rates, component costs, and labor costs to replace specific components. We note that our proposed maintenance provisions in 40 CFR 1036.125 include two categories of components we could consider as the set of limited emission-related components covered in the graduated warranty approach. As described in Section IV.B.5, these two categories of components include a proposed list of specific components with minimum maintenance intervals, and criteria to identify components that can only be replaced as part of scheduled maintenance if the manufacturer covers the cost.

Finally, we request comment on whether a graduated warranty approach would achieve the goals set out in Section IV.B.1.ii: Providing an extended period of protection for purchasers, encouraging proper maintenance, discouraging tampering, and incentivizing manufacturers to design emission control components that are less costly to repair.

2. Electronic Control Module Security

CAA section 203(a)(3)(B) and 40 CFR 1068.101(b)(2) prohibit selling, offering to sell, or installing any part or component whose principal effect is to bypass, defeat, or render inoperative a motor vehicle emission control device or element of design ( i.e., a “defeat device”), where the person knows or should know that the part is being offered for sale, installed for such use or put to such use. Once installed, defeat devices can result in significant tailpipe emissions increases, and with the long service life of heavy-duty vehicles, would produce a disproportionate amount of lifetime emissions, compared to a vehicle with properly functioning emission controls. One of the key enablers of defeat devices with modern engines is the unauthorized modification, or tampering, with certified calibration parameters and/or software within the electronic control module (“ECM”). Tampering with the ECM can introduce a different calibration that allows the engine to produce power at higher emission rates, or it can bypass or disable inducement algorithms intended to ensure proper functioning of SCR systems. The EPA Office of Enforcement and Compliance Assurance (OECA) has found extensive evidence of tampering with the emission control systems on heavy-duty engines and vehicles nationwide, although EPA lacks robust data on the exact rate of tampering. Recently, OECA announced a new National Compliance Initiative (“NCI”) to address the manufacture, sale, and installation of defeat devices on vehicles and engines through civil enforcement.

EPA has for decades had regulations to address the “physically adjustable parameters” on heavy-duty highway engines that can alter emissions performance. These regulations require the manufacturer, subject to review by EPA, to identify the appropriate range of adjustment on the operating parameters or physical settings on an engine that could potentially increase emissions and the adequacy of limits, stops, seals, or other mechanical means of limiting or prohibiting adjustment outside of these appropriate ranges. Parameters such as injection timing on a diesel engine were once physically adjustable with common tools and clearly an adjustable parameter. With a modern ECM, many of these parameters are now electronically adjustable through changes to software and calibration settings. As discussed in Section XII.A.2, we are proposing to revise our regulations by adding 40 CFR 1068.50 to specifically address electronically adjustable parameters and require that manufacturers attest that they are using sufficient measures to secure the ECM, thereby limiting adjustment or alteration beyond those used in the certified configuration.

ECM tampering is often designed to avoid detection, where the software, controls, and onboard diagnostics are intentionally manipulated so commonly available scan tools cannot detect the presence of a defeat device. This complicates the efforts of state inspection and maintenance programs to identify and address tampered vehicles. ECM tampering is also a concern for manufacturers, because changes to the engine controls can adversely impact the durability of the engine and lead to premature failure. If ECM tampering remains undetected and a failure occurs within the warranty period, the manufacturer would be responsible for the repair costs. Manufacturers have been implementing measures to prevent tampering with software in the engine's ECM, but manufacturers of defeat devices continue to find ways to work around these security measures. Unauthorized access to the ECM and other control modules on a vehicle is also a public safety concern, as malicious tampering could affect the operation of the advanced braking, stability, and cruise control systems found on modern heavy-duty vehicles.

To address the safety, financial liability, operational, and privacy concerns that can result from tampering, manufacturers, industry organizations, and regulators have been working to develop standards and design principles that would improve vehicle cybersecurity, including ECMs. Three such efforts where cybersecurity guidelines and procedures are either under development or already in publication are ISO/SAE J21434, UNECE WP29 Cybersecurity Regulation,

and SAE J3061.^{508 509} Manufacturers may choose to utilize different mixes of technical standards or principles that these organizations recommend. A one-size-fits-all approach with detailed requirements for ECM security for all engines would be neither practical nor prudent. Manufacturers need the flexibility to quickly implement measures to address new or emerging threats and vulnerabilities. Considering this need for flexibility and noting that the security principles in these efforts are constantly evolving as new threats are identified, we are not proposing to adopt any of these specific guidelines as requirements for manufacturers.

In 40 CFR 1036.205(s), we propose that manufacturers describe all adjustable parameters in their application for certification, which would include electronically controlled parameters. Electronically controlled parameters may be considered practically adjustable as described in proposed 40 CFR 1068.50(d)(2). This would include user-selectable operating modes and modifications that owners can make with available tools. We are proposing that manufacturers describe their approach to limiting access to electronic controls in the certification application. We retain the right to evaluate a manufacturer's determination in their application considering the measures they are using (whether proprietary standards, industry technical standards, or a combination of both), to prevent access to the ECM. At a minimum, this documentation should describe in sufficient detail the measures that a manufacturer has used to: prevent unauthorized access; ensure that calibration values, software, or diagnostic features cannot be modified or disabled; and respond to repeated, unauthorized attempts at reprogramming or tampering. Section XII.A.2 of this preamble describes our proposed new section 40 CFR 1068.50 to codify a set of provisions that are consistent with current industry best practices with respect to adjustable parameters. Additional discussion can be found in Chapter 2 of the draft RIA.

3. Serviceability

Defective designs and tampering can contribute significantly to increased in-use emissions. EPA has warranty provisions and tampering prohibitions in place to address such issues. Mal-maintenance, which includes delayed or improper repairs and delayed or unperformed maintenance, also increases in-use emissions and can be intentional (e.g., deferring repairs due to costs) or unintentional (e.g., not being able to diagnose the actual problem and make the proper repair). Mal-maintenance (by owners or repair facilities) can result from:

• Difficulty and high costs to diagnose and repair
• Inadequate troubleshooting guides and maintenance instructions
• Limited access to maintenance information and specialized tools to make repairs

Vehicle owners, repair technicians, and manufacturers all play important and distinct roles in achieving intended in-use emission system performance and preventing mal-maintenance. Vehicle owners are expected to properly maintain the engines, which includes performing preventative maintenance, scheduled maintenance (e.g., maintaining adequate DEF supply for their diesel engines' aftertreatment), and completing repairs when components or systems degrade or fail. Repair technicians are expected to properly diagnose and repair malfunctioning emission systems. Finally, manufacturers play a key role in providing both owners and repair technicians with access to the information they need to perform such expected maintenance and repairs.

EPA published several rules between 1993 and 2003 that improved service information access and required onboard diagnostic (OBD) systems for light-duty vehicles up to 14,000 lb GVWR. In 2009, EPA finalized similar requirements for the heavy-duty industry to ensure that manufacturers make diagnostic and service information available to any person repairing or servicing heavy-duty vehicles and engines (74 FR 8309, February 24, 2009). The service information requirements include information necessary to make use of the OBD system and instructions for making emission-related diagnoses and repairs, training access, technical service bulletins, and other information generally available to their franchised dealers or other persons engaged in the repair, diagnosing or servicing of motor vehicles. Since this time, manufacturers have entered into a service-related agreement through trade associations representing the aftertreatment repair industry and truck and engine manufacturers, highlighting concerns over intellectual property and their continued need for proprietary tools. EPA is not proposing changes to service information regulations at this time. While the service information regulations were an important first step in improving serviceability, as emission control systems have continued to develop, it has become necessary to consider other improvements that can be made to support in-use maintenance and repair practices. CAA section 207(c)(3)(A) requires manufacturers to provide instructions for the proper maintenance and use of a vehicle or engine by the ultimate purchaser and requires such instructions to correspond to EPA regulations. Section 207(c)(3)(A) also requires manufacturers to provide notice in those instructions that maintenance, replacement, or repair of emission control devices and systems may be performed by any automotive repair establishment or individual using any automotive part which has been certified as provided in section 207(a)(2). Section 207(c)(3)(B) requires that these instructions shall not include any condition on the ultimate purchaser's using, in connection with such vehicle or engine, any component or service (other than a component or service provided without charge under the terms of the purchase agreement) which is identified by brand, trade, or corporate name; or directly or indirectly distinguishing between service performed by the franchised dealers of such manufacturer or any other service establishments with which such manufacturer has a commercial relationship, and service performed by independent automotive repair facilities with which such manufacturer has no commercial relationship; unless EPA finds the vehicle or engine will function properly only if the component or service so identified is used in connection with such vehicle or engine, and that such a waiver is in the public interest.

Section 207(c)(3)(C) states that manufacturers must affix a permanent label indicating that the vehicle or engine is covered by a certificate of conformity and containing other information relating to control of motor vehicle emissions as prescribed by EPA regulations. Finally, section 202(m)(5) clarifies that manufacturers must provide this information promptly to anyone engaged in the repairing or servicing of motor vehicles or engines, except as specified. This section describes proposed regulatory amendments under these statutory provisions and are intended to improve serviceability, reduce mal-maintenance, and ensure owners are able to maintain emission performance throughout the entire in-use life of heavy-duty engines.

i. Current Repair and Maintenance Experiences

Continued maintenance issues can result in, among other things, owner dissatisfaction, which may cause some owners to remove or bypass emission controls. Any actions we can take to reduce maintenance issues could reduce incidents of tampering. In the ANPR, EPA requested comment on experiences with serviceability and received comment in three general categories: (1) Frustrations related to advanced emission control system reliability; (2) misdiagnosis and improper repair by professional facilities which lead to repeated trips to repair facilities and significant downtime, and (3) limited access to maintenance information which leads to the inability to self-diagnose problems.

Serviceability concerns affect all trucking operations, although different types of operators may experience these impacts in different ways. EPA received comments from trade organizations representing very large trucking fleets ( e.g., the American Trucking Associations, “ATA”), small fleets ( e.g., National Association of Small Trucking Companies, “NASTC”), and owner-operators ( e.g., Owner-Operator Independent Drivers Association, “OOIDA”), as well as from independent commenters, indicating that serviceability issues are one of the top concerns when operating trucks with advanced emission control systems. ATA commented that current emission control systems are still causing concerns for fleets and noted that in a recent study by ATA's Truck Maintenance Council, aftertreatment maintenance issues, serviceability, and ease of diagnostics were identified as major areas of concern by their members. NASTC submitted comments directly from their members indicating a number of concerns related to serviceability. OOIDA commented that their members have encountered various problems with emissions systems which have had a dramatic impact on their businesses including expensive visits to dealers, lost productivity, poor efficiency, and towing costs. A number of other commenters described their experiences and how improvements can be made to reduce cost and frustration. Trucking companies participating in a round table discussion in EPA's Region 7 expressed similar concerns about impacts to business as a result of delayed or missed deliveries, including lost customers, and possible legal or contract consequences.

In addition to operators, EPA received comments from state and local agencies supportive of improving access of maintenance information and service tools for fleets and owner-operators. For example, NACAA stated that EPA should work to increase access to the information and tools needed to repair the emission control systems on aging trucks, which is especially important for small businesses, small fleets, independent owner/operators, and rural operations, where access to dealer service networks can be a challenge.

a. Reliability of EPA 2010 Engines

We are keenly aware of significant discontent expressed by owners concerning their experiences with emission systems on engines compliant with EPA 2010 standards. EPA has also identified numerous Technical Service Bulletins submitted by OEMs to NHTSA's website documenting issues such as no trouble found, wiring concerns, or minor corrosion on connectors which can lead to inducement. Although significant improvements have been made to these systems since they were first introduced into the market, reliability and serviceability continue to cause concern. ATA commented that their members are experiencing problems with a wide variety of issues such as: Aftertreatment wiring harness failures, DEF nozzles plugging or over-injecting, NO_X sensor failures, defective DEF pumps and level sensors, systems being less reliable in rain and cold weather, more frequent required cleaning of DPFs, and problems related to DEF build-up. ATA also stated that their members have reported that mechanics at dealerships sometimes clear codes with no associated repairs being made. Many of these issues can also lead to severe engine derate and towing costs (see Section IV.D for further information on proposed inducement provisions, including revisions to policy currently in guidance). OOIDA commented that some of its members have experienced emission technology failures that caused their engines to quickly derate, placing truckers and other motorists in unsafe situations.

In addition to the comments highlighting problems related to wiring harness issues and sensor failures, a number of published articles have presented similar findings. For example, “Dealing with Aftertreatment Issues” in Fleet Equipment Magazine discusses how at least one OEM is focusing on improving issues with wiring and sensors “which are often the culprits in aftertreatment downtime.” A recent article from Transport Topics highlights how fleets are experiencing wiring issues and sensor failures that are creating problems that even sophisticated diagnostic tools cannot solve easily.

b. Misdiagnosis and Improper Repairs

Misdiagnosis can lead to the unnecessary replacement of parts without properly addressing the problem, which can result in additional breakdowns and tows with return trips to repair facilities for diagnostic service. ATA commented that several fleets are reporting the need for 'comeback' repairs and that while emissions-related training for diagnosis and repair work has improved, it is still severely lagging behind expectations. The NASTC describes problems some owners have experienced with repeated emission system component failures. In one example, an owner had to replace four NO_X sensors, two diesel exhaust fluid (DEF) filters, a DEF pump, a DPF, and a diesel oxidation catalyst (DOC) within only 6 months of purchasing a new truck. NASTC also described problems other owners experienced due to failures of NO_X sensors, DPF filters, DOCs, other emission-related sensors, and wiring harnesses, as well as repeated DEF doser injector pumps and valve failures. Other NASTC commenters described improper repair experiences resulting in trucks being down for weeks at a time. An independent commenter stated that repeated repairs in a 6-month time period resulted in loss of his truck and the ability to continue as an owner-operator.

c. Limited Access to Repair Facilities, Maintenance Information, and Service Tools

In response to the ANPR, EPA received numerous comments on difficulties associated with repairs of emission control systems. Many commenters indicated there is a substantial wait time to get a vehicle into a specialized repair facility, which, in some cases, was more than a week in addition to the time required to repair the vehicle. This wait time may be manageable if the vehicle remains operational, but can have a significant impact on an owner's ability to generate income from a vehicle if the truck is subject to an inducement and they are unable to use the vehicle until the repair is made. EPA received comments from the National Tribal Air Association and Keweenaw Bay Indian Community suggesting that service information and tools are not readily available and affordable for individual owners to diagnose and fix their own vehicles, and improved access can be especially important for small businesses, Tribes, and those in rural areas with less ready access to original equipment manufacturer dealer networks.

EPA received a number of comments on difficulties getting the right information or tools to repair vehicles outside of specialized repair facilities. ATA commented that their members report that in order to ensure proprietary tools are used, some manufacturers lock out certain diagnostic programs needed to further diagnose and reset systems after repairs, which ATA believes is a barrier to owners quickly diagnosing emission control system problems. ATA added that while some large fleets have added laptops in the field to help troubleshoot issues, fleets with more than one brand of truck may face significant expense to acquire multiple OEM software/diagnostic packages for these laptops. NASTC members noted that there are very few independent repair facilities that will repair emission systems problems, and given the long lead times at traditional repair facilities, a single fault code can remove a truck from service for more than a week. NASTC members also commented that diagnostic tools for owners are not affordable but are currently the only way to access diagnostic codes outside of a trip to a repair facility. OOIDA commented that according to a 2018 survey, 73 percent of their members perform repairs and maintenance on their own trucks. OOIDA added that being able to diagnose problems and repair equipment outside of dealerships is important for owner-operators and allows them to save time, avoid downtime, and reduce operating costs; however, they believe that restrictions built into existing trucks are preventing this practice. OOIDA supported an emphasis on serviceability improvements so that professional drivers can independently identify and repair problems with their engines and aftertreatment as much as possible.

ii. Proposed Maintenance Information for Improved Serviceability

In addition to labeling, diagnostic, and service information requirements, EPA is proposing to require important maintenance information be made available in the owner's manual. The owner's manual is a document or collection of documents prepared by the engine or vehicle manufacturer for the owner or operator to describe appropriate engine maintenance, applicable warranties, and any other information related to operating or maintaining the engine or vehicle. EPA is proposing to require additional maintenance information in the owner's manual as a way to improve factors that may contribute to mal-maintenance, resulting in better service experiences for independent repair technicians, specialized repair technicians, owners who repair their own equipment, and possibly vehicle inspection and maintenance technicians. Combined with our proposed modifications to onboard diagnostic requirements and proposed provisions for inducements, we expect these proposed serviceability provisions would improve owner experiences operating and maintaining heavy-duty engines and provide greater assurance of long-term in-use emission reductions by reducing likelihood of occurrences of tampering.

EPA is proposing changes to owner's manual and label requirements that would be mandatory for MY 2027 and later engines. The existing proposal would be voluntary for earlier model years, but we are seeking comment on making all or parts of this proposal mandatory as soon as MY 2024. We expect these changes would increase owner understanding of emission control systems, improve experiences at repair facilities, provide better access to information to help identify concerns, and enable owners to self-diagnose problems (especially important for aging trucks). Our proposal is intended to ensure consistent access to emission systems diagrams and part number information across the range of commercial vehicle engines and improve clarity in the information presented in those diagrams. Owner's manuals today include very detailed descriptions of systems such as radios and infotainment centers, fuse box and relay diagrams, and troubleshooting guides for phone connectivity features, but generally include limited information on emission control system operations. Given the importance and complexity of emission control systems and the impact to drivers for failing to maintain such systems ( e.g., inducements), EPA believes including additional information about emission control systems in the owner's manual is critical.

We are proposing to require manufacturers to provide more information concerning the emission control system in both the owner's manual and the emissions label. Our proposal would require the owner's manual to include descriptions of how the emissions systems operate, troubleshooting information, and diagrams. The emissions label would include an internet link to obtain this additional information. EPA has had similar requirements in the past, such as when EPA required vacuum hose diagrams to be included on the emission label to improve serviceability and help inspection and maintenance facilities identify concerns.

Specifically, as a part of the new 40 CFR 1036.125(h)(3)-(9) and (11), we propose that manufacturers provide the following additional information in the owner's manual:

• A description of how the owner can use the OBD system to troubleshoot problems and access emission-related diagnostic information and codes stored in onboard monitoring systems including information about the role of the proposed health monitor to help owners service their engines before components fail.
• A general description of how the emission control systems operate.
• One or more diagrams of the engine and its emission-related components with the following information:

○ The flow path for intake air and exhaust gas.

○ The flow path of evaporative and refueling emissions for spark-ignition engines, and DEF for compression-ignition engines, as applicable.

○ The flow path of engine coolant if it is part of the emission control system described in the application for certification.

○ The identity, location, and arrangement of relevant sensors, wiring, and other emission-related components in the diagram. Terminology to identify components would be required to be consistent with codes you use for the OBD system.

○ Expected pressures at the particulate filter and exhaust temperatures throughout the aftertreatment system.

• Exploded-view drawings to allow the owner to identify the part numbers and basic assembly requirements for turbochargers, aftercoolers, and all components required for proper functioning of EGR and aftertreatment devices including enough detail to allow a mechanic to replace any of those components.
• A basic wiring diagram for aftertreatment-related components including enough detail to allow a mechanic to detect improper functioning of those components.

• Statement instructing owners or service technicians where to find emission recall and technical repair information available without charge from the National Highway Traffic Safety Administration.

• Troubleshooting guide to address DEF dosing- and DPF regeneration-related warning signals that would be displayed in the cab or with a generic scan tool, including a description of the fault condition, the potential causes, the remedy, and the consequence of continuing to operate without remedy including a list of all codes that cause derate or inducement ( e.g., list SPN/FMI combinations and associated operating restrictions, see proposed requirements in 40 CFR 1036.110(b)(9)(vi)).

• For the DPF system, instructions on how to remove DPF for cleaning, criteria for cleaning the DPF including pressure drop across the filter, clean filter weight, pre-installed filter weight, a statement that DPF inlet and outlet pressures are available with a generic scan tool, and information on maintenance practices to prevent damage to DPFs.

We propose to include these eight additional provisions for all engine configurations, including hybrids, where applicable. EPA is seeking comment on these eight proposed additional provisions or other approaches to improve the serviceability of heavy-duty engine emission control systems. Finally, in 40 CFR 1036.135(c), EPA is proposing that manufacturers include a Quick Response Code or “QR Code” on the emission label that would direct repair technicians, owners, and inspection and maintenance facilities to a website which provides critical emissions systems information at no cost including: A digital copy of the owner's manual (or just the emissions section of the manual), engine family information, emission control system identification, and fuel and lubricant requirements (see proposed revisions in 40 CFR 1036.135). Many manufacturers already make digital owner's manuals available online. EPA recognizes that there may be a need to accommodate different information formats relating to the QR code link and requests comment on whether to include different options to achieve the same goals, and if so, what those options should be. The maintenance information we are proposing to add to the owner's manual is critical to making necessary information available promptly to any person performing emissions-related maintenance.

Including the proposed additional information in the owner's manual and emission label can increase an owner's understanding of emission systems operation and fault conditions. Providing owners and repair technicians access to diagrams describing system layout and operation can help reduce confusion where manufacturers may have different system configurations. For example, some configurations may have the DPF in front of the SCR catalyst, while others may have it behind the SCR catalyst. Lack of easily accessible diagrams can lead to mal-maintenance and improper repair where components that need to be replaced are not identified properly. For example, some manufacturers label exhaust gas temperature (EGT) sensors generically such as EGT1 and EGT2 and the positioning of these sensors may differ or be reversed for the same engine model installed on vehicles with slightly different frame configurations. If a technician is unfamiliar with this change, they may replace the wrong EGT which would likely result in a repeat visit to a repair facility. Similarly, a DPF temperature sensor may be generically labeled “Exhaust Temperature Sensor” and may be shown on an EGR parts diagram rather than a DPF parts diagram, making it difficult to correctly identify replacement parts. With an easily accessible parts diagram, owners, parts counter specialists, and repair technicians can more quickly identify the correct parts to replace which would save time and eliminate frustration, especially where a truck is in an inducement. EPA is also seeking comment on the need to require standardization of terminology for certain components in the proposed labeling and owner's manual provisions to further reduce confusion for owners and technicians performing repairs. For example, some manufacturers call the DOC outlet temperature a DPF inlet temperature. Lack of standardization, including naming conventions and data output parameter scaling ( e.g., NO_X sensor output scaling may vary between manufacturers), may lead to confusion and inefficiencies when seeking replacement parts and performing troubleshooting and repairs. SAE J2403 “Medium-Heavy Duty E/E System Diagnosis Nomenclature” is designed to standardize nomenclature of components and how systems with multiple sensors ( e.g., multiple EGT sensors) should be numbered starting from the same place (e.g., starting at the engine). CARB requires that, to the extent possible, certification documentation shall use SAE J1930 or J2403 terms, abbreviations, and acronyms. EPA is seeking comment on whether this standard should be incorporated and required for use in naming certain emission components such as exhaust temperature sensors as a part of certification, maintenance instructions, diagnostic, or other serviceability-related requirements.

EPA seeks comment on other pertinent information that should be included in owner's manuals so that owners can more easily understand advanced emission control system operation and precautions that should be taken in order to maintain them. To the extent EPA can ensure this information is harmonized among manufacturers, we believe this could improve owner, operators, parts counter specialist, and repair technician experiences and reduce frustration which can lead to an incentive to tamper.

iii. Request for Comments on Maintenance and Operational Information for Improved Serviceability of Electric Vehicles

EPA is requesting comment on several potential serviceability requirements for BEV and FCEV technologies. Many of these potential serviceability provisions are similar to those proposed in Section IV.B.3.ii for CI and SI engines but are specific to these technologies that do not require a combustion engine or emissions aftertreatment system. As noted in the introduction of Section III.A, under 40 CFR 86.016-1(d)(4), heavy-duty BEV and FCEV manufacturers currently use good engineering judgment to apply the criteria pollutant requirements of part 86, Subpart S, including maintenance provisions.

We are requesting comment on seven categories of potential requirements for BEV and FCEV serviceability: (1) Labeling, (2) purchaser guidance, (3) maintenance information, (4) maintenance information requirements concerning the use of a standardized connector and making malfunction codes and powertrain parameters accessible, (5) onboard vehicle signals for service and repair technicians, (6) information on battery energy used per trip, and (7) battery information to facilitate battery recycling. We request comment on whether each of these categories individually or in combination should be finalized to support owners and repair technicians in maintaining and repairing BEV and FCEV technologies, or if alternative provisions suggested by commenters would better support these technologies while minimizing burden to manufacturers. Each of these categories of potential requirements is based on provisions of the 2019 CARB Zero Emissions Powertrain Certification (ZEP Certification), which imposes requirements on manufacturers choosing to generate NO_X emission credits under the CARB Omnibus rule. We believe that adopting an approach based on the CARB ZEP Certification program would provide manufacturers with consistency across the country. Consistent with the ZEP Certification requirements, EPA believes that the maintenance and operational information described in this section could help potential BEV and FCEV purchasers to understand the possible operational impacts of these technologies on their businesses, as well as ensure the vehicles are supported during their use in the field. Each of the areas in which we are requesting comment is briefly discussed immediately below.

For the first area (labeling), as specified in the current 40 CFR 1037.125, all vehicle manufacturers currently must affix a label to each vehicle with information such as manufacturer name, vehicle certification family, and build date; however, some of the information is specific to vehicles propelled by an engine ( e.g., 40 CFR 1037.125(c)(6) requires manufacturers to specify the emission control system). We request comment on whether there is additional information specific to BEVs and FCEVs that would be useful to include on the vehicle label for repair technicians, owners, and inspection and maintenance professionals. We also request input from commenters on whether we should require a QR code on BEV and FCEV labels, similar to the proposed QR code requirement in 40 CFR 1036.135(c). Specifically, the BEV or FCEV label could include a QR code to a website which would direct repair technicians, owners, or inspection and maintenance facilities to a website with information including: A digital copy of the owner's manual, vehicle family information, and powertrain identification. Commenters are encouraged to provide details on how any suggestions for additional information would help vehicle owners with the repair and maintenance of BEVs or FCEVs, as well as the potential burden to manufacturers to include such information on the vehicle label.

For the second area (purchaser guidance), we request comment on whether EPA should require BEV and FCEV manufacturers to provide purchaser guidance information to potential owners on aspects of BEV or FCEV ownership that may differ from owning a vehicle with a CI or SI engine. Immediately below, we provide several examples of the types of information that manufacturers could provide in purchaser guidance if we were to finalize such a requirement in this rule or another future rulemaking. For instance, purchaser guidance could include the range the vehicle is capable of driving over a specified duty-cycle, top speed, and maximum grade. As another example, manufacturers could describe how vehicle load, ambient temperatures, and battery degradation impact range, top speed, or maximum grade. Manufacturers could also provide potential purchasers estimates of the time required for maintenance and repairs of common malfunctions, as well as potential vehicle transportation costs. Finally, manufacturers could clearly describe any warranty coverage of the battery and other key powertrain components that would be covered (see Section IV.B.1.iv.b for our proposed warranty requirements). To minimize manufacturer burden, EPA could provide an example statement in 40 CFR part 1037 that manufacturers could choose to use if they attest that the statement is accurate for their vehicle; the example statement could largely mirror the statement that was proposed by CARB under the 2019 CARB ZEP Certification and subsequently adopted into current CARB regulations for GHG emissions from 2014 and later model vehicles. While an example statement provided by EPA would minimize manufacturer burden, it would also, by necessity, be more generic and not reflect parameters specific to a given vehicle model ( e.g., range). We encourage commenters to provide input on the potential benefits of manufacturers providing such purchaser guidance relative to the potential burden to manufacturers to provide such guidance.

For the third area (maintenance information), we request comment on whether EPA should require BEV and FCEV manufacturers to make additional maintenance information available to owners and repair technicians. Under the current 40 CFR 1037.125(f) manufacturers make the service manual and any required service tools available to third-party repair facilities at reasonable cost; however, we request comment on any information specific to BEVs or FCEVs that would be important for repair technicians in maintaining and repairing BEV and FCEV technologies. In addition, we request comment on whether EPA should require manufacturers to describe in their certification application the monitoring and diagnostic strategies they use for the BEV or FCEV; these strategies would also be included in their service manuals. In addition to being similar to existing requirements for vehicles powered by an engine, this potential provision would be consistent with the ZEP Certification requirements.

For the fourth area (standardized connector and accessible malfunction codes and powertrain parameters), we request comment on whether EPA should require that BEV and FCEV manufacturers use a standardized connector that is compatible with automotive scan tools, and further that all malfunction codes and key powertrain parameters must be readable by a generic automotive scan tool. Commenters are encouraged to provide information on whether the use of a standardized connector would facilitate repair of BEVs and FCEVs, and the utility of making all malfunction codes and key powertrain parameters readable by a generic scan tool. We also request stakeholder input on the potential burden to manufacturers to make the standardized connector, malfunction codes, and key powertrain parameters accessible.

For the fifth area (onboard vehicle signals), we request comment on whether EPA should require manufacturers to make powertrain monitoring or diagnostic signals publicly accessible to repair and service technicians to facilitate BEV and FCEV maintenance or repair. In Section IV.I we request comment on whether and how manufacturers who choose to generate NO_X emission credits could make information on battery or fuel cell durability readily accessible; here we request comment on other potential parameters that may be useful for maintaining and repairing BEVs and FCEVs:

• Energy Storage System State of Charge (SOCE)

○ Function: Indicate the remaining energy left in the battery(ies). Would allow users to identify battery degradation or failure that may require maintenance or repair of the battery or powertrain systems.

• Energy Storage System State of Range (SOCR)

○ Function: Indicate the remaining range of the battery(ies). Would allow users to identify battery degradation or failure that may require maintenance or repair of the battery or powertrain systems.

• Drive Motor System Efficiency

○ Function: Compare the energy use of the drive motor from the current state to the as manufactured state to see degradation over time (e.g., 100 percent being as manufactured and decreasing as the performance of the drive motor decreases), or failure. Would allow first owner and secondhand buyers to identify degradation in the electric motor.

• Battery Temperature

○ Function: Identify battery temperature. Would inform repair technicians about when battery thermal management system may need repair ( e.g. , identify when battery thermal management system degradation impacts range or charge rate).

• Percent Regenerative Braking

○ Function: Measure the amount of regenerative braking relative to total capacity for capturing energy from regenerative braking. Information could provide insight on when potential maintenance or repair is needed for systems related to regenerative braking, as well as feedback to users on driving behavior that results in greater energy capture from regenerative braking.

• Charging Rate

○ Function: Check performance of the inverter/converter and batteries. Would allow service repair technicians to identify when inverter/converter, batteries or other components may need repair.

• Charging System Performance

○ Function: Identify current charge rate at optimal battery temperature relative to charge rate at the time of manufacture. Would allow service technicians to identify degradation or failure in key components of the charging system.

Commenters are encouraged to provide input on whether each of the listed parameters would be useful, or if there are additional parameters that would be informative. We request that commenters provide any additional specifics of why each signal would be useful for EPA to include in the final rule, or as part of other future rulemakings. We also invite stakeholder input on whether EPA should recommend a common language for BEV and FCEV communication protocols ( e.g., J1979-2). Note that we are not requesting comment on whether and how manufacturers would utilize signals or a common communication protocol to monitor or diagnose problems. Commenters are encouraged to provide information on why additional onboard vehicle information would be important for BEV and FCEV repairs, and how EPA suggesting a common communication protocol would, or would not, be useful for the industry.

For the sixth area (battery energy used per trip), we request comment on whether manufacturers already utilize onboard vehicle sensors that could provide estimates of energy consumption per trip, and whether manufacturers could readily provide energy consumption per trip information through a dashboard display. We further request comment on whether battery energy used per trip would support users understanding normal variance in battery performance due to factors such as terrain, driving behavior, and temperature, versus battery performance degradation that would necessitate maintenance or repair of the powertrain. EPA will consider information provided by commenters to evaluate the potential benefits of users understanding when a battery may need repair relative to the potential burden to manufactures to make such information available to users.

For the seventh area, we request comment (battery information) on the utility and feasibility of adding a battery information requirement for BEVs and FCEVs. If we were to include a battery information requirement in the final rule, then manufacturers would: (1) Briefly describe in their owner's manual how to handle the battery after it is no longer capable of providing sufficient energy or power to the vehicle ( e.g., identify alternative uses and safe disposal methods for the battery), and (2) affix a label on the battery, and include in the owner's manual, information necessary to recycle the battery ( e.g., manufacturer, chemistry, voltage, hazard statement, QR code to a website for additional details). We believe such battery information would be important for users to appropriately re-purpose, recycle, or otherwise dispose of the battery, and thereby minimize total environmental impact of the BEV or FCEV. Commenters are encouraged to provide information on whether such battery information would facilitate users identifying alternative uses for the battery or otherwise recycling the battery. We are also interested in information on the feasibility of vehicle manufacturers having sufficient information from battery suppliers to provide information on battery handling at the end of its life in a vehicle. EPA will consider information provided in comments and weigh the potential environmental benefits of users having battery information with the potential burden to manufacturers to provide such information.

iv. Other Emission Controls Education Options

In addition to our proposals to provide more easily accessible service information for users, we are seeking comment on whether educational programs and voluntary incentives could lead to better maintenance and real-world emission benefits. We received comments in response to the ANPR supportive of improving such educational opportunities to promote an understanding of how advanced emission control technologies function and the importance of emissions controls as they relate to the broader economy and the environment. Some commenters were generally supportive of using educational programs and incentives to improve maintenance practices. Commenters generally agreed that there are actions EPA could take to reduce the misinformation surrounding advanced emission control systems and that any action that EPA could take to improve access to easily-understandable maintenance information would be helpful. NADA commented that they would “welcome new emission control outreach and incentives to combat misperceptions that can lead to emissions tampering or mal-maintenance.” The Motor and Equipment Manufacturers Association (MEMA) commented that priority should be given to improving education and training offered to service facilities and technicians to reduce the misdiagnoses of faulty emission components where “it is a common diagnostic technique in service repair shops to continually swap out emissions components until the problem goes away.” Lubrizol suggested that EPA provide education to ensure fleets understand the proper lubricants required to maintain engines.

We seek comment on the potential benefits of educational and/or voluntary, incentive-based programs such as EPA's SmartWay program and how such a program could be designed and implemented.

4. Rebuilding

Clean Air Act section 203(a)(3) prohibits removing or rendering inoperative a certified engine's emission controls which typically includes being paired with properly functioning aftertreatment devices. The regulation at 40 CFR 1068.120 describes how this tampering prohibition applies for engine rebuilding and other types of engine maintenance. The regulation generally requires that rebuilders return a certified engine to its original configuration and keep records to document that the rebuilder had a reasonable technical basis for believing that the rebuilt engine's emission control system performs at least as well as the original design.

Since the rebuilding provisions in 40 CFR 1068.120 broadly apply to everyone involved in restoring a rebuilt engine to its certified configuration, to the extent that vehicle owners or others remove an engine from and install a rebuilt engine in a heavy-duty highway vehicle, we consider those steps to be part of the rebuilding process.

We are not proposing new or modified rebuilding provisions in this rule. However, we intend to continue to monitor rebuilding practices and may develop updated regulatory provisions in a future rulemaking.

5. Maintenance

Consistent with the CAA and existing regulations, our proposed standards would apply over the applicable useful life. Manufacturers perform testing to demonstrate that engines will meet emission standards over the full useful life. Manufacturers may perform scheduled maintenance on their test engines only as specified in the owner's manual. As part of the certification process, manufacturers must get EPA approval for such scheduled maintenance, which is also subject to minimum maintenance intervals as described in the regulations. In this section, we describe the updated maintenance provisions we are proposing for heavy-duty highway engines. Section IV.F of this preamble summarizes the current the durability demonstration requirements and our proposed updates.

Our proposed maintenance provisions, in a new section 40 CFR 1036.125, combine and amend the existing criteria pollutant maintenance provisions from 40 CFR 86.004-25 and 86.010-38. Similar to other part 1036 sections we are adding in this proposal, the structure of the new 40 CFR 1036.125 is consistent with the maintenance sections in the standard-setting parts of other sectors ( e.g., nonroad compression-ignition engines in 40 CFR 1039.125). In 40 CFR 1036.205(i), we are proposing to codify the current manufacturer practice of including maintenance instructions in their application for certification such that approval of those instructions would be part of a manufacturer's certification process. We are also proposing a new paragraph 40 CFR 1036.125(h) outlining several owner's manual requirements, including migrated and updated provisions from 40 CFR 86.010-38(a). For example, proposed 40 CFR 1036.125(h)(2) expands on the current requirement for manufacturers to describe the documentation owners need to provide to show maintenance occurred, by specifying that maintenance instructions must clearly state how to “properly maintain and use” the engine. The new paragraph (h)(2) provides a clearer connection to the regulatory requirements for warranty and defect reporting.

This section summarizes maintenance updates recently adopted by CARB and introduces our proposed provisions to clarify the types of maintenance, update the options for demonstrating critical emission-related maintenance will occur and the minimum scheduled maintenance intervals for certain components, and outline specific requirements for maintenance instructions.

i. Recent Updates to CARB Maintenance Regulations

In two recent rulemakings, CARB updated their maintenance regulations and we considered CARB's approach when designing our maintenance provisions for this proposal. In its Step 1 warranty program, CARB lengthened the minimum allowable maintenance intervals for heavy-duty diesel engines to reflect current industry norms for scheduling replacement of emissions-related parts. CARB stated that this change limits manufacturers' ability to transfer the liability for part replacements to vehicle owners for emissions-related parts during the lengthened warranty periods, further strengthening warranty coverage.

CARB staff surveyed owner's manuals for all 2016 California-certified on-road heavy-duty diesel engines and compiled the intervals manufacturers published for specific emission-related components. The maintenance intervals published in the owner's manuals were at or above the minimum intervals that currently apply for emission-related components. For MY 2022 and later HD diesel engines, CARB updated their minimum scheduled maintenance intervals to match the shortest ( i.e. , most frequent) interval from those published values for each component. If no manufacturer published an interval for a given component, CARB set the minimum maintenance interval for that component to match the current useful life mileage ( i.e., 435,000 miles for HHDD engines). CARB's Step 1 program also provides that manufacturers cannot schedule replacements for turbochargers, DPF elements, catalyst beds, or exhaust gas recirculation systems during the useful life of the engine unless the manufacturer agrees to pay for the replacements. These four emission-related components were chosen due to their direct emissions impact or high cost to replace. Furthermore, CARB clarified that there shall be no scheduled maintenance interval throughout the applicable useful life for sensors or actuators that are integrated with the turbocharger or exhaust gas recirculation (EGR) valve/cooler components, as these parts cannot easily be replaced without removing the larger systems from the engine. Other sensors and actuators that are necessary for the proper function of other emissions-critical systems or are not integrated with the turbocharger or EGR systems can be included on a maintenance schedule at a minimum interval of 150,000 miles.

CARB's HD Omnibus rulemaking did not include further updates to the maintenance provisions for diesel engines but addressed HD Otto-cycle engines and hybrid vehicles. Similar to their strategy to identify maintenance intervals for diesel engines, CARB surveyed owner's manuals for 2018 California-certified HD Otto-cycle engines and updated the minimum maintenance intervals for MY 2024 and later HD Otto-cycle engines based on the shortest intervals published. For gasoline vehicles, EGR systems and catalyst beds were designated “not replaceable” components. CARB further clarified that the same minimum intervals apply to diesel- and Otto-cycle engines used in hybrid vehicles.

ii. Types of Maintenance

Our proposed new 40 CFR 1036.125 clarifies that maintenance includes any inspection, adjustment, cleaning, repair, or replacement of components and, consistent with 40 CFR 86.004-25(a)(2), broadly classifies maintenance as emission-related or non-emission-related and scheduled or unscheduled. We propose to define the following five types of maintenance that manufacturers may choose to schedule:

• Critical emission-related maintenance
• Recommended additional maintenance
• Special maintenance
• Noncritical emission-related maintenance
• Non-emission-related maintenance

We are proposing to define these maintenance categories to distinguish between the types of maintenance manufacturers may choose to recommend to owners in maintenance instructions, identify the requirements that apply to maintenance performed during certification durability demonstrations, and clarify the relationship between the different types of maintenance, emissions warranty requirements, and in-use testing requirements. The proposed provisions described in this section specify the conditions for scheduling each of these five maintenance categories. Unscheduled maintenance (i.e., repair of failed components) is unpredictable and would not be included in a manufacturer's maintenance instructions or durability demonstration.

A primary focus of the current and proposed maintenance provisions is critical emission-related maintenance. Critical emission-related maintenance includes any adjustment, cleaning, repair, or replacement of emission-related components that manufacturers identify as having a critical role in the emission control of their engines. Consistent with the current 40 CFR 86.004-25(b)(6)(ii), our proposed 40 CFR 1036.125(a)(1) allows manufacturers to schedule critical emission-related maintenance in their maintenance instructions based on the manufacturer meeting two conditions: The manufacturer demonstrates the maintenance is reasonably likely to occur on in-use engines, and the recommended intervals are at least as long as the minimum intervals set by EPA. We describe our proposed conditions for demonstrating critical emission-related maintenance will occur in Section IV.B.5.iii. In Section IV.B.5.iv, we describe our proposal to update the minimum maintenance intervals currently specified in 40 CFR 86.004-25(b)(3) and (4) for certain critical emission-related components. For new technology, not included in the list of proposed components with specified minimum maintenance intervals, we are proposing to migrate and update the process specified in 40 CFR 86.094-25(b)(7), as described in Section IV.B.5.v.

The four other types of maintenance would require varying levels of EPA approval. In 40 CFR 1036.125(b), we propose to define recommended additional maintenance as maintenance that manufacturers recommend owners perform for critical emission-related components in addition to what is approved for those components under 40 CFR 1036.125(a). A manufacturer may recommend that owners replace a critical emission-related component at a shorter interval than the manufacturer received approval to schedule for critical emission-related maintenance; however, the manufacturer would have to clearly distinguish their recommended intervals from the critical emission-related scheduled maintenance in their maintenance instructions. As described below, recommended additional maintenance is not performed in the durability demonstration and cannot be used to deny a warranty claim, so manufacturers would not be limited by the minimum maintenance intervals or need the same approval from EPA by demonstrating the maintenance would occur. Special maintenance, proposed in 40 CFR 1036.125(c), would be more frequent maintenance approved at shorter intervals to address special situations, such as atypical engine operation. Manufacturers would clearly state that the maintenance is associated with a special situation in the maintenance instructions provided to EPA and owners. Our proposed definition of noncritical emission-related maintenance, which is based on 40 CFR 86.010-38(d), includes inspections and maintenance that is performed on emission-related components but is considered “noncritical” because emission control will be unaffected. As specified in proposed 40 CFR 1036.125(d), manufacturers may recommend noncritical emission-related inspections and maintenance in their maintenance instructions if they clearly state that it is not required to maintain the emissions warranty. Finally, we define “non-emission-related maintenance” as maintenance unrelated to emission controls (e.g., oil changes) in proposed 40 CFR 1036.125(e). We propose that manufacturers' maintenance instructions can include any amount of nonemission-related maintenance that is needed for proper functioning of the engine.

Maintenance instructions play an important role in the service accumulation portion of a manufacturer's durability demonstration. We currently require that all emission-related scheduled maintenance during durability testing occur on the same schedule as specified in the maintenance instructions for the purchaser. When accumulating equivalent miles on an engine, manufacturers are currently allowed to perform maintenance according to their maintenance instructions. In this proposal, we clarify how this relates to the specific types of maintenance in proposed 40 CFR 1036.125. Consistent with current maintenance provisions, we propose that manufacturers can perform critical emission-related maintenance at their approved schedules during a durability demonstration. Since the proposed recommended additional maintenance provisions do not include the same requirement to demonstrate the maintenance will occur in-use, manufacturers could not perform recommended additional maintenance during their durability demonstration. Special maintenance would also not be performed during a durability demonstration, since laboratory-based testing does not reflect atypical operation. We propose that manufacturers may perform noncritical emission-related inspections on their engines during their durability demonstration at any frequency, but could only adjust, clean, repair, or replace a component in response to an inspection if scheduled maintenance is approved for that component. We propose manufacturers can perform any amount of nonemission-related maintenance that is needed for proper functioning of the engine during durability testing.

The current general warranty requirements of 40 CFR 1068.115(a) allow a manufacturer to deny warranty claims for failures resulting from improper maintenance or use. We are proposing a new owner's manual requirement for manufacturers to specifically identify the steps an owner must take to properly maintain the engine, including documentation a manufacturer may require for an owner to demonstrate the maintenance occurred. In 40 CFR 1036.125, we propose to clarify the relationship between the different types of maintenance and emissions warranty requirements, and specify when manufacturers must note in their maintenance instructions (i.e., owner's manual) if a maintenance type cannot be used as the basis to deny a warranty claim. We expect manufacturers would only schedule critical emission-related maintenance and make the effort to demonstrate the maintenance is likely to occur in-use for components that they recognize are strongly connected to emission performance. As a result, our current maintenance provisions allow, and our proposed provisions would continue to allow, manufacturers to deny warranty claims if owners do not perform critical emission-related maintenance at the recommended schedule, as specified in 40 CFR 1068.115. Failure to perform recommended additional maintenance could potentially impact emissions, but manufacturers would not be able to deny a warranty claim if owners do not perform it, because manufacturers would not have taken the extra steps to have it approved as critical Manufacturers would be able to deny warranty claims if an owner did not perform the special maintenance after it was determined that the engine was operated in conditions that meet the special situation described in the maintenance instructions. In contrast, manufacturers would not be able to deny a warranty claim citing “improper maintenance or use” for atypical operation if an owner follows the corresponding special maintenance instructions. We propose that failure to perform noncritical emission-related maintenance and nonemission-related maintenance cannot be used to deny emissions warranties.

Since failure to perform maintenance may also impact emissions when the engine is in use, we have also identified the relationship between the maintenance types and in-use testing. Compression-ignition engine manufacturers are subject to off-cycle standards for in-use engines. As part of the proposed manufacturer-run testing program in subpart E, we specify that manufacturers can select vehicles and engines for testing based on proper maintenance and use (see 40 CFR 1036.410(b)(2)). In 40 CFR 1036.125, we propose that if recommended additional maintenance or noncritical emission-related maintenance is not performed on an engine, it does not disqualify the engine from in-use testing. Manufacturers may reject an engine for in-use testing if the other types of maintenance (i.e., critical emission-related maintenance, special maintenance, or nonemission-related maintenance) were not performed, consistent with current provisions in 40 CFR 86.1908.

iii. Critical Emission-related Maintenance Demonstration

One of the current conditions for allowing scheduled maintenance to be performed during the durability demonstration is that manufacturers demonstrate the maintenance is reasonably likely to be performed in-use. For critical emission-related scheduled maintenance, we are generally including these same requirements in our proposed new paragraph 40 CFR 1036.125(a)(1), with clarifications noted below.

Under proposed 40 CFR 1036.125(a)(1)(i), manufacturers could demonstrate that the critical maintenance is reasonably likely to occur in-use on the recommended schedule by providing data showing that the engine's performance unacceptably degrades if the maintenance is not performed, consistent with 40 CFR 86.004-25(a)(6)(ii)(A). In this proposal, we clarify that this paragraph is intended to cover emission control technologies that have an inherent performance degradation that coincides with emission increases, such as back pressure resulting from a clogged DPF, and is not intended to apply to inducements where a manufacturer-specified performance derate is triggered in response to a detected or predicted emission increase. We are proposing a separate statement in 40 CFR 1036.125(a)(1) that points to the new proposed inducement provisions noting that we would accept DEF replenishment as reasonably likely to occur if an engine meets the specifications in proposed 40 CFR 1036.111.

Under proposed 40 CFR 1036.125 (a)(1)(ii) and consistent with 40 CFR 86.004-25(a)(6)(ii)(C), manufacturers could demonstrate a reasonable likelihood that the critical maintenance will be performed in-use by including a system that displays a visible signal to alert drivers that maintenance is due. We are proposing additional criteria for use of this visible signal, including that it be continuously displayed while the engine is operating and not easily eliminated without performing the specified maintenance. We request comment on this proposal and any additional criteria we should consider before approving a visible signal as a method to ensure critical emission-related scheduled maintenance is performed.

Under proposed 40 CFR 1036.125(a)(1)(iii), manufacturers could present survey data showing that 80 percent of engines in the field receive the specified maintenance. We are maintaining this existing option (see paragraphs (B) and (D) of 40 CFR 86.004-25(a)(6)(ii)) in our proposal but note that manufacturers have not presented survey data related to scheduled maintenance in recent years. We request comment on this option and any updates we should consider, including how telematic data could be applied and if 80 percent continues to be an appropriate threshold.

We are also proposing in 40 CFR 1036.125(a)(1)(iv) to continue an existing provision in 40 CFR 86.004-25(a)(6)(ii)(E) that a manufacturer may rely on a clear statement in their maintenance instructions for owners that it will provide the critical maintenance free of charge. Finally, we propose to continue to allow manufacturers to present other options for approval by EPA to demonstrate that critical emission-related maintenance is reasonably likely to occur (see proposed 40 CFR 1036.125(a)(1)(v) and current 40 CFR 86.004-25(a)(6)(ii)(F)).

iv. Emission-Related Components and Minimum Maintenance Intervals

Manufacturers, with EPA approval, may define scheduled maintenance for emission-related components, which would be included in maintenance instructions directing owners to adjust, clean, or replace components at specified intervals. The current regulations in 40 CFR 86.004-25(b) specify minimum maintenance intervals for emission-related components, such that manufacturers may not specify more frequent maintenance than we allow. We propose to migrate and update the minimum maintenance intervals from part 86, subpart A to 40 CFR 1036.125(a). These proposed minimum intervals would apply for the scheduled adjustment, cleaning, or replacement of many common critical emission-related components, as described in this section. We are proposing not to migrate the list of critical emission-related components currently specified in 40 CFR 86.004-25, and instead are proposing a new definition of “critical emission-related component” in 40 CFR 1068.30 that refers to 40 CFR part 1068, appendix A.

As part of the migration to part 1036, we are proposing to update the lists of components with minimum maintenance intervals to more accurately reflect components in use today. We are not including carburetors, idle mixture, and particulate trap oxidizers in the proposed 40 CFR 1036.125 as these components are obsolete. Our proposed language replaces the part 86 diesel particulate trap intervals with a more general “particulate filtration system” that can apply to particulate filters intended for SI or CI engines. We also no longer specify an interval for electronic engine control units as we are unaware of any scheduled maintenance for those components. Our proposed minimum maintenance intervals for each emission-related component or system continue to apply to any associated sensors or actuators. We are further proposing that these intervals also apply to any hoses, valves, and wiring connected to the component or system, such that manufacturers would ensure that all parts necessary to keep the component functional, including wires and wiring harnesses, remain durable throughout useful life or schedule appropriate maintenance to address any durability concerns.

We propose not to migrate the 100,000-mile minimum interval for Spark-ignition HDE evaporative emission canister to 40 CFR 1036.125, since evaporative emission control systems are covered under the vehicle provisions of part 1037. Similarly, we propose that components in the refueling emission control system that would be used to meet the proposed refueling standards for certain SI HDE, including the carbon canisters, filler pipes and seals, refueling flow controls, purge systems, and related wiring, actuators, and sensors, would also be covered under the maintenance provisions of part 1037.

We are proposing to add minimum scheduled replacement intervals for other components and systems that correspond to technologies we expect to be considered by manufacturers for meeting our proposed standards. In general, the proposed minimum replacement intervals are set at the current useful life for each engine class, since we do not have data indicating that manufacturers are scheduling maintenance for these components within the current useful life. We are proposing NO_X sensor minimum intervals at the current useful life mileages for the Light, Medium, and Heavy HDE classes. We also propose to add minimum intervals for replacing a rechargeable energy storage system (RESS) in hybrid vehicles. Our proposed minimum intervals for RESS equal the current useful life for the primary intended service classes of the engines that these electric power systems are intended to supplement or replace. We are not specifying distinct minimum intervals for the electric power system components of BEVs and FCEVs; instead, manufacturers could request approval for an interval using 40 CFR 1037.125(a).

Considering our proposed lengthened useful life periods, we reevaluated the current minimum maintenance intervals for replacing components and are proposing to extend the replacement intervals such that they reflect the scheduled maintenance of components today. Table IV-11 summarizes the minimum replacement interval mileages we are proposing in a new table in 40 CFR 1036.125(a). Similar to the minimum maintenance interval approach adopted by CARB in their recent rulemakings (see Section IV.B.5.i), we are proposing to base our revised minimum replacement intervals on the scheduled maintenance submitted by engine manufacturers for certifying recent model year engines. We believe it is appropriate to account for replacement intervals that manufacturers have already identified and demonstrated will occur for these components and we are proposing replacement intervals for these components that align with the shortest mileage interval ( i.e. , most frequent maintenance) of the published values. We propose to update the minimum replacement mileages for remaining components that currently do not have specified maintenance intervals in the current list from the current 100,000 or 150,000 miles to the current useful life mileage for each primary intended service class. Since manufacturers are not scheduling replacement of these other components within the current useful life of their engines today, we do not expect manufacturers would have a technical need to do so in the future. We are not proposing to update the maintenance intervals for adjusting or cleaning critical emission-related components. These intervals are proposed to be migrated, with updated component names consistent with the proposed replacement intervals, from 40 CFR 86.004-25 into a proposed new table in 40 CFR 1036.125(a). Consistent with current regulations, our proposed 40 CFR 1036.125(a) would continue to allow manufacturers to seek advance approval for new emission-related maintenance they wish to include in maintenance instructions and perform during durability demonstration.

The minimum maintenance intervals presented in Table IV-11 and Table IV-12 are based on mileage, since equivalent mileage accumulation is the parameter used for the durability demonstration. Consistent with our current maintenance provisions, we are proposing corresponding minimum hours values based on a 33 miles per hour vehicle speed ( e.g. , 150,000 miles would equate to 4,500 hours). We request comment on the conversion factor between mileage and hours, noting that hours would not apply to the manufacturers' durability demonstrations, but may impact the frequency of scheduled maintenance for owners with lower speed vehicle applications. Consistent with the current maintenance intervals specified in part 86, we are not proposing year-based minimum intervals; OEMs can use good engineering judgment if they choose to include a scheduled maintenance interval based on years in their owner's manuals, which is expected to only be used by a small number of infrequently operated vehicles. We request comment on the need to specify a minimum year-based interval, including data on average annual mileages to convert the minimum mileage intervals to years for each of the primary intended service classes.

We request comment on all components and systems presented in Table IV-11 and Table IV-12 and the corresponding minimum scheduled maintenance intervals. Specifically, we request data to support different interval values or specific components that should have intervals distinct from presented systems. We request comment on our proposal to update the list of components and systems, whether additional components should be considered, and if any of the listed components or systems should be more clearly defined. Additionally, if a commenter believes there is value in prioritizing or otherwise grouping emission control components, we encourage them to suggest criteria to classify the components. We request comment on the numeric values of the replacement intervals proposed, and our proposal to preserve the current minimum intervals for adjusting and cleaning components. Manufacturers and suppliers have shown an interest in developing modular emission controls that can be serviced more easily. We request comment on the specific emission control systems that may use modular components, criteria for defining “modular”, and adjustments to the proposed minimum maintenance intervals or replacement restrictions we should consider to account for improved serviceability of modular components.

v. Critical Emission-Related Maintenance for New Technology

Current provisions of 40 CFR 86.094-25(b)(7) outline a process for manufacturers to seek approval for new scheduled maintenance that includes an EPA announcement of the maintenance interval in the Federal Register . Regarding new scheduled maintenance on existing technology, we are proposing not to migrate the provision in 40 CFR 86.094-25(b)(7)(i) for maintenance practices that existed before 1980. Instead, the maintenance demonstration and minimum maintenance interval provisions we are proposing in the new 40 CFR 1036.125(a) would cover the current process for new maintenance on critical emission-related components currently in use.

Regarding scheduled maintenance on new technology, the provision currently in 40 CFR 86.094-25(b)(7)(ii) provides a process for approval of new critical emission-related maintenance associated with new technology. We recognize that new emission control technology may be developed in the future and it is important to retain a public process for approving maintenance associated with new technology. We are proposing to migrate and update 40 CFR 86.094-25(b)(7)(ii) into a new 40 CFR 1036.125(a)(3) for scheduled critical emission-related maintenance associated with new technology. We are proposing to use model year 2020 as the reference point for considering whether technology is new. Manufacturers using new technology would request a recommended maintenance interval, including data to support the need for the maintenance, and demonstrate that the maintenance is likely to occur at the recommended interval using one of the conditions proposed in 40 CFR 1036.125(a)(1). We are also proposing to continue our responsibility to communicate such a decision on maintenance for new technology. As such, we propose to retain EPA's obligation to publish a Federal Register notice based on information manufacturers submit and any other available information to announce that we have established new allowable minimum maintenance intervals.

Manufacturers would also continue to have the option currently specified in 40 CFR 86.094-25(b)(7)(iii) to ask for a hearing if they object to our decision. Hearing procedures are specified in 40 CFR 1036.820 and 40 CFR part 1068, subpart G, including proposed new provisions in 40 CFR part 1068. We request comment on our proposed maintenance provisions for new technology, including our proposal to use model year 2020 to distinguish “new” technology.

vi. Payment for Scheduled Maintenance

The minimum maintenance intervals specified in Table IV-11 would apply for replacement of the listed components and systems. While we are proposing replacement intervals for other components in the catalyst and particulate filtration systems, current maintenance provisions in 40 CFR 86.004-25(b)(4)(iii) state that only adjustment and cleaning are allowed for catalyst beds and particulate filter elements and that replacement is not allowed during the useful life. Current 40 CFR 86.004 25(i) clarifies that these components could be replaced or repaired if manufacturers demonstrate the maintenance will occur and the manufacturer pays for it. We propose to continue to restrict replacement of catalyst beds and particulate filter elements, requiring that manufacturers pay for the repair or replacement of catalyst beds and particulate filter elements, if needed, within the regulatory useful life.

We are proposing to identify these and other components with limited replacement using four criteria based on current provisions that apply for nonroad compression-ignition engines. Our proposed 40 CFR 1036.125(g) states that manufacturers would pay for scheduled maintenance, including parts and labor, if all the following criteria are met:

• Each affected component was not in general use on similar engines before 1980,
• The primary function of each affected component is to reduce emissions,
• The cost of the scheduled maintenance is more than 2 percent of the price of the engine, and
• Failure to perform the maintenance would not significantly degrade the engine's performance.

Scheduled maintenance for the replacement of catalyst beds and particulate filter elements meets the four criteria of 40 CFR 1036.125(g). We estimate that EGR valves, EGR coolers, and RESS also meet the 40 CFR 1036.125(g) criteria and, under this proposal, manufacturers would only be able to schedule replacement of these three components if the manufacturer pays for it. In the HD Omnibus rulemaking, CARB included turbochargers in their list of components “not replaceable” during the regulatory useful life. Under the proposed criteria specified in 40 CFR 1036.125(g), scheduled turbocharger maintenance would not meet all four criteria of the 40 CFR 1036.125(g), since a turbocharger's primary function is not to reduce emissions and an underperforming or failed turbocharger would degrade engine performance. We request comment on including turbochargers as components that should have limited replacement irrespective of the four 40 CFR 1036.125(g) criteria. We also request comment on other components that meet the criteria, or other criteria EPA should consider when determining which components should have limited replacement during the scheduled maintenance approval process.

vii. Source of Parts and Repairs

CAA section 207(c)(3) prohibits manufacturers from requiring maintenance work be completed only by OEM-authorized dealers. We are proposing a new paragraph 40 CFR 1036.125(f) to clarify that manufacturers cannot limit the source of parts and repairs for maintenance. This paragraph would require manufacturers to clearly state in their maintenance instructions that owners can choose any repair shop or person to perform maintenance. Furthermore, the manufacturers cannot specify a particular brand, trade, or corporate name for components or service and cannot deny a warranty claim due to “improper maintenance” based on owners choosing not to use a franchised dealer or service facility or a specific brand of part. The existing and proposed provisions allow manufacturers to specify a particular service facility and brand of parts only if they are providing the service or component to the owner without charge or if the manufacturer convinces EPA during the approval process that the engine will only work properly with the identified service or component.

viii. Maintenance Instructions

Our proposed 40 CFR 1036.125 preserves the requirement that the manufacturer provide written instructions for properly maintaining and using the engine and emission control system. We are proposing a new 40 CFR 1036.125(h) to describe the information that would be required in an owner's manual. The proposed 40 CFR 1036.125(h) generally migrates the existing maintenance instruction provisions specified in 40 CFR 86.010-38(a) through (i) with updates as described in Sections IV.B.3 and IV.C of this preamble. As noted in Section IV.B.3, our serviceability proposal supplements the current service information provisions currently specified in 40 CFR 86.010-38(j). We are not proposing to migrate the service information provisions into part 1036; rather, we would preserve their current location in 40 CFR 86.010-38(j), with updated references to any sections migrated to the new part 1036.

While 40 CFR 1036.120(d) allows manufacturers to deny warranty claims for improper maintenance and use, owners have expressed concern that it is unclear what recordkeeping is needed to document proper maintenance and use. Consistent with the current 40 CFR 86.010-38(a)(2), we propose that manufacturers describe in the owner's manual the documentation they consider appropriate to demonstrate the engine and emission control system are properly maintained (see 40 CFR 1036.125(h)(2)). Manufacturers should be able to identify specific examples of maintenance practices they would consider improper, and to identify their expectations for documenting routine maintenance and repairs related to warranty claims. If a manufacturer requires a maintenance log as part of their process for reviewing warranty claims, we expect the owner's manual would provide an example log that includes the required maintenance tasks and intervals and clearly states that warranty claims require an up-to-date maintenance record. We would be able to review the manufacturers information describing the parameters and documentation for demonstrating proper maintenance before granting certification for an engine family.

ix. Performing Scheduled Maintenance on Test Engines

Current provisions defining the limits on maintenance that can be performed during testing are specified in 40 CFR 86.004-25(e) and (f). We are not migrating those provisions into part 1036; instead, we are proposing that the general provisions currently in 40 CFR 1065, subpart E, would apply for criteria pollutant standards for model year 2027 and later engines.

We are proposing to update 40 CFR 1065.410(c) to clarify that inspections performed during testing include electronic monitoring of engine parameters, such as prognostic systems. Manufacturers that include prognostic systems as part of their engine packages to identify or predict malfunctioning components may use those systems during durability testing and would include any maintenance performed as a result of those systems, consistent with 40 CFR 1065.410(d), in their application for certification. We note that, in order to apply these electronic monitoring systems in testing, the inspection tool ( e.g. , prognostic system) must be available to all customers or accessible at dealerships and other service outlets.

C. Onboard Diagnostics

As used here, the terms “onboard diagnostics” and “OBD” refer to systems of electronic controllers and sensors required by regulation to detect malfunctions of engines and emission controls. EPA's existing OBD regulations for heavy-duty engines are contained in 40 CFR 86.010-18, which were initially promulgated February 24, 2009 (74 FR 8310). EPA's OBD requirements promulgated in 2009 were harmonized with CARB's OBD program then in place. Since 2009, CARB has revised their OBD requirements, while EPA's requirements have not changed. EPA's existing OBD program allows manufacturers to demonstrate how the OBD system they have designed to comply with California OBD requirements for engines used in applications greater than 14,000 pounds also complies with the intent of existing EPA OBD requirements. When applying for EPA 50-state certification, all manufacturers currently seek OBD approval from CARB for OBD systems in engine families and then demonstrate compliance with EPA's OBD regulations through this provision. Currently all heavy-duty manufacturers are certifying to the revised CARB OBD regulations that took effect in 2019.

As part of our effort to evaluate EPA compliance programs, we are proposing to update our OBD regulations both to better address newer diagnostic methods and available technologies and to streamline provisions where possible. These revised regulations are being proposed in 40 CFR 1036.110.

1. Incorporation of California OBD Regulations by Reference

CARB OBD regulations for heavy-duty engines are codified in title 13, California Code of Regulations, sections 1968.2, 1968.5, 1971.1 and 1971.5. These regulations have been updated by CARB several times since EPA initially promulgated HD OBD regulations in 2009. The most recent updates were in October of 2019 and start to phase in with MY 2022. It is possible that CARB could further update their heavy-duty OBD regulations prior to the final rulemaking for this program. In July 2021, CARB proposed changes to their OBD program. These amendments may include adding the use of Unified Diagnostic Services (“UDS”) to address the concern about the limited number of remaining, undefined 2-byte diagnostic trouble codes and the need for additional codes for hybrid vehicles. These amendments may also modify freeze frame requirements, in-use monitoring performance ratio requirements, and expand readiness group lists. As discussed below, our proposal intends to harmonize with the majority of CARB's existing OBD regulations, as appropriate and consistent with the CAA. EPA also seeks comment on harmonizing with any future OBD amendments that may result from this proposal.

In response to the ANPR, EPA received a number of comments supportive of EPA's adoption of the revised CARB OBD program including the 2019 rule amendments. In particular, many commenters were supportive of the new tracking requirements contained in CARB's updated OBD program, known as the Real Emissions Assessment Logging (“REAL”) program to track real-world emissions systems performance of heavy-duty engines. This update requires the collection of onboard data using existing OBD sensors and other vehicle performance parameters, which would allow the assessment of real-world, in-use emission performance relative to laboratory performance beginning in the 2022 model year.

In developing the ANPR, we considered proposing to update the current text in 40 CFR 86.010-18 and migrate it into the new 40 CFR 1036.110. However, given industry's familiarity with the current CARB regulations, we have decided instead to propose incorporating by reference in 40 CFR 1036.110 the existing CARB OBD regulations updated in 2019 as the starting point for our updated OBD regulations. EPA's proposed OBD requirements are closely aligned with CARB's existing requirements with a few exceptions. We are proposing to exclude certain provisions that are not appropriate for a federal program and to include additional elements to improve on the usefulness of OBD systems for users. We are taking comment on whether and to what extent we should harmonize with CARB's next expected update to their OBD regulations, or whether the proposed language in 40 CFR 1036.110(b) is sufficient to accommodate any future divergence in CARB and EPA OBD requirements. EPA anticipates that this language would allow for EPA approval of OBD systems that meet certain parts of updated CARB requirements ( e.g. , updated communication protocols), as long as such provisions meet the intent of EPA OBD requirements.

i. OBD Threshold Requirements

The most essential component of the OBD program is the threshold requirement. Heavy-duty engine emission control components can contribute to an increase in emissions if they malfunction and therefore, they must be monitored by OBD systems. Existing OBD requirements specify how OBD systems must monitor certain components and indicate a fault code prior to when emissions would exceed emission standards by a certain amount, known as an emission threshold. Emission thresholds for these components are generally either an additive value above the exhaust emission standard, or a multiple of the standard. Reductions to emission standards mean that without additional action, OBD thresholds would also be reduced proportionally.

The CARB Omnibus Amendments to the HD OBD regulation include a provision that will not proportionally reduce NO_X and PM OBD threshold requirements that correspond to the new lower emission standards. This means the future numerical values of OBD NO_X and PM thresholds would remain unchanged from today's numerical thresholds as a part of that rulemaking. CARB noted in the Omnibus rule that more time is needed to fully evaluate the capability of HD OBD monitors to accommodate lower thresholds that would correspond to lower emission levels. EPA is proposing to harmonize with this policy and not lower OBD NO_X and PM threshold levels in our proposed OBD regulations at this time. EPA may consider updating threshold requirements in a separate action which may align with a future CARB action. Specifically, we are proposing that heavy-duty compression-ignition engines would be subject to NO_X and PM thresholds of 0.4 g/hp-hr and 0.03 g/hp-hr, respectively, for operation on the FTP and SET duty cycles. For spark ignition engines, we are proposing the following thresholds to align with CARB: 0.30 g/hp-hr for monitors detecting a malfunction before NO_X emissions exceed 1.5 times the applicable standard, 0.35 g/hp-hr for monitors detecting a malfunction before NO_X emissions exceed 1.75 times the applicable standard, and 0.60 g/hp-hr for monitors detecting a malfunction before NO_X emissions exceed 3.0 times the applicable standard. For spark ignition engines, we are also proposing a 0.015 g/hp-hr threshold for PM emissions to align with CARB. EPA is seeking comment on this proposed action, or whether thresholds should be modified as a part of this proposal.

ii. CARB OBD Provisions Revised or Not Included in the Proposed Federal Program

EPA is proposing to adopt the majority of the CARB OBD program. However, we are proposing that some provisions may not be appropriate for the federal regulations. As part of CARB's development of the 2019 OBD program, a number of stakeholders submitted comments to CARB. In developing this proposal, we have reviewed the concerns raised by stakeholders to CARB to help us determine what provisions may not be appropriate in a federal program. In a new 40 CFR 1036.110(b), we are proposing clarifications and changes to the 2019 CARB regulations we are otherwise incorporating by reference, including provisions related to:

1. Providing flexibilities to delay compliance up to three model years for small manufacturers who have not previously certified an engine in California,

2. Allowing good engineering judgment to correlate the CARB OBD standards with EPA OBD standards,

3. Clarifying that engines must comply with OBD requirements throughout EPA's useful life as specified in 40 CFR 1036.104, which may differ from CARB for some model years,

4. Clarifying that the purpose and applicability statements in 13 CCR 1971.1(a) and (b) do not apply,

5. Specifying NO_X and PM threshold requirements,

6. Not requiring the manufacturer self-testing and reporting requirements in 13 CCR 1971.1(i)(2.3) and 1971.1(i)(2.4),

7. Retaining and migrating our existing deficiency policy into proposed 40 CFR 1036.110(d), and specifying that the deficiency provisions in 13 CCR 1971.1(k) do not apply,

8. Requiring additional freeze frame data requirements,

9. Requiring additional data stream parameters for compression- and spark-ignition engines, and

10. Providing flexibilities to reduce redundant demonstration testing requirements for engines certified to CARB OBD requirements.

Manufacturers indicated concern with the existing manufacturer self-testing (“MST”) requirements in 13 CCR 1971.1(i)(2.3 and 2.4). This provision requires manufacturers to obtain vehicles that have reached their full useful life and remove the engine for extensive testing to quantify emission performance and deterioration of the system elements in a manner that allows comparison to deterioration and performance levels achieved with the manufacturer's accelerated aging process. In 2009, when EPA initially promulgated OBD regulations for the heavy-duty industry, we were concerned about the difficulty and expense of removing an in-use engine from a vehicle for engine dynamometer testing, and we did not adopt such a requirement at that time. EPA continues to be concerned that the cost of this testing may be significant and is not warranted for the federal program. Further, we believe that the information CARB gains from this program can be shared with EPA and would help inform us of the ongoing progress manufacturers are making with OBD compliance. Therefore, while we are proposing to exclude this CARB OBD provision from the EPA OBD regulations at this time, we are proposing that manufacturers submit the results of any MST testing performed for CARB to EPA.

EPA requests comments and information on whether there are opportunities for further reducing OBD compliance and certification costs of the federal program through increasing the use of modeling or other calculation-based methods as a part of the certification process which could potentially replace certain testing requirements. Examples could include test-out provisions or testing required for infrequent adjustment factors. CARB's OBD program includes provisions that may allow for certain components to meet specific test-out criteria which would exempt them from monitoring requirements. For example, 13 CCR 1971.1(e)(3.2.6)(B) describes how EGR catalysts would be exempt from monitoring if manufacturers can show that both of the following criteria are satisfied: (1) No malfunction of the EGR catalyst can cause emissions to increase by 15 percent or more of the applicable NMHC, NO_X, CO, or PM standard as measured from an applicable emission test cycle; and (2) no malfunction of the EGR catalyst can cause emissions to exceed the applicable NMHC, NO_X, CO, or PM standard as measured from an applicable emission test cycle. EPA is seeking comment on whether manufacturers could use modeling or other calculation-based methods to determine if such test-out criteria are met.

Another example where the use of modeling or other calculation-based methods could reduce testing requirements is for the calculation of infrequent regeneration adjustment factors for engines equipped with emission controls that experience infrequent regeneration events. These adjustment factors are used to account for emissions from regeneration events when determining compliance with EPA standards. Manufacturers must conduct testing to develop these adjustment factors using the same deteriorated component(s) used to determine if the test-out criteria are being met. EPA is seeking comment on whether it is possible and appropriate to consider modeling- or calculation-based methods to replace certain hardware-based test methods in these or other areas of certification to reduce costs without reducing the functionality of the existing OBD requirements.

EPA is seeking comment on how these or other provisions in the existing or any potential upcoming CARB OBD regulation could be modified to better suit the federal OBD program. It is important to emphasize that by not incorporating certain existing CARB OBD requirements ( e.g. , the in-use engine test program) into our regulations, we are not waiving our authority to require such testing on a case-by-case basis. CAA section 208 gives EPA broad authority to require manufacturers to perform testing not specified in the regulations in such circumstances. Thus, should we determine in the future that such testing is needed, we would retain the authority to require it pursuant to CAA section 208.

EPA is proposing to retain our existing deficiency provisions in 40 CFR 86.010-18(n) and not harmonize with CARB's deficiency provisions in 13 CCR 1971.1(k). In the 2009 OBD rule, EPA stated that having a deficiency provision is important “because it facilitates OBD implementation by allowing for certification of an engine despite having a relatively minor shortfall,” and that while the CARB OBD regulations have a provision to charge fees associated with OBD deficiencies, EPA has “never had and will continue not to have any such fee provisions.” EPA is requesting comment on retaining our existing deficiency requirements in its entirety or if any changes should be made. EPA also seeks comment on how and for what reasons OEMs have utilized CARB's deficiency policy, how this may impact compliance with the new EPA and CARB requirements and how this may be impacted by any future changes in OBD emission thresholds.

CARB's 2019 OBD update to 13 CCR 1971.1 also includes significant changes applicable to hybrid vehicles. We are aware that current OBD requirements necessitate close cooperation between engine and hybrid powertrain system manufacturers for certification, which can present a significant challenge for introducing heavy-duty hybrids into the marketplace. To learn more about this potential challenge, EPA requested input in the ANPR. We learned from commenters that no manufacturers have pursued a certification flexibility that CARB put in place in 2016 through the Innovative Technology Rule (ITR). The ITR provided short-term certification flexibilities, such as allowing hybrid manufacturers to use Engine Manufacturers Diagnostics (EMD), rather than heavy-duty OBD for two to four consecutive model years depending on the all-electric range of the vehicle. We also heard from at least one hybrid manufacturer suggesting that onboard NO_X sensors could be used in lieu of OBD for heavy-duty hybrids. The potential use of onboard sensors to meet some OBD requirements for any heavy-duty vehicle, including hybrids, is discussed in Section IV.C.2.ii below. We continue to be interested in understanding from commenters and request comment on whether and how OBD may present a barrier to the adoption of heavy-duty hybrid systems, and any potential opportunities for EPA to address such barriers. We have prepared a memorandum that further explores these regulatory issues, with a discussion of a range of possible options that we are considering for hybrid systems in heavy-duty specialty vehicles, but which could apply more broadly to all heavy-duty hybrid systems.

Finally, EPA is seeking comment on whether improvements could be made to OBD to monitor inducement conditions. For example, while individual components responsible for inducements currently are monitored ( e.g. , DEF level sensors), there is no requirement that inducements themselves be monitored to ensure a false inducement did not occur or that such events are tracked for remediation. EPA seeks comment on whether OBD systems should monitor the inducement process and detect system malfunctions prior to a failure ( e.g. , for deterioration of the DEF delivery system) to improve emission system performance by providing opportunities for repairs to be made prior to complete failures and by preventing inducements that either should not have occurred or could have been avoided.

iii. Additional OBD Provisions in the Proposed Federal Program

EPA received comments on the ANPR from a wide variety of stakeholders describing difficulties diagnosing problems with and maintaining proper functionality of advanced emission technologies and the important role accessible and robust diagnostics play in this process. The California Air Pollution Control Officers Association and NACAA commented on the need for EPA to develop and maintain a robust OBD program with diagnostic specificity that would ensure OBD continues to accurately detect system failures for lower emission standards and inform the person performing the repair of what the problem is and the cause, so it can be promptly, proficiently and cost-effectively repaired, as well as to facilitate the development of comprehensive enforcement programs. The Pennsylvania Department of Environmental Protection commented that EPA should evaluate how advances in OBD technology could be applied to enhance operations, monitoring and maintenance capabilities of heavy-duty diesel aftertreatment systems and how current and future technologies may use OBD technologies to inform operators and repair technicians as to the in-use efficacy of those systems across multiple duty cycles. ATA commented that ease of diagnostics for emission component failures is a significant concern for their members. NASTC members expressed significant frustration with the inability to use existing diagnostics to understand problems with emission components.

As a part of our effort to update our OBD program and respond to these concerns, EPA is proposing to include additional requirements as well as modify certain CARB OBD requirements to better address newer diagnostic methods and technologies and to ensure that OBD can be used to properly diagnose and maintain emission control systems to avoid increased real-world emissions. EPA intends to continue to accept CARB OBD approval where a manufacturer can demonstrate that the CARB program meets the intent of EPA OBD requirements (see section IV.C.2.i.b. for further discussion), and manufacturers would submit documentation as specified in proposed 40 CFR 1036.110(c)(5) to show that they meet the additional requirements proposed here.

In this section we describe the following proposed additional EPA certification requirements in 40 CFR 1036.110 for OBD systems:

1. Health monitors for the SCR, DPF, and EGR systems

2. Display health monitor and inducement-related information in the cab

3. Diagnostic testing to measure the effectiveness of DEF dosing must be made available for use with either a generic scan tool or an equivalent alternative method

Enhanced OBD systems that provide more information and value to the operator can play an important role in ensuring expected in-use emission reductions are achieved long-term. For example, in comments to the ANPR, CARB stated that their test programs have identified numerous heavy-duty vehicles with mileages within their applicable regulatory useful life periods, but beyond their warranty periods, that had NO_X emission levels significantly above the applicable certification standards. CARB also stated that some stakeholders such as fleet owners, retrofit installers, and equipment operators have communicated to CARB that they are experiencing significant vehicle downtime due to parts failures.

Increasing the transparency and usefulness of OBD systems can help to improve maintenance and repair experiences and also serve as a mechanism to reduce owner frustration (which otherwise could provide motivation to tamper). EPA is specifically proposing to improve the robustness and usefulness of OBD systems by including emission system health monitors, increasing the number of publicly available data parameters, increasing the freeze frame data, and enabling certain self-testing capabilities for owners. These changes will benefit the environment by helping to reduce malfunctioning emission systems in-use through access to additional data that may be useful for service technicians, state and local inspection and maintenance operations, and owners. These capabilities are also important to enable owners to avoid potential inducement conditions that can result from certain component failures.

a. Emissions Systems Health Monitor

The purpose of OBD is to reduce motor vehicle and motor vehicle engine emissions by monitoring the systems in-use, detecting malfunctions, informing the operator, and assisting with diagnosis of emission system problems. One concept EPA is proposing to incorporate into our updated OBD regulations is the development of “health monitors” for specific emission control technologies on CI engines to provide vehicle owners information on the overall health of important emissions systems at a given point in time. While OBD systems are highly proficient in monitoring emission systems and components, the historic purpose of OBD has been to monitor systems but only notify operators generically ( e.g., through the Malfunction Indicator Light or “MIL”) once there is a failure or malfunction, rather than to use monitored data to proactively provide the operator with information on the functionality and status of such systems. However, existing OBD monitors and data parameters could also be used in a different way to generate aftertreatment health monitors. This could be accomplished by evaluating data indicating how much a system has been used or how close a system is to exceeding an OBD threshold. While most large fleets have already begun to use similar measures by using big data and telematics to implement predictive maintenance, this concept is different in that it would be focused on using a particular vehicle's data to evaluate system status as opposed to using data from thousands of trucks to predict system status. Predictive maintenance relies on analytics that examine existing data to identify potential risks of failure on particular trucks or components prior to the failures occurring in the field. Predictive maintenance can enable operators to replace components later than when utilizing a traditional preventative maintenance approach and can essentially increase the service life of certain emission system components, prevent breakdowns, and reduce total operating costs. Predictive maintenance could also result in components being changed more frequently to avoid or reduce breakdowns and downtime, thereby also reducing total operating costs. An emissions system health monitor, while not as comprehensive of a tool as predictive maintenance, could provide similar types of benefits resulting in more uptime for emission control systems. Health monitors could also provide critical insight on the status of a vehicle's emissions systems for buyers considering purchasing used trucks. EPA is proposing that the health monitors' status would need to be made available on the dash or other display for access to the data without the use of a scan tool. The purpose of the health monitor is not to guarantee the performance of an emissions system in the future, but instead to provide status information on the functioning of the relevant system at the moment in time. In addition, such a monitor could be used to warn users of potential upstream failures that can cause damage to aftertreatment components resulting in expensive repairs. EPA worked with Environment and Climate Change Canada (“ECCC”) to develop this concept. Using an emissions system health monitor to improve and make more efficient heavy-duty engine and vehicle maintenance practices could provide environmental benefits by helping to sustain system performance long-term.

In discussions with ECCC about how to develop a health monitor concept, they suggested that a single value representing the performance of the vehicle's emission system as a whole would be less effective than two or three individual “health monitors”, and EPA agrees. EPA is proposing, and seeking comment on the benefits of, specific methods for CI engines to inform a vehicle operator of the general health of the DPF, SCR, and EGR systems. There are two main approaches EPA could use to achieve this goal: (1) A broad requirement that leaves the identification and implementation of the specific methodologies up to each manufacturer, or (2) a specific requirement that prescribes the methodologies to be used by all manufacturers. EPA is proposing the first alternative, and seeks comment on the second alternative, or any other alternative that commenters believe would be more beneficial or less costly and that would still provide benefits to the owner and resulting environmental benefits from better performing emissions controls systems. Under any approach, we are interested in emissions system health monitors that better enable owners to understand emission system functionality, help avoid potential breakdowns, and reduce incentives to tamper with emission control systems as a result of experiencing unplanned and catastrophic emission system failures. A prescriptive approach may be more useful in that it would provide consistency between manufacturers which could result in more useful and stable data for users, however, a broad requirement that allows manufacturers to better capitalize on their existing OBD system design may also achieve the goals of this health monitor proposal. This proposal focuses on leveraging existing OBD requirements in new ways to develop health monitors for DPF, SCR, and EGR systems to avoid costs that could be associated with an entirely new monitoring requirement. EPA seeks comment on whether additional monitors could be developed utilizing existing OBD requirements which can further help prevent downtime, such as additional upstream health indicators ( e.g., preventing excessive internal oil leaks) to proactively prevent damage to expensive aftertreatment components.

(1) Proposed DPF Health Monitor

For the DPF system, EPA has identified essential information that users should have access to for ensuring that proper maintenance and use can occur. Having continuous access to DPF health information can provide important insight on DPF system status. EPA is proposing that users have access to the following information available for display in the cab, which together would form the DPF health monitor: (1) A value that indicates general system wear, for example a counter for the total number of passive and active regeneration (“regen”) events that have taken place on the existing DPF, (2) a value that indicates the average active and passive regen frequency and a method for operators to track changes in these values, (3) a value estimating (in miles or hours) when the DPF needs to be cleaned to remove accumulated ash, and (4) notification when active regens have been disabled by the system (even temporarily) if accompanied by a derate, as well as the reason it was disabled. While not specifically a part of the DPF health monitor, EPA is proposing additional DPF maintenance information be made available to users to improve serviceability experiences, see section IV.B.3.ii. for more discussion on these proposed requirements.

Providing users with a general indicator of system wear can help users make informed maintenance decisions. EPA would expect that a manufacturer would allow this monitor to be reset if a DPF is replaced. Manufacturers could in part utilize work that may be done to meet CARB OBD requirements to implement this proposal. For example, the 2019 CARB OBD program that we are proposing to harmonize with includes a provision for MY 2024 that requires a lifetime counter of DPF regens (see 13 CCR 1971.1(h)(5.8.2)). EPA is seeking comment on the use of CARB's required lifetime counter to meet this proposed requirement, or what alternative information manufacturers could use to meet this requirement and whether this information should be standardized.

Providing users with an indication of the total average regen frequency (active and passive) and with a method that could be used to detect recent changes in system function can allow users to familiarize themselves with proper system operation. For example, this could be achieved by displaying the average regen frequency per a fixed number of miles or hours and providing a resettable counter to show the most recent average regen frequency. Such a feature would enable owners to monitor the number of regens occurring over a particular route to detect changes ( e.g., a significant increase in the number of regeneration events) which could inform them of the need to address failures upstream of the DPF, clean the DPF, or service the DPF system. In particular, EPA seeks to alert operators to potential conditions that could indicate an upstream problem ( e.g., an oil leak) that can damage sensitive aftertreatment components prior to a catastrophic failure or result in the need for costly repairs to aftertreatment systems. Manufacturers may be able to utilize existing work already being done to meet the frequent regeneration requirements in 13 CCR 1971.1(e)(8.2.2) to inform owners when regen frequency exceeds a certain level that may indicate an upstream issue. As discussed earlier, EPA is proposing that the health monitors' status would need to be made available on the dash or other display for access to the data without the use of a scan tool. EPA would expect that operators would be able to access this information on demand, and that manufacturers would not have the health monitor tied to the MIL to avoid any confusion. EPA is seeking comment on whether this component of the DPF health monitor is important enough to require that it be communicated when the frequency of regens reaches a particular level that may indicate the need for inspection and possibly repair, what this level would be, and what such a warning system should look like.

Having access to information that indicates an estimate of when the DPF needs to be cleaned would allow operators to plan ahead for critical maintenance and reduce downtime. We are not proposing a specific method manufacturers would use to generate the estimated time to perform such a cleaning, rather we would leave it to manufacturers to determine the best method of implementation.

Finally, providing operators with notification of when active regens have been disabled by the system (even temporarily) as well as the reason it was disabled would provide benefits to operators and repair technicians. Manufacturers generally implement severe derates when DPF system faults occur that prevent active regens from occurring. Providing owners with information on the cause of a DPF-related derate would reduce frustration and may reduce downtime by allowing repairs to be made more quickly, increasing in-use emission system performance.

EPA is seeking comment on how manufacturers could lessen the effects of duty cycle related regens frequency variability in the health monitor ( e.g., vehicles that operate more at lower speeds would likely experience more active regens than those that operate at higher steady-state speeds), through normalizing the reported data or focusing on specific regions of operation where regens occur with more regularity. For example, this DPF health monitor parameter could include only passive regens that occur during certain vehicle operation, such as operation that occurs in OBD REAL Bin 14. EPA is seeking comment on whether the DPF health monitor should provide this information on demand, and if it should also notify users of potential concerns.

(2) Proposed SCR Health Monitor

For the SCR system, EPA has identified essential information that users should have access to for ensuring that proper preventive maintenance occurs. EPA is proposing that the SCR health monitors' status would need to be made available on the dash or other display for access to the data without the use of a scan tool. Having access to SCR health information on demand can provide important insight on SCR system status and help operators prevent inducements from occurring. EPA is proposing that users have access to the following information for the SCR health monitor: (1) Indicator of average DEF consumption and a method for operators to track changes in this value, (2) warnings before blockages in the DEF line or dosing valve actually occur and an inducement would be triggered, and (3) information on when DEF dosing has been disabled by the system (even temporarily) if accompanied by a derate as well as the reason it was disabled. EPA is not proposing specific methods manufacturers would use to meet these requirements and would be leaving it up to manufacturers to develop the most appropriate method based on their product designs. We are taking comment on this approach, or if instead we should specify the way the SCR health monitor should be implemented, which would ensure consistency across the fleet.

Providing users with an indication of average DEF consumption and with a method that could be used to detect recent changes in that value can allow users to familiarize themselves with proper system operation. This could be achieved for example by manufacturers providing the lifetime average DEF used per gallon of fuel and a recent or resettable counter to show the most recent average DEF consumption value. Such a feature would enable owners to develop a high-level understanding of proper SCR function and operation, can alert the operator to changes that may indicate a problem before there is a failure resulting in a breakdown and corresponding downtime, and enable owners to monitor the data over a particular route (or after a particular repair) to detect system changes (or evaluate the effectiveness of a recent repair).

EPA is seeking comment on how manufacturers could lessen the effects of duty cycle related DEF consumption variability in the health monitor, through normalizing the reported data or focusing on specific regions of operation where DEF consumption should be more stable. For example, this SCR health monitor parameter could include provide average DEF consumption that occurs during certain vehicle operations, such as operation that occurs in OBD REAL Bin 14.

The SCR health monitor proposal also includes a requirement for manufacturers to provide information to the operator regarding potential plugging of the DEF line or dosing valve prior to a blockage actually occurring. Manufacturers have likely developed strategies to monitor such blockages in response to EPA's existing inducement guidance. DEF can crystallize over time and build up in SCR components such as the injector, which in some cases could also result in a false inducement being triggered for conditions that appear to be caused by tampering, which this health monitor can help prevent. Further, it is critical to ensuring that DEF restrictions are promptly addressed to maintain proper SCR system function. Finally, EPA is proposing that the health monitor provide information on when DEF dosing has been disabled by the system (even temporarily) as well as the reason it was disabled if accompanied by a derate. Having access to this information is critical to ensuring operators can perform maintenance timely, and potentially prior to a vehicle going into inducement. EPA is seeking comment on whether the SCR health monitor should provide this information on demand, and if it should also notify users of potential concerns.

Finally, EPA is seeking comment on alternative methods to develop a health monitor for SCR systems, for example including one that would use DEF dosing trim values ( i.e., DEF dosing rates at particular operating points such as within NTE operating zones or REAL bins) and compare the dosing rate that is occurring in real-time to what the dosing rate was when the vehicle was new. The idea is that as components wear and SCR performance deteriorates, the system may compensate by increasing the DEF dosing rate at a particular operating point; using the information contained in the engine controller software could help alert operators to such changes and allow them to perform repairs or maintenance prior to the vehicle experiencing a catastrophic failure. This method, especially if combined with ammonia slip information, could offer a better indication of system performance.

(3) Proposed EGR Health Monitor

For the EGR system, EPA has identified essential information that users should have access to for ensuing proper maintenance and use can occur. In particular, we expect access to information indicating EGR valve coking or EGR cooler failure, which are the two main failure conditions, may avoid devastating impacts on downstream aftertreatment components. We are proposing to require manufacturers to provide an indication of EGR valve health. For example, they could use existing OBD signals to provide an indication of the health of an EGR valve by looking at the difference between commanded and actual EGR valve position to indicate valve coking. The intent of this health monitor is to enable operators to understand when the EGR valve is becoming plugged and allow them to perform preventative maintenance prior to a catastrophic failure.

In addition, EPA is proposing a health monitor for the EGR cooler. Manufacturers could in part utilize work already being done to meet existing CARB requirements in 13 CCR 1971.1(e) for EGR cooler performance monitoring to satisfy this requirement. These requirements specify that manufacturers design their system to monitor the cooler system for insufficient cooling malfunctions, including the individual electronic components ( e.g., actuators, valves, sensors). The OBD system must detect a malfunction of the EGR cooler system prior to a reduction from the manufacturer's specified cooling performance that would cause an engine's NMHC, CO, or NO_X emissions to exceed 2.0 times any of the applicable standards or the engine's PM emissions to exceed the applicable standard plus 0.02 g/hp-hr. EPA is seeking comment on these or other strategies that can help inform operators of the functionality of the EGR system to help prevent breakdowns due to EGR system failures, including whether or how to monitor for EGR cooler leaks or plugging, such as through the use of pressure or temperature sensors, and whether today's engines are equipped with sensors in the EGR system that could be used for this purpose. We are also seeking comment on whether fault codes related to incidents of engine derate due to EGR-related failures should be displayed in the cab as a part of this health monitor, similar to what is being proposed for SCR and DPF-related derate issues.

b. Expanded List of Public OBD Parameters

In another area for improvement in the OBD program, EPA proposes to harmonize with the revised list of data parameters CARB has developed for MY 2024 through our incorporation by reference of CARB's revised OBD regulations and to further expand the list of OBD parameters that manufacturers are required to make publicly available. 13 CCR 1971.1(4.2) data stream requirements state that the listed signals be made available on demand through the “standardized data link connector” (OBD port) in accordance with J1979/J1939 specifications. The requirements also specify that the actual signal value must be used, the default or limp home value cannot be used. Until MY 2024, CARB regulations require a list of 91 signals that must be made publicly available, of which approximately ten are related to aftertreatment and primarily include measures of the pressure and temperature of the DPF. CARB updated these requirements in 2019 such that additional aftertreatment-related signals will be added in MY 2022 and MY 2024. EPA is proposing to adopt CARB's parameter list through our incorporation by reference of their updated 2019 OBD regulations, to add signals to the list, and to specifically require the addition of all parameters related to fault conditions that trigger vehicle inducement to be made readily available using generic scan tools if the engine is so equipped (see Section IV.D for more discussion on inducements). EPA would expect that each of these additional requirements would need to be addressed even where manufacturers relied in part on a CARB OBD approval to meet the intent of our proposed OBD regulations. The purpose of including additional parameters is to make it easier to identify malfunctions of critical aftertreatment related components, especially where failure of such components would trigger an inducement. In addition, the proposed additional information can make the repairs themselves easier by allowing for immediate access to fault codes, which could alleviate the long wait times associated with specialized emission repair facilities or where facilities are not available when an inducement occurs (such as on the weekend or in a remote location). In response to the ANPR, EPA received comments supportive of such changes, for example from the National Tribal Air Association (“NTAA”) who noted that service information and tools should be made easily available and affordable for individual owners to diagnose and fix their own vehicles, which can be especially important for small businesses, Tribes, and those in rural areas with less ready access to original equipment manufacturer dealer networks.

We are proposing a general requirement to make such parameters available if they are used as the basis for an inducement response that interferes with the operation of the engine or vehicle. For example, if the failure of an open-circuit check for a DEF quality sensor leads to an engine inducement, the owner/operator would be able to identify this fault condition using a generic scan tool. This proposal should be enabled in part by a change to the comprehensive component monitoring requirements in CARB's 2019 OBD regulations. CARB now specifies that for MY 2024 and later, comprehensive component monitoring must include any electronic powertrain component/system that either provides input to (directly or indirectly) or receives commands from an on-board computer or smart device, which is also used as an input to an inducement strategy or other engine derate (see 13 CCR 1971.1(g)(3.1.1)). We are also proposing some new parameters for HD SI engines, as mentioned in Section III.D.2. We are proposing that manufacturers make additional parameters available for all engines so equipped, including:

• For Compression Ignition engines:

○ Inlet DOC and Outlet DOC pressure and temperature

○ DPF Filter Soot Load (for all installed DPFs)

○ DPF Filter Ash Load (for all installed DPFs)

○ Engine Exhaust Gas Recirculation Differential Pressure

○ DEF quality

○ Parking Brake, Neutral Switch, Brake Switch, and Clutch Switch Status

○ Aftertreatment Dosing Quantity Commanded and Actual

○ Wastegate Control Solenoid Output

○ Wastegate Position Commanded

○ DEF Tank Temperature

○ Injection Control Pressure Commanded and Actual

○ DEF System Pressure

○ DEF Pump Commanded Percentage

○ DEF Coolant Control Valve Control Position Commanded and Actual

○ DEF Line Heater Control Outputs

• For Spark Ignition Engines:

○ A/F Enrichment Enable flags: Throttle based, Load based, Catalyst protection based

○ Percent of time not in stoichiometric operation (including per trip, and since new)

○ Catalyst or component temperature parameters (measured and modeled, if applicable) specifically used for thermal protection control strategies as proposed in Section III.D.2.

EPA is seeking comment on whether any additional signals should be included in this list to help ensure in-use emission benefits occur as expected, and whether any other signals should be included such as any signals related to maintenance derates (outside of inducements). Although CARB currently requires a list of signals that must be made public, EPA encountered difficulty accessing many of these signals in recent testing on in-use trucks. EPA, working closely with Environment and Climate Change Canada, used a number of generic scan tools on a variety of vehicle makes and models and were unable to see all of the publicly required data. While this could indicate a problem with a specific generic scan tool design, none of the scan tools from a range of price points was able to display the complete set of signals; some tools read less than a third of the required signals. Some parameters read “No Response” or “Not Available” or were missing a signal in its entirety. This situation can cause frustration for owners who own generic scan tools and are unable to access any required data when trying to repair vehicles. EPA requests comment on operator experiences with obtaining data using generic scan tools from trucks in-use.

c. Expanding Freeze Frame Data Parameters

One of the more useful features in the CARB OBD program for diagnosing and repairing emissions components is the requirement for “freeze frame” data to be stored by the system. To comply with this requirement, manufacturers must capture and store certain data parameters ( e.g., vehicle operating conditions such as the NO_X sensor output reading) within 10 seconds of the system detecting a malfunction. The purpose of storing this data is in part to record the likely area of malfunction. CARB has identified a list of approximately 63 parameters that must be captured in the freeze frame data for gasoline engines and 69 parameters for diesel engines. Currently, the freeze frame data does not include additional signals for aftertreatment systems. While existing CARB freeze frame data requirements include some DPF-related parameters ( e.g., inlet and outlet pressure and temperature), there is essentially no SCR information, which EPA believes is essential for proper maintenance. We are therefore proposing that EPA's updated OBD requirements include the additional parameters proposed in section IV.C(1)(ii)(b) of this preamble and those included in the following section of CARB's regulations sections 13 CCR 1971.1(h)(4.2.1)(D), 1971.1(h)(4.2.2)(H), 1971.1(h)(4.2.3)(F), 1971.1(h)(4.2.3)(G), 1971.1(h)(4.2.2)(I). We welcome comment on this proposal, including whether additional data parameters should be included in the freeze frame data to enable those diagnosing and repairing vehicles to more effectively identify the source of the malfunction and increase the usefulness of freeze frame data, especially for conditions that result in inducement.

d. System Commanded Tests To Facilitate Inducement-Related Diagnoses and Repairs

Today's vehicle control systems have built-in tests that can be used to command components to perform a particular function in order to confirm that they are working properly. An equally important element of an effective OBD program is ensuring owners have the ability to run certain engine or vehicle tests and view the results, especially where they can be used by owners in diagnosing and repairing problems that may result in inducement. If, for example, the problem was caused by a faulty DEF pump, this type of repair likely does not require specialized training to complete but is difficult to detect without access to such a test. More immediate diagnosis and repair of faulty components such as this would result in reduced costs for owners and increased long-term environmental benefits through improved emission control function.

Today, vehicle software scan tools can be designed to command a DEF pump to operate, which allows a person diagnosing a DEF injection issue to measure how much DEF is pumped during a certain time interval and compare this amount to the specifications to determine whether or not the pump and injector are functioning properly. Performing the test would allow diagnosis of the vehicle and a quick determination of whether the DEF pump is working, the DEF injector is not faulty, there are no wiring-related issues, and DEF is being sprayed properly (both in terms of amount and spray pattern). Due to the importance of the DEF pump in maintaining full functionality of a vehicle ( i.e., avoiding inducement), EPA is proposing that the DEF dosing test be made available for use with either a generic scan tool (be made available on demand through the OBD port in accordance with J1979/J1939 specifications) or an alternative method ( e.g., an option commanded through a vehicle system menu).

Another important test that is used today is an SCR performance test that some OEMs offer through their proprietary scan tools. This type of test causes the diagnostic system to run the engine through a specific operating cycle to check certain SCR parameters, providing a pass/fail result and indicating what potential problems may exist. In particular, this test allows for a repeatable method to be used to compare a known set of engine operating parameters and SCR performance specifications to verify that SCR performance is as-expected and to narrow the scope of any existing problems that need to be fixed. There are currently non-OEM scan tools that also can conduct the same test, but the engine's diagnostic system may not allow the generic scan tool to access the pass/fail results. The results of this test could be especially helpful for users or technicians, may help avoid unexpected breakdowns, and may improve in-use emissions. Running an SCR performance test can enable the owner or technician to monitor system parameters during the test ( e.g., by watching SCR inlet and outlet temperatures during a particular operating cycle) to evaluate if certain components are functioning properly during the test and may reduce the need for regens to be run instead, which can reduce wear on the DPF system. We are requesting comment on whether EPA should make SCR performance tests available via generic scan tool or other on-vehicle method. EPA is also requesting comment on the need to make other self-tests accessible with generic scan tools to improve in-use emission systems maintenance and performance, for example being able to command that the evaporative system on SI engines be sealed to allow for leak testing or including the ability to perform manual regens for DPF systems.

2. Other OBD Provisions

In addition to our proposal to update our OBD regulations by incorporating much of the CARB OBD program by reference, we are also requesting comment on other improvements to our OBD program. The improvements would be intended to make the program more effective at improving maintenance of in-use engines and vehicles, as well as reducing the compliance burdens for manufacturers. We welcome comments suggesting other ways to improve our OBD program.

i. OBD Provisions From the Recent HD Technical Amendment Rule

EPA recently revised our OBD regulations to harmonize with certain CARB requirements in our HD Technical Amendments (HDTA) rulemaking (86 FR 34340, June 29, 2021). This rule finalized four updated OBD provisions including: (1) Revising the misfire threshold, (2) adopting updated misfire flexibilities, (3) revising our in-use minimum ratios, and (4) allowing the use of CARB OBD reporting templates for EPA OBD requirements. EPA did not take final action at that time on two proposed revisions related to OBD demonstration testing and carry-over of OBD certification. The following sections summarize the revisions previously proposed and the concerns expressed in comments.

a. Demonstration Testing Requirements

One of the provisions EPA did not take final action on in the HDTA rulemaking was related to determining the number of engines required to undergo demonstration testing. The existing requirements of 40 CFR 86.010-18(l) and 13 CCR 1971.1(l) specify the number of test engines for which a manufacturer must submit monitoring system demonstration emissions data. Specifically, a manufacturer certifying one to five engine families in a given model year must provide emissions test data for a single test engine from one engine rating, a manufacturer certifying six to ten engine families in a given model year must provide emissions test data for a single test engine from two different engine ratings, and a manufacturer certifying eleven or more engine families in a given model year must provide emissions test data for a single test engine from three different engine ratings.

The HDTA proposed rulemaking (85 FR 28152, May 12, 2020) proposed to allow CARB certified configurations to not count as separate engine families for the purposes of determining OEM demonstration testing requirements for EPA OBD approval. EPA received adverse comment on this proposal stating that it was inconsistent for EPA to not include CARB-only families when determining demonstration testing requirements for 49-state EPA families, but to accept demonstration test data from CARB-only families to meet 49-state EPA certification. There were additional concerns that the proposal did not include the criteria that EPA would use to approve or deny the request to not count certain families, and that this proposal applied to “special families” which were not defined by EPA. In the HDTA final rulemaking, EPA explained that this provision required additional consideration and did not take final action on it at that time.

We stated in the HDTA final rulemaking that we intended to review this issue as a part of the HD 2027 proposal. EPA recently issued guidance for certain cases, where an OBD system designed to comply with California OBD requirements is being used in both a CARB proposed family and a proposed EPA-only family and the two families are also identical in all aspects material to expected emission characteristics. EPA anticipates that a manufacturer would be able to demonstrate to EPA that the intent of 40 CFR 86.010-18(l) is met for the EPA-only family by providing proof that CARB has determined the monitoring system demonstration requirements for the corresponding CARB proposed family have been met. We are proposing to codify this as a provision in 40 CFR 1036.110(b)(11). We are requesting comment on this provision, including whether additional restrictions should be included to ensure engine families are appropriately counted. EPA is also seeking comment on allowing a similar provision for cases where equivalent engine families differ only in terms of inducement strategies (see section IV.D.6 for further discussion). Finally, EPA is seeking comment on whether we should include revisions beyond those proposed to address this situation.

b. Use of CARB OBD Approval for EPA OBD Certification

EPA did not take final action on the proposed reordering of 40 CFR 86.010-18(a)(5) in the HDTA final rulemaking. These existing EPA OBD regulations allow manufacturers seeking an EPA certificate of conformity to comply with the federal OBD requirements by demonstrating to EPA how the OBD system they have designed to comply with California OBD requirements also meets the intent behind federal OBD requirements, as long as the manufacturer complies with certain certification documentation requirements. EPA has implemented these requirements by allowing a manufacturer to submit an OBD approval letter from CARB for the equivalent engine family where a manufacturer can demonstrate that the CARB OBD program has met the intent of the EPA OBD program. In other words, EPA has interpreted these requirements to allow OBD approval from CARB to be submitted to EPA for approval.

We are proposing to migrate the language from 40 CFR 86.010-18(a)(5) to 40 CFR 1036.110(a) to allow manufacturers to continue to use a CARB OBD approval letter to demonstrate compliance with federal OBD regulations for an equivalent engine family where manufacturers can demonstrate that the CARB OBD program has met the intent of the EPA OBD program. In the case where a manufacturer chooses not to include information showing compliance with additional EPA OBD requirements in their CARB certification package ( e.g., not including the additional EPA data parameters in their CARB certification documentation), EPA would expect manufacturers to provide separate documentation along with the CARB OBD approval letter to show they have met all EPA OBD requirements. This process would also apply in the case where CARB has further modified their OBD requirements such that they are different from but meet the intent of existing EPA OBD requirements. For example, if CARB finalizes the use of a different communication protocol than EPA's requirements call for, as long as it meets the intent of EPA's communication protocol requirements ( e.g., can still be used with a generic scan tool to read certain parameters), the proposed process would apply. EPA expects manufacturers to submit all documentation as is currently required by 40 CFR 86.010-18(m)(3), detailing how the system meets the intent of EPA OBD requirements, why they have chosen the system design, and information on any system deficiencies. As a part of this update to EPA OBD regulations, we are clarifying in 40 CFR 1036.110(c)(4) that we can request that manufacturers send us information needed for us to evaluate how they meet the intent of our OBD program using this pathway. This would most often mean sending EPA a copy of documents submitted to CARB during the certification process.

c. Potential Use of the J1979-2 Communications Protocol

In a February 2020 workshop, CARB indicated their intent to propose allowing the use of Unified Diagnostic Services (“UDS”) through the SAE J1979-2 communications protocol for heavy-duty OBD with an optional implementation as early as MY 2022. CARB stated that engine manufacturers are concerned about the limited number of remaining undefined 2-byte diagnostic trouble codes (“DTC”) and the need for additional DTCs for hybrid vehicles. J1979-2 provides 3-byte DTCs, significantly increasing the number of DTCs that can be defined. In addition, this change would provide additional features for data access that improve the usefulness of generic scan tools to repair vehicles.

Section IV.C.1. of this preamble asks for comment on whether EPA should harmonize with any updated CARB OBD amendments finalized prior to the issuing of this final rulemaking; however, it is not clear if CARB's amendment including UDS would be finalized in time for EPA to include it in this final rule. We will monitor the development of the CARB OBD update and are seeking comment on whether we should finalize similar provisions if CARB does not finalize their update before we complete this final rule. CARB is expected to allow the optional use of the J1979-2 protocol as soon as MY 2023. If manufacturers want to certify their engine families for nationwide use, we would need to establish a process for reviewing and approving manufacturers' requests to comply using the alternative communications protocol. While we support adoption of J1979-2 and are clarifying and proposing pathways to accommodate its use, we are seeking comment on potential challenges associated with this change.

While EPA believes our existing requirements in 40 CFR 86.010-18(a)(5) allow us to accept OBD systems using J1979-2 that have been approved by CARB, there may be additional considerations prior to the finalization of this rule for OEMs that want to obtain a 49-state certificate for engines that do not have CARB OBD approval. For model years prior to MY 2027, since our proposed OBD revisions would take effect in MY 2027 if finalized, EPA is proposing to include interim provisions in 40 CFR 1036.150(v) to allow the use of J1979-2 for manufacturers seeking EPA OBD approval. Finally, once EPA's proposed updated OBD requirements would be in effect for MY 2027, we expect to be able to allow the use of J1979-2 based on the proposed language in 40 CFR 1036.110(b). We are seeking comment on these pathways to approval and on whether any additional changes need to be made to our existing or proposed OBD requirements to accommodate the use of J1979-2.

While there are expected environmental benefits associated with the use of this updated protocol, we are seeking comment on whether the use of this alternative protocol could have negative impacts on our existing OBD program. In addition to potential impacts on EPA's OBD program, EPA is seeking comment on any potential impacts this change could have on our service information requirements (see Section IV.B.3.ii. for more background on these provisions). CAA section 202(m)(4)(C) requires that the output of the data from the emission control diagnostic system through such connectors shall be usable without the need for any unique decoding information or device, and it is not expected that the use of J1979-2 would conflict with this requirement. Further, CAA section 202(m)(5) requires manufacturers to provide promptly to any person engaged in the repairing or servicing of motor vehicles or motor vehicle engines, and the Administrator for use by any such persons, with any and all information needed to make use of the emission control diagnostics system prescribed under this subsection and such other information including instructions for making emission related diagnosis and repairs. Manufacturers who choose to voluntarily use J1979-2 as early as MY 2022 would need to provide access to systems using this alternative protocol at that time and meet all of the relevant requirements in 40 CFR 86.010-18.

EPA believes that the software and hardware changes needed to accommodate J1979-2 are minimal, and that these changes would not impact an OEM's ability to make vehicle data available at a fair and reasonable cost. We seek comment on how tool vendors would be affected, whether they would be able to support the new services and data available in J1979-2, and if there are any concerns tool manufacturers have regarding access to vehicle data at a fair and reasonable cost.

While the move to UDS has been discussed by OEMs in the past with CARB, a proposal was expected to be released last year, but is now expected this year, and while SAE is working on a new standard, J1978-2 to specify the scan tool requirements to interface with J1979-2, this standard is not yet available. EPA is seeking comment on the impact to generic scan tool manufacturers of the timing of the voluntary allowance for the use of J1979-2 in MY 2023 and whether scan tool manufacturers can provide updated tools for use to diagnose and repair vehicles as well as for inspection and maintenance facilities in time for MY 2023, or if this protocol should not be allowed for use until a later model year and if so what the appropriate timing is. Specifically, EPA is seeking comment on the following issues related to generic scan tools:

• Will vendors be able to meet the MY 2023 timeframe?
• Can existing tools be updated to accommodate the new protocol or do new scan tools need to be developed to utilize J1979-2?
• Will any additional hardware changes be required to accommodate J1979-2?
• Do tool vendors expect the price of tools that can utilize J1979-2 to be comparable to tools that utilize J1979?
• Do state inspection and maintenance facilities require additional time to be able to modify or update equipment to handle J1979-2?
• Will generic scan tools be able to read both J1979-2 and J1979 or will separate tools be required?
• Will generic scan tool functionality be the same or better with the implementation of J1979-2?
• Will users require specialized training to use J1979-2 tools?
• Is development going to be delayed until the adoption of SAE J1978-2?

ii. Use of Tailpipe Emission Sensors

EPA is seeking comment on whether and how to allow manufacturers to use onboard emission sensors to help reduce test burden associated with OBD certification. In particular, EPA would like comment on ways to reduce test cell time associated with component threshold testing, such as ways to use NO_X sensor data instead of test cycle NO_X measurements (provided those sensors meet the proper specifications). There are further complications for testing outside of a test cell to demonstrate compliance that need careful consideration (as it is assumed that testing that relies on onboard NO_X sensors would happen outside of a test cell), including:

• What alternative testing methods are reasonable and would provide assurances that they are creating robust diagnostic systems?
• For what operating conditions and over what time frame should this testing occur?

• What NO_X values should be considered ( e.g., average NO_X over a certain period of time, or for a particular set of operating conditions?)

• What ambient and vehicle operating conditions should be considered?
• How can this methodology ensure repeatable results?
• How would EPA verify this methodology for compliance assurance?

This type of strategy could potentially reduce compliance costs because it would reduce the amount of emission testing manufacturers need to perform in a test cell during OBD development. We request comment on this and other aspects of the OBD program that could be improved through the use of emissions sensors. EPA is also seeking comment on alternative methods to use onboard emission sensors that could be used to generate and provide real-world data that may enable improved diagnostics, assess the function of emissions critical components and assess the implementation of dynamic AECD inputs. Such a program could be voluntary and provide additional data that could be used in the future to analyze whether changes to the OBD program should be made to improve compliance demonstrations and reduce test cell burden.

3. Cost Impacts

Heavy-duty engine manufacturers currently certify their engines to meet CARB's OBD regulations before obtaining EPA certification for a 50-state OBD approval. We anticipate most manufacturers would continue to certify with CARB and that they would certify to CARB's 2019 updated OBD regulations well in advance of the EPA program taking effect; therefore, we anticipate the incorporation by reference of CARB's 2019 OBD requirements would not result in any additional costs. EPA does not believe the additional OBD requirements described here would result in any significant costs, as there are no requirements for new monitors, new data parameters, new hardware, or new testing included in this rule. However, EPA has accounted for possible additional costs that may result from the proposed expanded list of public OBD parameters and expanded scan tool tests in the “Research and Development Costs” of our cost analysis in Section V. EPA recognizes that there could be cost savings associated with reduced OBD testing requirements; however, we did not quantify the costs savings associated with proposed changes to the CARB's OBD testing requirements. We seek comment on our approach to including costs for OBD and the savings associated with each proposed OBD testing modification.

D. Inducements

1. Background

The 2001 final rule that promulgated the criteria pollutant standards for MY 2010 and later heavy-duty highway engines included a detailed analysis of available technologies for meeting the new emission standards. Manufacturers ultimately deployed urea-based SCR systems instead of catalyzed particulate traps and NO_X absorbers as EPA had projected in 2001. SCR is very different from these other emission control technologies in that it requires operators to maintain an adequate supply of diesel exhaust fluid (DEF), which is generally a water-based solution with 32.5 percent urea. Operating an SCR-equipped engine without the DEF would cause NO_X emissions to increase to levels comparable to having no NO_X controls at all.

As manufacturers prepared to certify their SCR-equipped engines to the EPA 2010 standards, EPA was concerned that operators might not take the necessary steps to maintain a supply of DEF to keep the emission controls working properly. To address concerns regarding the design and operation of SCR-equipped heavy-duty highway diesel engines and vehicles, between 2007 and 2012 EPA published three guidance documents, two notices and one request for comment in the Federal Register , and participated in a joint public workshop with CARB. These documents focused on the following three main categories of relevant regulatory requirements in the context of the use of DEF in SCR-equipped engines: (1) Critical emissions-related scheduled maintenance requirements, (2) adjustable parameters requirements, and (3) auxiliary emission control device (AECD) requirements. The EPA guidance identify possible approaches to meeting these regulations for heavy-duty diesel engines using SCR systems; however, the approaches were not required to be used and EPA explained that no determination was made in the guidance on whether the engine and vehicle designs that use the approaches are acceptable for certification, since that determination must be made based on the design of particular engines or vehicles. We broadly refer to this engine derate guidance as an inducement policy and design strategy. Throughout this preamble we refer to engine derates that derive from DEF-related triggers as “inducements.” This section discusses the relevant prior development and use of an inducement policy and design strategy for heavy-duty highway vehicles and engines, including comments we received on operators' experiences with inducements under that strategy in our Advanced Notice of Proposed Rulemaking, principles for updating inducement approaches for heavy-duty highway vehicles and engines, and proposed inducement provisions for heavy-duty highway vehicles and engines.

i. DEF Replenishment as Critical Emissions-Related Scheduled Maintenance

EPA regulations at 40 CFR 86.004-25 limit the emission-related scheduled maintenance that may be performed by manufacturers for purposes of durability testing and specify criteria for inclusion in manufacturers' maintenance instructions provided to purchasers of new motor vehicles and new motor vehicle engines. Of particular relevance here, the regulations in 40 CFR 86.004-25(a)(2) specify that maintenance performed on vehicles, engines, subsystems, or components used in the determination of emission deterioration factors is classified as either emission-related or non-emission-related, and either scheduled or un-scheduled. Emission-related scheduled maintenance must be technologically necessary to assure in-use compliance with the emission standards and must meet the specified allowable minimum maintenance intervals, as provided in 40 CFR 86.004-25(b) (including cross-referenced 40 CFR 86.094-25(b)(7)). Additionally, to ensure that emission controls used in the durability demonstration do not under-perform in-use as a result of vehicle owners failing to perform scheduled maintenance, manufacturers must show that all critical emission-related scheduled maintenance have a reasonable likelihood of being performed in-use (see 40 CFR 86.004-25(b)(6)(ii)).

In the guidance document CISD-07-07 signed on March 27, 2007, EPA stated that the use of DEF is consistent with the definition of critical emission-related maintenance and therefore these requirements would apply to the replenishment of the DEF tank. EPA stated that manufacturers wanting to use SCR technology would likely have to request a change to scheduled maintenance requirements per 40 CFR 86.094-25(b)(7), as the existing minimum maintenance intervals were 100,000 miles for medium-duty and 150,000 miles for heavy-duty diesel engines. Following the completion of the guidance, EPA received several requests for new maintenance intervals for SCR-equipped motor vehicles and motor vehicle engines. EPA granted these requests for model years 2009 through 2011 for heavy-duty engines in a notice that was published in the Federal Register (74 FR 57671, November 9, 2009). Engine and vehicle manufacturers provided additional requests for new maintenance intervals for vehicles and engines in model years not covered by the November 9, 2009 Federal Register notice.

In the November 9, 2009 Federal Register notice and the guidance document CISD-09-04-REVISED (CISD-09-04R), regarding the requirement that manufacturers must show that all critical emission-related scheduled maintenance have a reasonable likelihood of being performed in-use, the document explained that manufacturers could make such a showing by satisfying at least one of the conditions listed in the then-applicable 40 CFR 86.094-25(b)(6)(ii)(A-F). In particular, the guidance focused on two of the methods in the regulation: (1) Presenting information establishing a connection between emissions and vehicle performance such that as emissions increase due to lack of maintenance the vehicle performance will deteriorate to a point unacceptable for typical driving; and (2) installing a clearly displayed visible signal system approved by EPA to alert the driver that maintenance is due. In the CISD-09-04R guidance, EPA identified possible approaches to show a reasonable likelihood that DEF in a vehicle's tank will be maintained at acceptable levels.

For the first method, CISD-09-04R suggested that performance that deteriorates to a point unacceptable for typical driving would be sufficiently onerous to discourage operation without DEF. EPA suggested in CISD-09-04R that a possible approach could be for the manufacturer to include a derate of the engine's maximum available engine torque of a sufficient magnitude for the operator to notice decreased operation, explaining that a derate of at least 25 percent is likely to be needed for such an effect, and a progression to further degradation to severely restrict operation. For the second method, CISD-09-04R suggested that a clearly displayed visible signal system could include a DEF level indicator, messages in the instrument cluster, a DEF indicator, engine shutdown lamp, or audible warnings to warn the driver that maintenance is due (DEF refill is needed). The CISD-09-04R guidance reiterated that these are possible general approaches to meet the requirement that the critical maintenance is reasonably likely to occur in use, but EPA will evaluate all approaches taken by manufacturers at the time of certification, and such evaluation will be based on the requirements in the regulations.

On January 5, 2012 (77 FR 488), EPA updated and extended its approval of maintenance intervals for the refill of DEF tanks for heavy-duty engines for 2011 and later model years. In a separate rulemaking in 2014, EPA added DEF tank size (which dictates DEF replenishment rate) to the list of scheduled emission-related maintenance for diesel-fueled motor vehicles and motor vehicle engines in 40 CFR 86.004-25(b)(4)(v). We are proposing to migrate this provision into new 40 CFR 1036.115(i).

EPA also added a limitation in 40 CFR 86.004-25(b)(5)(ii) for DEF replenishment (a critical emission-related scheduled maintenance item), requiring that manufacturers must satisfy paragraph (b)(6)(ii)(A) or (F) to be accepted as having a reasonable likelihood of the maintenance item being performed in-use. EPA explained that the criteria in (b)(6)(ii)(B)-(E) were not sufficiently robust for DEF replenishment, and therefore would not be sufficient for demonstrating that DEF replenishment is reasonably likely to occur in use. We are proposing that the proposed inducement requirements in 40 CFR 1036.111 will ensure the reasonable likelihood of DEF replenishment being performed in-use. EPA is not proposing any changes to DEF refill intervals. We are proposing to exclude the alternative option in (b)(6)(ii)(F) to demonstrate DEF replenishment is reasonably likely to be performed in-use, but are seeking comment on whether this provision should instead be preserved. EPA is otherwise proposing to migrate the provisions in 40 CFR 86.004-25(b)(5)(ii) to 40 CFR 1036.125(a)(1) (section IV.D.3. describes the proposal in detail).

ii. DEF as an Adjustable Parameter

EPA regulations in 40 CFR 86.094-22(e) require that manufacturers comply with emission standards over the full adjustable range of “adjustable parameters” and state that we will determine the adequacy of the limits, stops, seals or other means used to inhibit adjustment. For any parameter that has not been determined to be adequately limited, 40 CFR 86.094-22(e) authorizes the Administrator to adjust the parameter to any setting within the physical limits or stops during certification and other testing. In determining the parameters subject to adjustment, EPA considers the likelihood that settings other than the manufacturer's recommended setting will occur in-use, considering such factors as, but not limited to, the difficulty and cost of getting access to make an adjustment; damage to the vehicle if an attempt is made; and the effect of settings other than the manufacturer's recommended settings on engine performance. Adjustable parameters historically included things like physical settings that are controlled by a dial or screw.

In guidance document CISD-07-07, EPA provided clarification that an SCR system utilizing DEF that needs to be periodically replenished would meet the definition set forth in paragraphs 40 CFR 86.094-22(e)(1) and 86.1833-01(a)(1) and could be considered an adjustable parameter by the Agency. EPA is confirming that DEF is considered an adjustable parameter because it is both physically capable of being adjusted and significantly affects emissions. In particular, DEF level and quality are parameters that can physically be adjusted and may significantly affect emissions. SCR system designs rely on storing DEF in a tank located on the vehicle, the operator refilling the tank with quality DEF, and quality DEF being available. This design depends on the vehicle operator being made aware that DEF needs to be replaced through the use of warnings and vehicle performance deterioration. The EPA guidance CISD-07-07 described that without a mechanism to inform the vehicle operator that the DEF needs to be replaced, there is a high likelihood that the adjustable parameter will be circumvented or exceeded in-use and therefore EPA would not consider the system to be adequately inaccessible or sealed. EPA stated in CISD-07-07 that we would not prescribe a specific driver inducement design, but that the options identified in the guidance could be utilized to demonstrate that the driver inducement design was robust and onerous enough to ensure that engines will not be operated without DEF in the vehicle ( e.g., if the operator ignored or deactivated the warning system). In addition, the guidance stated that the driver inducement mechanism should not create undue safety concerns, but should make sure vehicle operators are adding DEF when appropriate by having the vehicle performance degraded in a manner that would be safe but would be onerous enough to discourage vehicles from being operated without DEF. EPA stated that the key challenge of this approach is to determine what would constitute an acceptable performance degradation strategy.

EPA guidance document CISD-09-04R re-emphasized that under the adjustable parameter requirements, EPA makes a determination at certification whether the engine is designed to prevent operation without quality DEF. The guidance suggested a similar strategy for both DEF level and quality could be used, which would alert the operator to the problem and then use a gradually more onerous inducement strategy to either fill the tank or correct the poor-quality DEF and discourage its repeated use. CISD-09-04R also provided more detail on the potential use of inducements with tamper resistant designs to reduce the likelihood that the adjustable parameters will be circumvented in use, noting that in particular, manufacturers should be careful to review the tamper resistance of the system to prevent the disconnection of certain components ( e.g., DEF pump or dosing valve). EPA did not determine in CISD-07-07 what specific amount of time or mileage would be necessary for an inducement policy. EPA guidance document CD-13-13 was issued in November 2013 in response to concerns that operators may dilute DEF with water to reduce costs. CD-13-13 provides guidance to manufacturers of heavy-duty on-highway engines on how EPA expects to determine the physical range of adjustment of DEF quality for certification testing. EPA explained that we generally would consider the range of adjustment for emission testing to span the change in urea concentration from 32.5 percent (unadulterated DEF) to the point at which poor DEF quality can be detected. This guidance also provides possible measures manufacturers may take, such as inducements, to sufficiently restrain the adjustment of DEF quality to limit the need for testing outside the manufacturer's specified range. EPA is proposing to adopt certain performance degradation strategy requirements that must be met for EPA to make a determination at certification that the engine is designed to prevent operation without quality DEF under the adjustable parameter requirements (section IV.D.3. describes the proposal in detail).

iii. DEF Usage and Auxiliary Emission Control Devices (AECDs)

In CISD-09-04R EPA discussed that under extreme temperature conditions DEF may freeze and not immediately flow to the SCR system. There are, however, systems and devices that can be utilized to ensure the flow of DEF. These systems are evaluated as AECDs (see 40 CFR 86.082-2) and manufacturers must describe this AECD and show that the engine design does not incorporate strategies that reduce emission control effectiveness compared to strategies used during the applicable Federal emissions test procedures. EPA examines systems during certification for ensuring proper dosing during extreme conditions such as cold weather operation. CISD-09-04R provided an example of a test procedure that could be used for ensuring the SCR system has adequate DEF freeze protection. Under this example, SCR systems that are capable of fully functional dosing at the conclusion of the test procedure might be considered acceptable. EPA is not proposing any changes to existing regulatory requirements for AECDs or to supersede guidance with our proposed requirements, if finalized, except as explicitly identified in section 40 CFR 1036.111.

iv. Tamper-Resistance Design

The existing EPA guidance and this section discuss inducements as a tamper-resistant design strategy in the context of steps manufacturers can take to prevent operation without quality DEF. Under the CAA, engines must meet emission standards promulgated under section 202(a) throughout useful life. Engines that do not meet those standards throughout useful life may result in increased emissions that fundamentally undermine EPA's emission control program and prevent us from realizing the intended improvements in air quality. Tamper-resistant design in engines can be an important part of a manufacturer's compliance strategy to ensure that emissions standards are met in-use throughout useful life. In addition to the reasons described in the cited guidance documents, an inducement strategy for SCR-system tamper-resistance can be part of a manufacturer's demonstration at certification that engines will be built to meet emission standards in-use throughout useful life.

The Agency believes that combining detection of open-circuit fault conditions for SCR components ( i.e., disconnection of SCR components) with inducements would decrease the likelihood that the SCR system will be circumvented through tampering.

2. ANPR Comments on the EPA's Inducement Guidance

The ANPR requested comment on EPA's existing guidance related to SCR and DEF. A majority of the comments expressed concern that despite the use of high-quality DEF and in the absence of tampering, in-use vehicles are experiencing inducements for reasons outside of the operator's control. Commenters stated that the reasons for these types of inducements are often difficult to diagnose and can lead to repeat trips to a repair facility and additional costs. Commenters also stated that the existing schedule and speeds are not necessary to achieve EPA's compliance goals, and instead the severe nature of these concerns may be leading to unusual tampering rates. This section summarizes the submitted comments.

Several commenters described problems with repeated occurrences of inducements even with the use of a sufficient quantity of high-quality DEF and in the absence of tampering ( i.e., a “false inducement”). They reported that some of these cases were traceable to incidents where the system detected a problem that did not exist and did not create emission concerns, for example a vehicle with a full DEF tank experienced an inducement due to a faulty DEF level sensor which reported an empty tank. Commenters stated that false inducements can occur, for example, as a result of software glitches, wiring harness problems, minor corrosion of terminals, or faulty sensors, even if those problems have no effect on the function of the emission control system.

Commenters stated that “no trouble found” events were common where repair technicians were unable to diagnose a system fault after the engine triggered an inducement. This condition has also been documented by manufacturers who have issued technical service bulletins (“TSBs”) discussing such concerns. EPA has identified a significant number of TSBs documenting in-use problems that cause erratic fault codes which can lead to inducements or engine derate despite operators using high-quality DEF and not tampering. For example, some TSBs describe faulty wire harness routing problems that can cause inducements and recommend fixes that include adding extra zip ties or tape. Commenters noted that erratic system problems can lead to “defensive repairs” as a diagnostic strategy for returning the vehicle to service, which could result in repair expenses for replacing parts that are not faulty and add risk of future costs if the problem reoccurs, repeated tows are required, further diagnosis is done, and more repairs are attempted. Commenters expressed a particular concern for intermittent fault conditions that make diagnosis especially difficult. To alleviate such concerns, ATA commented that EPA should eliminate inducements for reasons other than maintaining an adequate supply of high-quality DEF. ANPR commenters also expressed a concern that technicians might repair a defective part without addressing the root problem that caused the part to fail, which again leads to repeated experiences of towing and repairing to restore an engine to proper functioning.

Commenters stated that, despite their continued diligence to use high-quality DEF, they have repeated experiences with inducements resulting in very onerous costs. Some commenters noted they were subject to the most severe restrictions multiple times per year even though DEF tanks were properly filled. OOIDA commented that inducement-related costs can severely jeopardize owner-operators' ability to stay in business, citing costs that included towing and lost income from downtime in addition to diagnosis and repair. Commenters were especially concerned with long-distance routes, which might involve a vehicle that is several days distant from the base of operations. Other commenters highlighted that service information and tools should be made easily available and affordable for individual owners to diagnose and fix their own vehicles, which can be important for small businesses, Tribes, and those in rural areas with less ready access to original equipment manufacturer dealer networks. While these comments did not specifically discuss inducements, EPA also considers these comments relevant to vehicles that are in an inducement condition. Other commenters added that false inducements in these situations can necessitate having engines serviced at an unfamiliar repair facility that has no information on a given vehicle's repair history, which can result in improper repairs and increased travel expenses for drivers to return home.

Commenters stated that the four hours of operation before engines reach final inducement is poorly matched with typical wait times of three or four days before repair technicians can look at and attempt to diagnose the problem with their vehicles, plus additional time is needed to complete the repairs. Commenters further stated that repair technicians are often unable to diagnose the problem, repairs can take several days in any case, with additional time lost if there is a need to order parts and wait for shipment, and there are frequently “come-back” repairs for vehicles not fixed properly the first time.

Commenters stated that the money needed for a tow would be better spent on repairs. Some commenters emphasized that a speed restriction of 5 mph caused the need for towing, even though a less restrictive inducement would accomplish the same purpose without incurring towing expenses.

Commenters described experiences of sudden inducements restricting vehicle speed to 5 mph which they stated caused highway safety problems for truck drivers and nearby vehicles. Others described having safety concerns when a vehicle is stranded, such as having buses carrying passengers parked along the highway or freeway.

Some commenters stated that in addition to monetary costs, there are other business impacts such as missing critical deadlines, loss of customer trust and credibility, and loss of future contracts. Other comments indicate that EPA's existing inducement policy, especially where application of it has resulted in false inducements, may have created a strong incentive to either tamper with SCR systems ( e.g., installing “delete kits”) and may be leading to owners extending the life of older vehicles; they further asserted that these behaviors were causing trucks to fail to accomplish the intended emission reduction goal. For example, the American Truck Dealers division of National Auto Dealers Association commented that in addition to emission-related maintenance and repair issues, improperly functioning SCR derate maintenance inducements have also led to emissions tampering.

It is worth noting that in comments on CARB's Omnibus rule both the California Trucking Association and ATA member companies requested CARB work with EPA to further investigate the efficacy of progressive de-rate inducements typically associated with low-volume or empty DEF tanks or the use of poor-quality DEF. They added that the safety and environmental implications of these types of de-rate occurrences need additional evaluation and study prior to enacting additional NO_X controls. Further, they commented that following more than a decade of experience, de-rates not related to low DEF levels or inferior DEF quality continue to occur, and that among a sampling of fleets operating more than 10,000 trucks, nearly 80 percent of de-rates in 2019 were attributed to other causes such as sensor failures, electrical defects and SCR component issues. ATA stated that many of these causes are not associated with the emissions performance of the SCR system and yet are initiating operational restrictions. After the ANPR was issued, EPA received a letter from charter bus companies detailing their concerns and difficulties experienced with existing inducements. Specifically, they mentioned the inadequate timeframe for which to resolve problems, the safety risk to passengers, the high cost of towing, other costs incurred due to breakdowns such as reimbursements owed for tickets to missed shows or flights, and the cost to their reputation despite their efforts to maintain their fleets and keep the emissions systems functioning properly.

3. Principles for Updating Inducement Provisions

In general, emission control technology is integrated into engine and vehicle systems in ways that do not require routine operator interaction. However, ensuring that on-highway engines using SCR are designed, consistent with our regulations, to prevent operation without quality DEF through and dependent upon steps performed by operators in-use presents unique challenges. Crafting an inducement policy includes complex technological questions on how manufacturers should demonstrate that SCR system standards and related requirements will be met and challenging policy decisions on how to appropriately motivate or restrict certain types of human behavior that are either necessary for or directly impact in-use compliance with emissions standards. EPA recognizes and commenters have highlighted that the existing inducement policy and its implementation have resulted in a complex mix of incentives and behaviors. Policymaking for inducements therefore presents itself not as an engineering problem with a single solution.

EPA is proposing to codify inducement provisions, which include adjustments as compared to our existing inducement guidance after consideration of manufacturer designs and operator experiences with SCR. We recognize that SCR technology has continued to mature, and appropriate designs for heavy-duty engines using SCR systems have evolved over the past decade. EPA continues to believe that designing SCR-equipped engines with power derating is an effective and reasonable measure to ensure that operators perform critical emissions-related scheduled maintenance on the SCR system and to demonstrate to EPA that it is reasonable to anticipate, consistent with requirements for adjustable parameters, that the engine would normally be operated using quality DEF. We are proposing inducement requirements whose objective is to ensure that emission controls function and emission reductions occur in-use while reducing potential impacts to operators through the consideration of the following key principles.

EPA's inducement approach should result in:

1. Operators maintaining an adequate supply of high-quality DEF while discouraging tampering of SCR systems,

2. a speed derating schedule for inducement that balances impacts to operators while still achieving required emission control,

3. unique inducement schedules for different categories of vehicles that reflect different primary operating conditions to ensure that the final inducement speed is effective while acknowledging operating constraints,

4. ensuring that the inducement condition is warranted,

5. clear communication of SCR system problems to the operator,

6. avoiding the need for intervention at a dealer or other specialized service center where possible, and

7. reduced likelihood of in-use tampering based on a more targeted inducement approach.

Development of regulatory inducement requirements that reflect these key principles requires consideration of potentially competing concerns. A minimally restrictive approach might result in increased emissions because of extensive operation without scheduled maintenance being performed and circumvention of the limit on the adjustable range ( i.e., without use of sufficient high-quality DEF). In contrast, an overly restrictive approach might impose unnecessary costs and pose a threat to operators' livelihoods, as well as leading to potentially increased tampering with engines or reduced fleet turnover rates that would lead to increased emissions.

The principles described here are those EPA used to develop the proposed inducement provisions in 40 CFR 1036.111 and are discussed later in this section for heavy-duty engines certified under 40 CFR part 1036 that use SCR systems. These principles are based on our existing guidance but include important adjustments. The first principle is to develop an effective inducement proposal that ensure that all critical emission-related scheduled maintenance has a reasonable likelihood of being performed and allows manufacturers to demonstrate an acceptable performance degradation strategy at the time of certification to meet adjustable parameter requirements. This principle should result in a proposal that would ensure operators will add high-quality DEF and would help prevent tampering with the SCR system by requiring increased levels of inducement to occur in stages for reasons related to insufficient quantity of high-quality DEF or tampering with the SCR system. This approach creates an immediate and increasing incentive to remedy the problem. Operators would keep tanks full of high-quality DEF prior to the inducement process starting and avoid tampering with the SCR system.

Our second principle seeks to identify an appropriate speed derating schedule for inducements that reflects experience gained over the past decade with SCR. This schedule would better balance impacts to operators while ensuring that all critical emission-related scheduled maintenance has a reasonable likelihood of being performed and allow manufacturers to demonstrate an acceptable performance degradation strategy at the time of certification to meet adjustable parameter requirements. An appropriate inducement speed and schedule should be low enough to ensure that operators maintain a supply of high-quality DEF, while allowing engines to operate at a limited speed over a restricted timeframe that restricts commercial operation ( e.g., highway operation) but allows for safely operating the vehicle to return home for repair and to perform the necessary post-repair diagnostic checks to avoid “come-back” repairs. Almost all heavy-duty vehicles are engaged in commercial activity for which it would be completely unacceptable to operate indefinitely at vehicle speeds that do not allow for travel on limited-access highways. This principle should result in an inducement schedule that would allow a reduced level of operation over a sufficient period of time for operators when there is a need to get a driver home from a distance, deliver critical freight ( e.g., passengers, livestock, or concrete) or for scheduling repairs in a time or area of limited openings in repair shops. Establishing an inducement policy that would be consistent among manufacturers would improve operator experiences. For example, today manufacturer strategies may differ in ways that potentially may have significant effects on operators ( e.g., some manufacturers implement a final severe inducement only after a vehicle is stopped, others implement it immediately while a vehicle is in motion). EPA believes another important aspect of this principle is to set an inducement schedule that would include additional stages of derated engine power that would be tied to drive-time to create a predictable schedule of increasing incentive to repair the engine. We also believe that our proposed approach, including the proposed inducement speeds and schedules, would be the most effective way to minimize operational disruptions due to potential supply chain problems such as component or DEF shortages.

The third principle is to recognize the diversity of the real-world fleet and that one inducement schedule may not be appropriate for the entire fleet. Instead, separate inducement speeds and schedules should apply to vehicles that primarily operate at low- or high-speeds to ensure an appropriate final inducement is applied. Certain vocational vehicles, such as utility trucks, local delivery vehicles, refuse trucks, cement mixers, and urban buses do not operate fast enough to be effectively constrained by the same inducement speed that would be appropriate for trucks with extended highway driving. Similarly, applying a low final inducement speed to the entire fleet would overly constrain vehicles that spend the majority of their time at highway speeds. Rather than the EPA identifying a different inducement schedule for each type of vehicle, vehicles would be subject to an alternative inducement schedule based on the average vehicle speed history recorded in the onboard computer.

The fourth principle would not apply an inducement if there is a fault code flagged by the system but the SCR system is still controlling NO_X emissions. Under this principle, putting a vehicle into an inducement for a condition that does not result in a failure of the engine to comply with emission standards would be inconsistent with the goal of an inducement policy. To apply inducements consistent with this principle, manufacturers would design their diagnostic system to override a detected fault condition if NO_X sensors confirm that the SCR system is in fact appropriately reducing NO_X emissions. The diagnostic system depends on multiple sensors and complex algorithms to detect fault conditions. This override feature could be helpful to reduce false inducements that can occur when the fault is not due to tampering or the absence of high-quality DEF in the system ( e.g., a faulty DEF level sensor in a tank full of DEF). An inducement approach that includes a backup check would address problems with faulty sensors or part shortages that can strand owners. Under CARB's updated 2019 OBD regulations, which apply under CARB's regulations starting with MY 2023 compliant OBD systems would be able to query data in the most recent “active 100-hour array”, which monitors and records the most recent engine and emission control parameters at discrete operating conditions to confirm that appropriate NO_X reductions are occurring. We are proposing to incorporate by reference these updated CARB OBD requirements and to make them mandatory for MY 2027 and later, while manufacturers could voluntarily choose to certify to these requirements prior to that (see section IV.C.1. for further discussion on OBD).

The fifth principle seeks to improve the type and amount of information operators receive from the truck to help avoid or quickly remedy a problem that is causing an inducement. This could include manufacturers providing information on the dashboard or other display to indicate when the first (and next) stage of derating will start in addition to identifying the current (and next) restricted speed. It is important for operators to understand what is happening to the truck as well as whether or not they can make it back home or to a preferred repair facility and reduce anxiety that can occur when an inducement or engine derate occurs. The indicator would also show the fault condition that caused the inducement. This status information would help to prevent an unsafe condition resulting from an unexpected step down in speed, and it would give operators important information for planning routes to arrange for repairs.

The sixth principle includes allowing operators to perform an inducement reset by using a generic scan tool or allowing for the engine to self-heal through the completion of a drive cycle that will warm up the SCR system to operating temperature and permit the system to automatically reset the inducement condition as appropriate. This approach would allow vehicle owners much more discretion to perform repairs themselves or select appropriate repair facilities for their vehicles. This flexibility becomes increasingly important as vehicles get older, especially for second or third owners, who typically depend on simpler maintenance procedures to keep operating costs low enough for viable operation. Any system reset that does not follow the fault condition being addressed would require the engine to immediately return to the stage of inducement that applied before the reset, which would address the risk of improper resets. Together with allowing more time to diagnose and repair a vehicle, this provision would help to address comments from Tribal interests stating that Tribes and others operating in remote areas often have limited access to dealers or specialized repair facilities for repairing engines including vehicles that are in an inducement condition. These provisions would increase options available to all vehicle owners and small fleets who perform their own repair and maintenance and may be unable to service their own vehicles if the fault condition occurs any distance from the home base. A higher proposed final inducement speed would also allow the OBD system to run an internal diagnostic check to confirm that the fault condition is no longer active and that the SCR catalyst is again reducing NO_X emissions. This would be especially important for vehicle owners that do their own repair work on older vehicles or for operators in remote areas with limited access to dealers and specialized tools.

The seventh principle seeks to develop an inducement schedule that will ensure scheduled maintenance has a reasonable likelihood of being performed and allow manufacturers to demonstrate they meet adjustable parameter requirements at the time of certification while addressing operator frustration with false inducements and severe inducement speed restrictions that may potentially lead to in-use tampering of the SCR system. We are concerned that engine designs that may have been intended to be responsive to the existing SCR guidance may have resulted in high levels of false inducement and overly restrictive speed limitations and may have increased in-use tampering. For example, there are many technical support bulletins that have been released by manufacturers that detail inducements occurring for reasons outside of operator control, such as minor corrosion on electrical connectors. In addition, we received comments on the ANPR regarding false inducements leading to emissions tampering. EPA is aware there are products available in the marketplace to facilitate tampering through the removal of SCR systems, which might be being unlawfully used by vehicle owners who are adversely affected by false inducements. After a decade of experience with SCR-equipped engines and existing EPA guidance, several of the initial concerns with the use of SCR that formed the basis of some elements of the existing guidance have been resolved. DEF is widely available and the cost of DEF at the pump is not that different from the cost of distilled water. A less restrictive approach could be equally effective at encouraging operators to maintain a supply of DEF, without causing problems that may be leading to increased in-use tampering. A less restrictive inducement schedule would allow operators more flexibility for on-time delivery, reduce operator costs by allowing vehicles to be driven to repair shops thereby avoiding towing fees, and allow more time for proper diagnosis and repair to reduce the need for repeat visits to repair shops.

These seven principles, which include improved diagnostic fault communication, NO_X override checks, and revised inducement speeds and schedules that reflect more realistic vehicle operations, would result in a program that more effectively maintains in-use emission reductions. We believe the proposed provisions described in the following section would provide a net benefit to fleet operators, small businesses, and the environment.

4. Proposed Inducement Provisions

Consistent with the seven principles described in Section IV.D.3. EPA is proposing to specify in 40 CFR 1036.125(a)(1) that manufacturers must meet the specifications in 40 CFR 1036.111 to demonstrate that DEF replenishment is reasonably likely to occur at the recommended intervals on in-use engines and that adjustable parameter requirements will be met. We are proposing to exclude the alternative option in 40 CFR 86.004-25(b)(6)(ii)(F) to demonstrate DEF replenishment is reasonably likely to be performed in use and are seeking comment on whether manufacturers should be allowed to ask for approval to use an alternative method of compliance to meet these requirements. Consistent with the existing guidance, the proposed requirements would codify that SCR-equipped engines must meet critical emission-related scheduled maintenance requirements and limit the physically adjustable range under the adjustable parameter requirements by triggering inducements. EPA is proposing to adopt requirements that inducements be triggered for fault conditions including: (1) DEF supply is low, (2) DEF quality does not meet manufacturer specifications, or (3) tampering with the SCR system. EPA is also proposing separate inducement schedules for low- and high-speed vehicles. The proposed inducement requirements would include a NO_X override to prevent false inducements. EPA is proposing to require manufacturers to improve information provided to operators regarding inducements. The proposal also includes a provision to allow operators to remove inducement conditions after repairing the engine either through the use of a generic scan tool or through a drive cycle to ensure that repairs have been properly made. EPA is proposing that if multiple repeat fault conditions are detected that the inducement schedule would not restart with each new fault.

The proposed inducement provisions include several aspects. The first three described here relate to proposed inducement triggers in 40 CFR 1036.111. First, EPA is proposing to require inducements related to DEF quantity to ensure that high-quality DEF is used, similar to the approach described in our existing guidance. Specifically, we propose that SCR-equipped engines must trigger the start of an inducement when the amount of DEF in the tank has been reduced to a level corresponding to three hours of engine operation.

Second, EPA proposes to require inducements related to DEF quality to ensure that high-quality DEF is used, similar to the approach described in our existing guidance. There was a concern when SCR was first introduced into the market a decade ago that DEF availability may be limited and some operators may choose to use poor quality DEF, or, for example, dilute DEF with water to reduce operating costs. DEF quickly became widely available and today is conveniently available even in pump form ( e.g., next to diesel pumps at refueling stations) to refill DEF tanks while refilling diesel tanks. Modern engines are designed with feedback controls to increase or decrease DEF flow as the system detects that a greater or lesser quantity of DEF is needed to supply the amount of urea needed to keep the SCR catalyst working properly or trigger an inducement. This DEF dosing feedback removes any practical incentive for diluting DEF, as any such attempt would result in more volume of DEF being consumed and trigger an inducement when emissions control is no longer possible. Further, OEMs have made clear to operators that using water without urea would cause extensive engine damage and void the warranty. Today, the per-gallon price of DEF at the pump is closer to the price of a gallon of distilled water. Given an operator's ability to physically adjust DEF quality and the increase in NO_X emissions that would result if they do so, EPA maintains that DEF quality is an adjustable parameter and is proposing to require inducements when DEF quality fails to meet manufacturer concentration specifications. Due to widespread DEF availability and familiarity with operators, EPA believes operators would readily find and use high-quality DEF to avoid inducements. As discussed in Section IV.D.1.ii, CD-13-13 provides guidance on DEF quality as an adjustable parameter. The guidance states that EPA generally considers the range of adjustment for emission testing to span the change in urea concentration from 32.5 percent (unadulterated DEF) to the point at which poor DEF quality can be detected. This point represents the limit for DEF quality adjustment because it is the first point at which a manufacturer is able to implement inducements to prevent sustained engine or vehicle operation with poor quality DEF. EPA is not proposing changes to this guidance.

Third, EPA is proposing to require inducements to ensure that SCR systems are designed to be tamper-resistant to reduce the likelihood that the SCR system would be circumvented, similar to the approach described in our existing guidance. CISD-09-04R discusses tamper-resistant design with respect to a list of engine components in the SCR system and suggests that manufacturers could design these components to be physically difficult to access in addition to using warnings and inducements if they are disconnected. We are proposing to require monitoring for and triggering of an inducement for tampering with the components listed in CISD-09-04R, as well as for a limited number of other components. Specifically, we are proposing that open-circuit fault conditions for the following components trigger inducements if detected, to prevent disconnection through tampering: (1) DEF tank level sensor, (2) DEF pump, (3) DEF quality sensor, (4) SCR wiring harness, (5) NO_X sensors, (6) DEF dosing valve, (7) DEF tank heater, and (8) aftertreatment control module (ACM). Monitoring the DEF tank heater is important to ensure AECD requirements are met. We are not proposing to include the language from CISD-09-04R that such components should be designed to be physically difficult to access because an inducement condition would be triggered upon the unplugging of a component ( i.e., an open-circuit condition). Similar to the approach described in CISD-09-04R which specified that disconnection of the SCR wiring harness could trigger inducements as a tamper-resistant design strategy, we are proposing to specify that the ACM also be monitored for disconnection. In addition to proposing to require detection of open-circuit conditions for certain components to prevent tampering, EPA is also proposing to require that manufacturers trigger an inducement for blocked DEF lines or dosing valves similar to the approach described in CISD-09-04R. EPA is proposing that all inducement-related diagnostic data parameters be made available with generic scan tools (see section IV.C.1.iii.b. for further information). Finally, EPA is proposing to require that manufacturers monitor for a missing catalyst (see OBD requirements for this monitor in 13 CCR 1971.1(i)(3.1.6)) and trigger an inducement if this condition is found.

As indicated in ANPR comments summarized in Section IV.D.2, many operators report experiencing false inducements from faulty hardware that are not a result of tampering. These experiences may indicate that the existing triggers for inducements in engines may be too aggressive, or that OEMs may not be able to clearly distinguish between tampering and faulty hardware. EPA reviewed various manufacturer's inducement strategies in their certification documents and compared those to our existing guidance. Some manufacturers have certified engines with nearly 200 different reasons for an engine to go into a derate condition, including nearly 50 reasons for an SCR-related inducement. Many of the derates are for engine protection, and we are not proposing to make any changes to these types of derates. However, we are adopting a list of SCR system inducement triggers for meeting critical emissions-scheduled maintenance and adjustable parameter requirements that focus on specific emission control components and conditions that owners can control such as disconnecting a DEF pump or other SCR-related emission control hardware. The proposed list includes the tamper-resistance inducement triggers included in CISD-09-04R as well as additional components. We believe that standardizing the list of tampering inducement triggers would aid owners, operators, and fleets in the repair of their vehicles by reducing the cost and time required to diagnose the reason for inducement.

Fourth, we are proposing separate four-step derate schedules and final inducement speeds for vehicles that operate at low and high speeds as shown in Table IV-13. We are proposing that the application of low-speed inducements (LSI) and high-speed inducements (HSI) be based on an individual vehicle's operating profile. In particular, vehicles that have a stored average vehicle speed below 20 mph during the previous 30 hours of engine operation (not including idle time) would be considered low-speed vehicles and be subject to an LSI. Excluding idle from the calculation of vehicle speed allows us to more effectively evaluate each vehicle's speed profile, not time spent idling, which does not impact the effectiveness of a final inducement speed. EPA chose this speed based on an analysis of real-world vehicle speed activity data from the FleetDNA database maintained by the National Renewable Energy Laboratory (NREL). Our analysis provided us with insight into the optimum way to characterize high-speed and low-speed vehicles in a way to ensure these categories received appropriate inducements that would not be ineffective or overly restrictive.

EPA is proposing to require specific inducement schedules for low-speed and high-speed vehicles. We are proposing to codify progressively increasing inducement derate schedules that allow the owner to efficiently address conditions that trigger inducements. Table IV-13 shows the proposed default four-step inducement schedules in cumulative hours. The time spent in each stage of inducement would include time spent idling. The initial inducement of either 50 mph or 65 mph would apply immediately when the OBD system detects: (1) There is approximately three hours-worth of DEF remaining in the tank, (2) DEF quality fails to meet manufacturers' concentration specifications, or (3) when certain SCR system tampering events have occurred. The inducement schedule would then step down over time to result in a final inducement speed of either 35 mph or 50 mph depending on individual vehicle operating profiles. In determining the appropriate final inducement speeds for this proposal, EPA also relied in part on analysis of data in the NREL FleetDNA database. Analyzing potential impacts of final inducement speeds based on vehicle applications involves a number of different considerations, beyond how much time a particular application spent at different speeds. For example, the ability to achieve higher speeds may be critical to many different duty cycles and logistics necessary for commercial activities. Inducements are intended to reduce/eliminate the ability to perform work such that operators will replenish the tank with high-quality DEF and not tamper with the SCR system. For example, our data show that combination long-haul vehicles spend nearly almost 40 percent of their driving time over 65 mph. Based on this operation, an inducement speed of 65 mph will cause a significant impact on the ability of the vehicle to be used for commercial purposes, which means that any speed restriction below this threshold is less likely to further incentivize operators to keep emissions systems compliant. In addition, there were other segments that may operate at lower average speeds, but when looking at their duty cycle, it is clear that they depend on being able to complete their work by achieving high rates of speed frequently, although not for sustained periods ( e.g., delivery vehicles that return to a warehouse multiple times throughout the day to reload). These vehicles may travel at lower speeds with frequent stop and go operation during delivery but may need to travel on the highway to return to the warehouse in order to complete a certain number of operations in a day. Many vehicle segments in our sample exhibited this type of duty cycle with frequent higher speeds, for example, some single short-haul vehicles that had average speeds under 20 mph had duty cycles that reached 60-70 mph briefly every hour.

We are proposing that the inducement schedules for low- and high-speed vehicles include four stages that ramp down speeds to the final LSI and HSI. The first stepped decrease in speed would apply six hours after the initial inducement, which allows time for operators to fill the DEF tank and resume operation in a way that allows the engine to confirm a proper DEF supply without starting the next stage of inducement. If the fault code is not resolved, the schedule continues to reduce the vehicle speed by 5 mph increments in two additional stages. One of the considerations in choosing the stepped speed decreases is allowing drivers time to safely adjust to operation at a lower speed while also adequately incentivizing action by vehicle owners and operators, and we are proposing that 5 mph increments achieve this balance. Commenters noted that even small changes in allowable speeds are sufficient incentive to use high quality DEF. Further, we believe the first step of our proposed inducement policy would result in the use of high-quality DEF. The proposed additional time would also allow for the diagnosis and repair of more extensive problems and intermittent conditions.

The low-speed vehicle schedule and the final LSI speed of 35 mph is designed for vehicles such as urban buses, school buses, and refuse haulers that have sustained operation at low speeds, but frequently travel at high speeds. Further, the final LSI speed would also apply to concrete trucks, street sweepers, or other utility vehicles that have low average speeds, but depend on higher speed operation to get to a job site. In part, because of this high-speed operation, the final LSI speed will be effective for compelling operators to properly maintain their aftertreatment systems. The high-speed vehicle schedule and the final HSI speed of 50 mph is designed for vehicles such as long-haul freight trucks that have sustained operation at high speeds. The final restricted speed of 50 mph prevents the vehicle from travel on most interstate highways with state laws regarding impeding traffic and may require the operator to use flashers to warn other vehicles of the reduced speed.

We expect that the proposed derate schedules would be no less effective than the current approach under existing guidance for ensuring operators properly maintain aftertreatment systems and that it would result in lower costs and impacts to operators and ultimately result in lower tampering rates. EPA recognizes that the fleet is very diverse, and believes that applying two inducement schedules and speeds is an effective and reasonable approach that is not too aggressive or too inconsequential to ensure operators maintain compliance. Our analysis and proposed LSI and HSI schedules are intended to achieve the proper balance and limit unintended consequences such as increased tampering.

Sixth, to reduce occurrences of false inducements, the proposed inducement approach would require a warning to be displayed to the operator to indicate a fault, but utilize a NO_X override feature to prevent false inducement. We are proposing that an inducement would not be triggered if average data from the NO_X sensor show that the catalyst is reducing NO_X emissions consistent with stored OBD REAL Bin data within an estimated 10 percent margin of error due to limitations of in-use detection and measurement. A 10 percent reduction in NO_X conversion efficiency has been selected because the accuracy of the NO_X measurement can have errors as much as 10-20 percent based on a study conducted by SwRI. This NO_X sensor error increases as the NO_X concentration is reduced. Using a 10 percent error is a reasonable threshold based on the work completed by SwRI and considering continuing advances in technology of on-board NO_X sensors.

For vehicles subject to a HSI, this data would come from Bin 14 which holds data taken during operation at vehicle speeds greater than 40 mph and when the engine power output is greater than 50 percent of rated power. For vehicles subject to a Low Speed Inducement (LSI), this data would come from Bin 13 which holds data taken during operation at vehicle speeds greater than 25 mph and less than or equal to 40 mph and when the engine power output is greater than 50 percent of rated power. This data would indicate whether DEF is present in the system as zero NO_X reductions would occur without DEF, and data showing reductions consistent with operation prior to the condition would indicate that the operator is adding high-quality DEF. We propose that the NO_X sensor data used to evaluate the need for inducement would come from the 100-hour active array, which would be reset at the time an initial inducement trigger occurred. Resetting the array at that time would ensure that the data used to evaluate whether sufficient high-quality DEF is present in the system would be taken after the initial inducement was triggered and not rely on historical data to make the assessment. The OBD system would continue to monitor the fault condition and provide a warning to the operator that an issue should be addressed, but an inducement would not be triggered unless NO_X performance fell below the threshold of a 10 percent reduction in NO_X conversion efficiency ( e.g., indicating that the operator has not added DEF).

Seventh, as discussed in section IV.D.3, EPA is proposing in 40 CFR 1036.111(f) that manufacturers must display the condition that triggered the pending or active derate and a countdown timer to estimate the time or distance remaining before the next stage of derating. This display requirement would apply even if the engine overrides a detected fault condition based on NO_X measurements, and the display should indicate that the derates will not apply as long as NO_X sensors continue to show that emission controls are functioning properly. It is critical that operators have clear and ready access to information regarding inducements to reduce potential anxiety over progressive engine derates (which can lead to motivations to tamper) as well as to allow operators to make informed decisions.

Eighth, we are proposing that the system would remove the inducement and resume unrestricted engine operation once the OBD system detects the condition has been remedied. EPA would also expect manufacturers to enable the system to reset once the problem was repaired. EPA is proposing to require that generic scan tools be able to remove an inducement condition. This would allow owners who repair vehicles outside of commercial facilities to complete the repair without delay ( e.g., flushing and refilling a DEF tank where contaminated DEF was discovered). However, if the same fault condition repeats within 80 hours of engine operation ( e.g., in response to a DEF quantity fault an owner adds a small but insufficient quantity of DEF), we are proposing that the system would treat the reoccurring fault condition as the same triggering condition and immediately resume the derate at the same point in the derate schedule where it was last deactivated. In addition, we are proposing that the Active 100 Hour Array would not be reset if an additional fault occurs before the first code is resolved. The 80 hour window should be long enough to prevent operators from applying temporary remedies, but not so long that operators are unfairly held to the schedule for a past fault condition when a new fault occurs. This repeat fault provision would prevent operators from circumventing requirements by not properly addressing the problem.

As discussed in Section IV.C, EPA is seeking comment on whether improvements could be made to OBD to monitor inducement conditions to ensure a false inducement did not occur and to track such inducements and the conditions that trigger them. Having access to additional OBD data for inducement-related conditions can help operators and repair technicians pinpoint and respond to conditions that currently are often leading to reports of `no trouble found' or false inducements.

As noted in ANPR comments, vehicle operators have experienced inducements that do not seem to be keyed to detected fault conditions, and inducements have occurred on a different schedule than anticipated. These problems may be caused by wear conditions, malfunctioning components, or inadequate system logic. Successful implementation of the proposed inducement provisions depends on production of engines that operate according to the engine manufacturers' designs over a lifetime of in-use operation.

We believe this proposed approach minimizes potential adverse impacts on operators while meeting the fundamental objective that manufacturers design engines to ensure that operators maintain an adequate supply of DEF to keep the SCR emission control system functioning properly.

5. Requests for Comment

We are open to considering a wide range of adjustments to the proposed inducement provisions and request comment on all aspects of the proposal described in this section. We ask that commenters suggesting alternative approaches or specifications consider the principles identified in Section IV.D.3 to inform our development of the proposed provisions. We are interested in any alternative regulatory provisions and any different principles recommended by commenters, as well as commenters' views on how EPA applied the identified principles in developing the proposed inducement provisions.

We are also interested in whether commenters support adoption of inducement provisions that closely follow existing inducement strategies in-use, for example derating to 5 miles per hour within four hours of detecting certain fault conditions and, if so, whether such an approach would meet the principles we described or whether there are other principles that support such an approach.

While we believe the proposed derate schedule would effectively lead every vehicle owner to address certain detected fault conditions within the duration of the specified schedule, we invite comment and relevant information that would help to assess how vehicle operators in a wide variety of vehicle applications would respond to a derate at any specific level of operating speed restriction. Toward that end, we ask for comments in response to the following questions:

• Is the proposed initial speed restriction of 50 (for low-speed vehicles) and 65 miles per hour (for high-speed vehicles) immediately upon detecting a fault condition meaningful? For example, we may consider alternative initial speed restrictions of 40 and 55 mph to focus the operator's attention on addressing the fault condition since the remedy could be as simple as adding DEF or as extensive as making substantial repairs after a thorough diagnosis.
• Is the proposed final speed restriction of 35 (for low-speed vehicles) and 50 miles per hour (for high-speed vehicles) meaningful? For example, we may consider alternative final speed restrictions of 25 and 40 mph.
• Is it appropriate to create a fault condition that triggers inducement three hours before the DEF supply will be depleted? The engine could alternatively be designed to warn the operator when DEF supply is running low and start the inducement when the DEF supply is depleted.
• Is the proposed six hours of non-idle operation the right amount of time for the first stage of inducement to take effect at 50 or 65 miles per hour before progressing to the next stage of derating? A shorter time may be appropriate for simply refilling DEF, but in other situations that may frequently occur, the fault condition causing the inducement requires diagnosing and repairing a defective component.
• Is the proposed schedule for successive derates after 12 and 60 hours appropriate? We may consider additional steps. As an example, we may also consider a longer schedule involving more time between stages such as 20 and 120 hours. Similarly, we may consider a shorter schedule reducing the time between stages such as 8 and 40 hours.
• Is the proposed 80 hours of operation without repeating a fault condition the appropriate length of time to distinguish between a new fault condition that restarts the inducement schedule at the initial derate speed and a repeated fault condition that resumes the previous inducement at the same point that the system deactivated the derate?
• Is the proposed schedule of derating speeds over time for high-speed vehicles from 65 to 50 miles per hour and from 50 to 35 miles per hour both reasonable and effective? Would a more or less aggressive schedule work to prevent operators from being content with restricted operation to avoid the cost or inconvenience of maintaining SCR systems? We request that commenters also explain whether any information provided would support an adjusted schedule consistent with the principles described in Section IV.D.3.
• Is the proposed average speed of 20 miles per hour over the preceding 30 hours of operation the appropriate threshold speed for a more restrictive derate schedule for low-speed vehicles? Is it appropriate to exclude idle from the low-speed vehicle determination?
• Should a high-speed vehicle that continues to operate at the final inducement speed eventually be treated like a low-speed vehicle if its average speed eventually falls to that level (20 miles per hour) based on its slower operation during inducement? Using the proposed values, this would cause a vehicle to eventually shift from a final inducement speed of 50 miles per hour down to a final inducement speed of 35 miles per hour. This question is fundamentally about whether there are any applications or scenarios for high-speed vehicles for which an inducement at 50 miles per hour (or another final inducement speed for high-speed vehicles in the final rule) is insufficient to compel corrective action.
• Monitoring for tampering due to a blocked DEF line or injector is intended to ensure that the line itself is not crimped or the injector plugged intentionally. However, EPA is aware that urea crystallization can mimic this type of tampering. OEMs can monitor DEF line and injector pressures and know at what point they consider pressure changes to be indicative of tampering. They should be able to use these pressure readings to indicate that the system is plugging over time and warn operators well in advance of an inducement (see section IV.C.1.iii.2. for more information on this proposal). If practical, should we specify the amount of time that manufacturers should provide operators with advance notice of a blocked DEF line or dosing valve prior to an inducement occurring for those cases where the blockage is caused by plugging due to DEF crystallization as opposed to direct tampering?

We request comment on the proposed set of fault conditions for triggering inducements intended to address the unique aspect of SCR systems that depend on cooperation from vehicle operators. Toward that end, we raise the following questions:

• Is it necessary and appropriate to include DEF concentration as a fault condition, as proposed? There is an established practice of using DEF and engines now have built-in features to prevent diluting DEF or filling DEF tanks with water. Also, with the proposed warranty provisions, owners may be more likely to properly maintain their engines over longer periods, including use of DEF that meets the owner's manual specifications. We request comment on whether this concern about DEF quality continues to justify the additional complexity and the associated risk of false inducements.
• Are the proposed fault conditions of DEF fill level, DEF quality, and tampering associated with the SCR system the proper way to ensure an adequate supply of quality DEF in-use?

• Does the proposal properly define tampering conditions for inducement by identifying conditions that owners can control, such as open-circuit faults for disconnected DEF pump, SCR wiring harness, DEF dosing valve, DEF quality sensors, DEF tank heaters, DEF level sensors, aftertreatment control module, and NO_X sensors?

• Is there a risk that the engine will incorrectly detect a tampering fault condition based on the specified open-circuit faults? For example, how likely is it that maintenance steps that require disconnecting or disassembling certain components as part of a repair will be identified as tampering? Or, how likely is it that a failing sensor will give an incorrect signal indicating that one of the specified components has been disconnected? The proposal addresses this, at least in part, by including an override feature based on measured NO_X emissions before and after the SCR catalyst.

• Should we allow or require additional fault conditions to ensure that SCR systems are working properly? We could identify numerous additional fault conditions based on OBD system monitoring that detects any number of SCR-related components that need to be adjusted or replaced. We have focused the proposal on things that owners can actually control consistent with the original focus of the existing guidance on ensuring an adequate supply of high-quality DEF paired with tamper-resistant SCR systems that focus on open-circuit conditions. We request comment on any additional OBD fault conditions that would be needed to ensure the functionality of the SCR system.
• Should EPA codify the DEF freeze protection guidance that describes how to meet EPA AECD requirements currently described in CD-13-13?
• Should EPA establish an acceptable range of DEF concentration for defining the limits of the inducement fault condition? Inducements for DEF quality are based on the change in urea concentration from 32.5 percent (unadulterated DEF) to the point at which poor DEF quality can be detected and inducements are triggered. Manufacturers design some tolerance into their SCR systems to adapt to and compensate for in-use DEF quality variances instead of triggering an inducement for minor concentration differences. For example, if a vehicle with DEF in the tank has not been driven for some time, some of the water in the DEF can evaporate, leaving a slightly higher concentration of urea in the DEF. We seek comment on the need to clarify in the regulations appropriate DEF quality inducement triggers to ensure that an acceptable tolerance is being designed into SCR systems consistently across manufacturers and that reflects real-world conditions. Further we seek comment on what an acceptable tolerance would be.

The proposed approach for overriding inducements based on NO_X sensors showing that the SCR catalyst is working properly is an important feature to reduce the risk of false inducements. Operators would see a warning for a fault condition even if the override prevents a speed restriction, which should allow the operator to take the time necessary to address the fault condition. The override should be set at a level of NO_X conversion efficiency to reliably indicate that an override is appropriate because the detected fault condition in fact does not prevent the SCR catalyst from working according to design. We request comment on the proposed approach that allows for overriding inducement if the average data from the NO_X sensor show that the catalyst is reducing NO_X emissions consistent with stored OBD REAL Bin data within an estimated 10 percent margin of error due to limitations of in-use detection and measurement. Toward that end, we raise the following questions:

• Should the margin of error be more or less than 10 percent? NO_X conversion efficiency is more stable at higher speed and load conditions and is generally greater than 90 percent, so overriding based on a greater margin of error should still be effective. Fault conditions such as depleted DEF or disconnected aftertreatment would cause NO_X conversion efficiency to be at or near zero and would quickly impact the NO_X conversion efficiency value due to the stored data array being reset at the time a trigger is detected. In such cases a less rigorous or stringent threshold value would be sufficient to evaluate the validity of the detected fault condition. Note however that some system defects may allow for partial NO_X conversion.

• Are the (reset) Active 100 Hour Array and the specified Real Bins 13 and 14 the appropriate data to assess the NO_X override, as proposed? The selected operating conditions are intended to be most favorable for a stable and repeatable current assessment of NO_X conversion efficiency. Would the NO_X override need to account for a wider range of vehicle operation to work properly for the full range of vehicle applications?

• Does the proposed final inducement speed in combination with the provision for NO_X overrides provide a proper self-healing path for deactivating derates after correcting a fault condition? There are likely times when this may be a preferrable option for operators for resolving an inducement instead of relying on scan tools.

EPA is seeking comment on provisions to accommodate equivalent engine families that are identical except for the diagnostic system adjustments needed to meet the different inducement protocols. If finalized, we would count two equivalent engine families as one for the purposes of determining the number of engine families that are subject to OBD demonstration testing requirements for certification. This would be analogous to the way we are proposing to treat engine families that have a California-only federal certificate because of differences such as warranty provisions (see Section IV.C.2.i.a. for further discussion on this provision).

As described in Section IV.D.1, engine manufacturers have been producing engines for many years with inducement strategies that align with the potential approaches described in EPA guidance. If we replace the guidance documents with regulatory provisions that include new derating specifications, those specifications could be understood to represent an alternative design strategy for meeting the objectives described in guidance relative to requirements for maintenance specifications and adjustable parameters. It may accordingly be appropriate to allow engine manufacturers to modify earlier model year engines to align with the new regulatory specifications. We are not proposing to change the regulation to address this concern. We are seeking comment on whether and how manufacturers might use field-fix practices under EPA's field fix guidance to modify in-use engines with algorithms that incorporate some or all of the inducement provisions we include in the final rule. For example, this approach could potentially allow engine manufacturers to change the final inducement speed from 5 miles per hour to 50 miles per hour over a 60-hour period.

Engine manufacturers may similarly be interested in modifying engines from the current model year by amending the application for certification. See Section XII.B.3 for additional discussion related to amending applications for certification.

Finally, EPA is seeking comment on whether existing manufacturer inducement strategies are causing certain vocational segments to transition from diesel to gasoline powertrains. For example, one school bus manufacturer introduced gasoline-powered buses in late 2016, which appear to have quickly come to represent nearly 25 percent of sales. Another school bus manufacturer has indicated growing interest in alternative fuel powertrains such as gasoline or propane in response to SCR-related maintenance issues and downtime.

E. Certification Updates

In an effort to better serve the regulated community, EPA has taken a number of important steps to streamline the data collection processes that manufacturers use to apply for annual certificates of conformity from the agency. These streamlining efforts include numerous modifications and enhancements to improve the user experience, minimize manual data submission processes, and eliminate duplication of effort for manufacturers. Beginning with the overall process, EPA has made user-centered design a central theme when developing systems for manufacturers. Engaging manufacturers before and throughout the development process helps reduce incorrect assumptions about their business needs and ensures that systems are end-user tested for viability. We recently transitioned our compliance information system from the Verify System to a new Engines and Vehicles Compliance Information System (EV-CIS). This new platform incorporates manufacturer feedback and includes updates that help manufacturers work more efficiently while minimizing the need for costly fixes which can lead to rework. Although we have made significant progress to improve the certification process, we welcome comments suggesting additional improvements EPA could consider.

F. Durability Testing

EPA regulations require that a heavy-duty engine manufacturer's application for certification include a demonstration that the engines will meet applicable emission standards throughout their regulatory useful life. This is often called the durability demonstration. Manufacturers typically complete this demonstration by following regulatory procedures to calculate a deterioration factor (DF). Deterioration factors are additive or multiplicative adjustments applied to the results from manufacturer testing to quantify the emissions deterioration over useful life.

Currently, a DF is determined directly by aging an engine and exhaust aftertreatment system to useful life on an engine dynamometer. This time-consuming service accumulation process requires manufacturers to commit to product configurations well ahead of their pre-production certification testing to complete the durability testing so EPA can review the test results before issuing the certificate of conformity. Some manufacturers run multiple, staggered durability tests in parallel in case a component failure occurs that may require a complete restart of the aging process.

EPA recognizes that durability testing over a regulatory useful life is a significant undertaking, which can involve more than a full year of continuous engine operation for Heavy HDE to test to the equivalent of the current useful life of 435,000 miles. Manufacturers have been approved, on a case-by-case basis, to age their systems to between 35 and 50 percent of full useful life on an engine dynamometer, and then extrapolate the test results to full useful life. This extrapolation reduces the time to complete the aging process, but data from a test program shared with EPA show that while engine out emissions for SCR-equipped engines were predictable and consistent, actual tailpipe emission levels were higher by the end of useful life when compared to emission levels extrapolated to useful life from service accumulation of 75 or lower percent useful life. In response to the new data indicating DFs generated by manufacturers using service accumulation less than useful life may not be fully representative of useful life deterioration, EPA worked with manufacturers and CARB to address this concern through guidance for MY 2020 and later engines.

In this section, we describe our proposal to migrate and update the DF provisions for heavy-duty highway engines from their current location in 40 CFR 86.004-26(c) and (d) and 86.004-28(c) and (d) to 40 CFR 1036.245 and 1036.246. While the current DF guidance is specific to SCR-equipped engines, we are proposing to update our DF provisions to apply certain aspects of the current DF guidance to all engine families starting in model year 2027. We also propose that manufacturers could optionally use these provisions to determine and verify their deterioration factors for earlier model years. As noted in the following section, we propose to continue the option for Spark-ignition HDE manufacturers to request approval of an accelerated aging DF determination, as is allowed in our current regulations (see 40 CFR 86.004-26(c)(2)), though our proposed provision would extend this option to all primary intended service classes. We are not proposing changes to the existing compliance demonstration provision in 40 CFR 1037.103(c) for evaporative and refueling emission standards. As introduced in Section III.E, our proposal would apply refueling emission standards to incomplete vehicles above 14,000 lb GVWR. Incomplete vehicle manufacturers certifying to the refueling emission standards for the first time under this proposal would have the option to use engineering analyses to demonstrate durability using the same procedures that apply for the evaporative systems on their vehicles today.

In Section IV.F.1, we propose two methods for determining DFs in a new 40 CFR 1036.245, including a new option to bench-age the aftertreatment system to limit the burden of generating a DF over the lengthened useful life periods proposed in Section IV.A.3. We also propose to codify the three DF verification options available to manufacturers in the recent DF guidance. As described in Section IV.F.2, the verification options in a new 40 CFR 1036.246 would confirm the accuracy of the DF values submitted by manufacturers for certification. In Section IV.F.3, we introduce a test program to evaluate a rapid-aging protocol for diesel catalysts that we may consider as an option for CI engine manufacturers to use in their durability demonstration.

We request comment on the proposed options for DF determination and verification, including other options we should consider. We further request comment on whether DF testing of the engine is sufficient for hybrid engines and powertrains, or if we should consider additional testing requirements for manufacturers to demonstrate durability of other key components included in a hybrid configuration ( e.g., battery durability testing).

As described in Section XII.A.8, we are also proposing to allow manufacturers of nonroad engines to use the procedures described in this section to establish deterioration factors based on bench-aged aftertreatment, along with in-use verification testing.

1. Proposed Options for Determining Deterioration Factor

Accurate methods to demonstrate emission durability are key to ensuring certified emission levels represent real world emissions, and the efficiency of those methods is especially important in light of our proposal to lengthen useful life periods. To address these needs, we are proposing to migrate our existing regulatory options and include a new option for heavy-duty highway engine manufacturers to determine DFs for certification. We note that manufacturers apply these deterioration factors to determine whether their engines meet the duty cycle standards. For MY 2031 and later Heavy HDE, we are proposing separate duty cycle standards at an intermediate useful life, and are further proposing that a separate deterioration factor would apply for the intermediate useful life as well.

Consistent with existing regulations, proposed 40 CFR 1036.245 would allow manufacturers to continue the current practice of determining DFs based on engine dynamometer-based aging of the complete engine and aftertreatment system out to regulatory useful life. In addition, under our proposed new DF determination option, manufacturers would be able to perform dynamometer testing of an engine and aftertreatment system to a mileage that is less than regulatory useful life. Manufacturers would then bench age the aftertreatment system to regulatory useful life and combine the aftertreatment system with an engine that represents the engine family. Manufacturers would run the combined engine and bench-aged aftertreatment for at least 100 hours before collecting emission data for determination of the deterioration factor. Under this option, the manufacturer would propose a bench aging procedure and obtain prior approval from the Agency, which could be a bench aging procedure that is established today ( e.g., procedures that apply for light-duty vehicles under 40 CFR part 86, subpart S).

We request comment on the options proposed for DF determination. Specifically, we ask commenters to consider if the proposed new bench-aged aftertreatment option accurately evaluates the durability of the emission-related components in a certified configuration. We are proposing to allow manufacturers to define and seek approval for a less-than-useful life mileage for the dynamometer portion of the bench-aging option. We request comment on the need to define a minimum number of engine hours of dynamometer testing beyond what is required to stabilize the engine before bench-aging the aftertreatment. We note that EPA's bench-aging proposal focuses on deterioration of emission control components. We request comment on including a more comprehensive durability demonstration of the whole engine, such as the recent diesel test procedures from CARB's Omnibus regulation that includes dynamometer-based service accumulation of 2,100 hours or more based on engine class and other factors. We also request comment on whether EPA should prescribe a standardized aging cycle for the dynamometer portion, as was done by CARB in the Omnibus rule. We also request cost and time data corresponding to the current DF procedures, and projections of cost and time for the options proposed in this section at the proposed useful life mileages. As discussed in Section IV.F.3, EPA is currently validating an accelerated aging protocol for heavy-duty diesel engine aftertreatment systems. We expect that if the protocol is validated, manufacturers could choose to use that protocol in lieu of developing their own for approval by EPA.

2. Proposed Options for Verifying Deterioration Factors

In proposed new 40 CFR 1036.246, manufacturers would annually verify an engine family's deterioration factor for each duty cycle until all DFs are verified at 85 percent of useful life. We propose that a manufacturer could request to apply an approved DF to a future model year for that engine family, using the proposed updates to carryover engine data provisions in 40 CFR 1036.235(d), as long as the carryover data includes DF verification results for the production year of that new model year as specified in proposed 40 CFR 1036.246(b). Since emission performance is expected to be stable early in the life of the engine, we are proposing not to require DF verification in the first two calendar years following a DF determination for an engine family. Starting in the third year, manufacturers would verify the DFs using an in-use engine with a mileage at or greater than 35 percent of the useful life for the original model year of that DF determination. Subsequent years after production would increase minimum mileages in 10 percent increments each year. Table IV-14 presents the minimum age we are proposing for each year after a DF is applied. We note that these are minimum values and manufacturers could complete the testing earlier if they recruit higher-mileage vehicles for verification testing. If a manufacturer is unable to find enough test vehicles that meet the mileage specifications, we propose that they would perform the testing using vehicles with the highest available mileage and describe how they would attempt to test properly qualified vehicles for later years. If this occurs in the eighth year, they would continue testing in future years until all tested vehicles have mileage that is at least 85 percent of the engine's useful life.

We include three testing options in our proposed DF verification provisions. For each option, manufacturers would select in-use engines meeting the criteria proposed in 40 CFR 1036.246(c), including the appropriate minimum mileage corresponding to the production year of the engine family. We request comment on the proposed number of engines to test under each of these three DF verification options, as well as the corresponding pass threshold.

In the first verification option, proposed in new 40 CFR 1036.246(d)(1), manufacturers would test at least two in-use engines over all duty cycles with brake-specific emission standards in 40 CFR 1036.104(a) by removing each engine from the vehicle to install it on an engine dynamometer and measure emissions. Manufacturers would determine compliance with the emission standards after applying regeneration adjustment factors to their measured results. We propose that the engine family passes the DF verification if 70 percent or more of the engines tested meet the standards for each pollutant over all duty cycles. If a manufacturer chooses to test two engines under this option, both engines would have to meet the standards. We are proposing that the aftertreatment system, including all the associated wiring, sensors, and related hardware or software be installed on the test engine. We request comment on whether EPA should require approval for hardware or software used in testing that differs from those used for production engines and criteria EPA should consider for that approval.

Under our second proposed verification option in new 40 CFR 1036.246(d)(2), manufacturers would perform the testing on-board the vehicle using a PEMS. Manufacturers would bin and report the emissions following the in-use testing provisions in 40 CFR part 1036, subpart E. Compliance would be determined by comparing emission results to the off-cycle standards for each pollutant for each bin after adjusting for regeneration. We propose the PEMS-based verification would require testing of at least five in-use engines to account for the increased variability of vehicle-level measurement. We also propose that the same 70 percent threshold be used to determine a passing result for this option, which is at least four engines if the manufacturer tests the minimum of five engines. In the event that a DF verification fails under the PEMS option, we propose that a manufacturer could reverse a fail determination and verify the DF using the engine dynamometer option in 40 CFR 1036.246(d)(1).

Our third proposed option to verify DF is to measure NO_X emissions using the vehicle's on-board NO_X measurement system ( i.e., a NO_X sensor) according to 40 CFR 1036.246(d)(3). We expect manufacturers would only choose this option if they have a well-established infrastructure to access on-board data from a large number of vehicles ( e.g., telematics). Manufacturers choosing this option would verify their NO_X measurement system meets 40 CFR 1065.920(b), is functional within 100 seconds of engine starting, and maintains functionality over the entire shift-day. Due to further uncertainty in measurement accuracy, and the fact that fewer pollutants would be monitored with a NO_X sensor, we propose the on-board NO_X measurement system option would require testing 50 percent of the production for that engine family with a 70 percent threshold to pass. Similar to the PEMS option, we propose that a manufacturer could reverse a fail determination and verify the DF using the engine dynamometer option in 40 CFR 1036.246(d)(1).

In the case of a failed result from any of these verification options, we proposed that manufacturers could request approval for a revised DF or retest to determine a new DF, but the affected engine families would not be able to generate emission credits using a DF that failed to pass verification. We propose to allow the manufacturer to continue to certify the engine family for one additional model year using the original deterioration factor to provide time for the manufacturer to change the engine and generate new DFs. We may require manufacturers to certify with revised family emission limits and apply revised DFs to retroactively adjust the family emission limits and recalculate emission credits from previous model years that used the invalidated DF. We note that a DF verification failure may result in an expanded discovery process that could eventually lead to recall under our existing provisions in 40 CFR part 1068, subpart F.

As part of the proposed new DF verification provisions, we include a new 40 CFR 1036.246(c) specifying how to select and prepare engines for testing. We are proposing to allow manufacturers to exclude selected engines from testing if they have not been properly maintained or used and require that the engine must be in a certified configuration, including its original aftertreatment components. Recognizing that manufacturers may schedule maintenance for emission-related components, we request comment on whether restricting engines to those with original components would considerably limit the number of candidate engines for testing.

3. Diesel Aftertreatment Rapid Aging Protocol

As discussed in Section IV.F.1, we are proposing that manufacturers could use engine dynamometer testing for less than full useful life in combination with an accelerated catalyst aging protocol in their demonstration of heavy-duty diesel engine aftertreatment durability through full useful life. EPA has approved accelerated aging protocols for spark-ignition engine manufacturers to apply in their durability demonstrations for many years. While CI engine manufacturers could also propose an accelerated aging protocol for EPA approval, CI engine manufacturers have largely opted to seek EPA approval to use a service accumulation test with reduce mileage and extrapolate to determine their DF.

Other regulatory agencies have promulgated accelerated aging protocols, and we are evaluating how these protocols could apply to our heavy-duty highway engine compliance program. EPA is in the process of validating a protocol that CI engine manufacturers could potentially choose to use in lieu of developing their own protocol as proposed in 40 CFR 1036.245. This validation program for a diesel aftertreatment rapid-aging protocol (DARAP) builds on existing rapid-aging protocols designed for light-duty gasoline vehicles (64 FR 23906, May 4, 1999) and heavy-duty engines.

The objective of this validation program is to artificially recreate the three primary catalytic deterioration processes observed in field-aged aftertreatment components: Thermal aging based on time at high temperature, chemical aging that accounts for poisoning due to fuel and oil contamination, and deposits. The validation program has access to three baseline engines that were field-aged to the current useful life of 435,000 miles. For comparison, we are aging engines and their corresponding aftertreatment systems using our current, engine dynamometer-based durability test procedure. We are also aging the catalyst-based aftertreatment systems using a burner in place of an engine. The validation test plan compares emissions at the following approximate intervals: 0 percent, 25 percent, 50 percent, 75 percent, and 100 percent of the current useful life of 435,000 miles. We include more details of our DARAP test program in a memo to the docket.

The DARAP validation program is currently underway, and we have completed testing of one engine through the current useful life. Our memo to the docket includes a summary of the preliminary validation results from this engine. We will docket complete results from our validation program in a final report for the final rule. If the validation is successful, we would likely include an option for manufacturers to reference this protocol for DF determination and streamline approval under proposed 40 CFR 1036.245(b)(2). We request comment on improvements we should consider for the protocol outlined in our memo to the docket, including whether EPA should prescribe a standardized aging cycle, as was done by CARB in the Omnibus rule, for input to the DARAP. We also request comment on the current proposal to require approval to use DARAP or if EPA should codify this protocol as a test procedure.

G. Averaging, Banking, and Trading

EPA established an averaging, banking, and trading (ABT) program for heavy-duty engines in 1990 (55 FR 30584, July 26, 1990). By offering the opportunity to use ABT credits and additional flexibilities we can design progressively more stringent standards that help meet our emission reduction goals at a faster and more cost-effective pace. In Section III, we show that the proposed standards are feasible without the use of credits. However, we see value in maintaining an ABT program to provide flexibility for manufacturers to spread out their investment and prioritize technology adoption in the applications that make the most sense for their businesses during the transition to meeting new standards. An ABT program is also an important foundation for targeted incentives that we are proposing to encourage manufacturers to adopt advanced technology in advance of required compliance dates.

In Section IV.G.1, we introduce our proposal to continue allowing averaging, banking, and trading of NO_X credits generated against applicable heavy-duty engine NO_X standards. We also propose targeted revisions to the current ABT approach to account for specific aspects of the broader proposed program, which include discontinuing a credit program for HC and PM and new provisions to clarify how FELs apply for additional duty cycles. We recognize that ABT allows manufacturers to use generated emission credits (from engines produced with emission levels below the standards) to produce engines with emission levels above the standards. To limit the production of new engines with higher emissions than the standards, we are proposing restrictions for using emission credits generated in model years 2027 and later that include averaging sets (Section IV.G.2), FEL caps (Section IV.G.3), and limited credit life (Section IV.G.4). We are also proposing that credits generated as early as MY 2024 against current criteria pollutant standards could only be used in MY 2027 and later if they meet proposed requirements for the generation of transitional credits (Sections IV.G.5 and IV.G.6).

The existing ABT provisions that apply for GHG standards in 40 CFR part 1036, subpart H, were adapted for the Phase 1 GHG rulemaking from earlier ABT provisions for HD engines ( i.e., 40 CFR 86.007-15). In this rulemaking and described in this section, we are proposing to revise 40 CFR part 1036, subpart H, to also apply for criteria pollutant standards. We are also proposing a new paragraph at 40 CFR 1036.104(c) to specify how the ABT provisions would apply for MY 2027 and later heavy-duty engines subject to the proposed criteria pollutant standards in 40 CFR 1036.104(a). The proposed interim provision in 40 CFR 1036.150(a)(1) describes how manufacturers could generate credits in MY 2024 through 2026 that could be applied in MY 2027 and later.

We request comment on our proposed revisions to the ABT program. As discussed further below, we are particularly interested in stakeholder feedback on alternative approaches to accounting for multiple standards and duty cycles, as well as our proposed approaches for restricting the use of credits that are generated for use in MY 2027 and later.

1. Multiple Standards and Duty Cycles

Heavy-duty compression-ignition engine manufacturers currently must certify to FTP, SET, and off-cycle standards. Based on FTP and SET test results, CI engine manufacturers participating in the ABT program declare FELs in their application for certification. Spark-ignition engine manufacturers that are only subject to FTP standards may also declare FELs based on the FTP duty cycle testing. An FEL replaces the standard and the manufacturer agrees to meet that FEL whenever the engine is tested over the FTP or SET duty cycle—whether for certification or a selective enforcement audit. The current NTE standards apply in-use whenever a CI engine is operating within the NTE applicability limits and are equal to 1.5 times the FTP and SET standards. The same 1.5 adjustment factor applies to the declared FEL for CI engine manufacturers participating in ABT.

We are not proposing changes to the following aspects of the ABT program currently specified in 40 CFR 86.007-15:

• Allow ABT credits for NO_X

• Calculate NO_X credits based on a single NO_X Family Emission Limit (FEL) for an engine family

• Specify FELs to the same number of decimal places as the applicable standards

• Apply FEL caps for NO_X to constrain maximum values for FELs

• Calculate credits based on the work and miles of the FTP cycle
• Limit credits to four averaging sets corresponding to the four primary intended service classes (detailed in Section IV.G.2)

As discussed in Section III, we are proposing to revise HC and PM standards for heavy-duty engines to levels that are feasible without the use of credits. We are proposing not to allow averaging, banking, or trading for HC (including NO_X +NMHC) or PM for MY 2027 and later engines. This includes not allowing HC and PM emissions credits from prior model years to be used for MY 2027 and later engines. For engines certified to MY 2027 or later standards, manufacturers must demonstrate in their application for certification that they meet the proposed PM, HC, and CO emission standards in 40 CFR 1036.104(a) without using emission credits.

While we continue to consider the FTP duty cycle the appropriate reference cycle for generating NO_X emission credits, we are proposing new provisions to ensure the NO_X emission performance over the FTP is proportionally reflected in the range of cycles that we are proposing for these heavy-duty engines. Specifically, we propose that manufacturers would declare an FEL to apply for the FTP standards and then they would calculate a NO_X FEL for the other applicable cycles by applying an adjustment factor based on their declared FEL_FTP . We propose the adjustment factor be a ratio of the declared NO_X FEL_FTP to the FTP NO_X standard to scale the NO_X FEL of the other duty cycle or off-cycle standards. For example, if a manufacturer declares an FEL_FTP of 30 mg NO_X /hp-hr in MY 2031 for a Heavy HDE, where the proposed NO_X standard is 40 mg/hp-hr, a ratio of 30/40 or 0.75 would be applied to calculate a FEL to replace each NO_X standard that applies for these engines in the proposed 40 CFR 1036.104(a). Specifically, for this example, a Heavy HDE manufacturer would replace the intermediate and full useful life standards for SET, LLC, and the three off-cycle bins with values that are three-quarters of the proposed standards. For an SI engine manufacturer that declares an FEL_FTP of 15 mg NO_X /hp-hr compared to the proposed MY 2031 of 20 mg/hp-hr, a ratio of 15/20 or 0.75 would be applied to the SET duty cycle standard to calculate an FEL_SET . Note that an FEL_FTP can also be higher than the NO_X standard in an ABT program if it is offset by lower-emitting engines in an engine family that generates equivalent or more credits in the averaging set. For an FEL higher than the NO_X standard, the adjustment factor would proportionally increase the emission levels allowed when manufacturers demonstrate compliance over the other applicable cycles.

Under the current and proposed ABT provisions, FELs serve as the emission standards for the engine family for the respective testing. In our proposal, manufacturers would include test results to demonstrate their engines meet the declared and calculated FEL values for all applicable cycles (see proposed 40 CFR 1036.240(a)). CI engine manufacturers participating in ABT would use the FELs calculated for the off-cycle bins to replace the standards in the in-use testing provisions proposed in 1036, subpart E and PEMS-based DF verifications in the proposed 40 CFR 1036.246(2). We expect manufacturers would base their final FEL_FTP for credit generation on their engine family's emission performance on the most challenging cycle. For instance, if a CI engine manufacturer demonstrates NO_X emissions on the FTP that is 25 percent lower than the standard but can only achieve 10 percent lower NO_X emissions for the low load cycle, the declared FEL_FTP would be based on that 10 percent improvement to ensure the proportional FEL_LLC would be met. For the duty cycle standards at intermediate useful life, we are proposing that the DF determination data at the equivalent intermediate useful life mileage serve as a demonstration of emission control performance for certification. For off-cycle standards, we are proposing that manufacturers may attest, rather than demonstrate, that all the engines in the engine family comply with the proposed off-cycle emission standards for all normal operation and use (see the proposed 40 CFR 1036.205(p)) in their application for certification.

Once FEL values are established, credits are calculated based on the FTP duty cycle. We are not proposing substantive revisions to the equation that applies for calculating emission credits in 40 CFR 1036.705, but we are proposing to update the variable names and descriptions to apply for both GHG and criteria pollutant calculations. In Equation IV-1, we reproduce the equation of 40 CFR 1036.705 to emphasize how the FTP duty cycle applies for NO_X credits. Credits are calculated as megagrams ( i.e. , metric tons) based on the emission rate over the FTP cycle. The emission credit calculation represents the emission impact that would occur if an engine operated over the FTP cycle for its full useful life. The difference between the FTP standard and the family limit ( i.e. , FEL for criteria pollutants) is multiplied by a conversion factor that represents the average work performed over the FTP duty cycle to get the per-engine emission rate over the cycle. This value is then multiplied by the production volume of engines in the engine family and the applicable useful life mileage. Credits are calculated at the end of the model year using actual production volumes for the engine family. The credit calculations are submitted to EPA as part of a manufacturer's ABT report (see 40 CFR 1036.730).

Where:

Std_FTP = the FTP duty cycle NO_X emission standard, in mg/hp-hr, that applies for engines not participating in the ABT program

FEL = the engine family's FEL for NO_X, in mg/hp-hr.

Work_FTP = the total integrated horsepower-hour over the FTP duty cycle.

Miles_FTP = the miles of the FTP duty cycle. For Spark-ignition HDE, use 6.3 miles. For Light HDE, Medium HDE, and Heavy HDE, use 6.5 miles.

Volume = the number of engine eligible to participate in the ABT program within the given engine family during the model year, as described in 40 CFR 1036.705(c).

UL = the useful life for the standard that applies for a given engine family, in miles.

2. Averaging Sets

EPA has historically allowed averaging, banking, and trading only within specified “averaging sets” for its heavy-duty engine emission standards. This restriction is in place to avoid creating unfair competitive advantages or environmental risks due to credit inconsistency. We propose to continue this approach, using engine averaging sets that correspond to the four primary intended service classes, namely:

• Spark-ignition HDE
• Light HDE
• Medium HDE
• Heavy HDE

As discussed in Section IV.I, we are proposing that manufacturers could certify battery-electric and fuel cell electric vehicles to generate NO_X emission credits. Manufacturers would include battery-electric and fuel cell electric vehicles in an averaging set based on a manufacturer-declared primary intended service class considering the GVWR of the vehicle.

3. FEL Caps

EPA has historically capped FELs for a new criteria pollutant standard at the level of the previous emission standard to avoid engine technologies backsliding. FEL caps limit the amount that an individual engine can emit above the level of emission standard when manufacturers choose to use emission credits to comply with the standard. Without a FEL cap, manufacturers could choose to use emission credits to produce engines that emit at any numeric level for which they had sufficient credits, whereas, with a FEL cap in place, EPA can constrain the level of emissions from engines that are certified with the use of credits. By setting the FEL cap at the level of the previous emission standard EPA can ensure that all engines must at least maintain the current level of emission control performance.

In this section, we are proposing a new approach to setting FEL caps. We believe FEL caps continue to be critical to avoid backsliding through use of emission credits. Considering our proposal to allow manufacturers to include BEVs or FCEVs in the NO_X ABT program, we believe FEL cap levels below the previous standard are appropriate. The zero-tailpipe emissions performance of BEVs and FCEVs inherently provides the opportunity for manufacturers to generate more credits from these vehicles relative to conventional engines that produce emissions between zero and the level the standard. We believe that lower FEL caps would provide a necessary constraint on allowable emission levels from CI and SI engines that would use NO_X credits generated from BEVs or FCEVs. See Section IV.I for more discussion on our proposal to allow manufacturers to generate NO_X emission credits from BEVs and FCEVs.

As specified in the proposed 40 CFR 1036.104(c)(2), the maximum NO_X FEL_FTP values for model year 2027 through 2030 under proposed Option 1, or model year 2027 and later under proposed Option 2, would be 150 mg/hp-hr, which is consistent with the average NO_X emission levels achieved by recently certified CI engines (see Chapter 3.1.2 of the draft RIA). We believe a cap based on the average NO_X emission levels of recent engines is more appropriate than a cap at the current standard of 0.2 g/hp-hr (200 mg/hp-hr) when considering the potential for manufacturers to apply NO_X credits generated from electric vehicles for the first time. For MY 2031 and later under Option 1, we propose a consistent 30 mg/hp-hr allowance for each primary intended service class applied to each full useful life standard. For Spark-ignition HDE, Light HDE, and Medium HDE, this proposed allowance would equate to a NO_X FEL_FTP cap of 50 mg/hp-hr compared to the proposed full useful life standard of 20 mg/hp-hr. Heavy HDE would have a separate NO_X FEL_FTP cap of 70 mg/hp-hr compared to the proposed 40 mg/hp-hr full useful life standard. For MY 2031 and later FEL caps under Option 1, we are proposing a 30 mg/hp-hr allowance in lieu of the proposed Option 1 MY 2027 standard of 35 mg/hp-hr for two reasons. First, we do not believe a 15 mg/hp-hr differential between the MY 2031 and MY 2027 standards would provide an appropriate incentive for Spark-ignition HDE, Light HDE, and Medium HDE manufacturers to develop advanced technologies in early model years. Second, the MY 2031 standard for Heavy HDE is higher than the MY 2027 standard to reflect deterioration over the longer useful life.

We request comment on our proposed FEL caps, including our approach to base the cap for MY 2027 through 2030 under Option 1, or MY 2027 and later under Option 2, on the recent average NO_X emission levels. We request comment on whether the NO_X FEL_FTP cap in MY 2027 should be set at a different value, ranging from the current federal NO_X standard of 205 mg/hp-hr to the 50 mg/hp-hr standard that will be in place for engines subject to CARB's HD Omnibus rule starting in MY 2024. We also request comment on the proposal to set the proposed Option 1 MY 2031 NO_X FEL caps at 30 mg/hp-hr above the full useful life standards. We request comment on whether different FEL caps should be considered if we finalize standards other than those proposed ( i.e., within the range between the standards of proposed Options 1 and 2 as described in the feasibility analysis of Section III).

4. Credit Life for Credits Generated for Use in MY 2027 and Later

In the original heavy-duty criteria pollutant ABT program (55 FR 30584, July 26, 1990), the recent Phase 2 heavy-duty GHG rulemaking (81 FR 73638, October 25, 2016), and the current CARB HD Omnibus rulemaking, a limited credit life was adopted to help encourage continued technology development to meet the proposed standards. We are proposing to update the existing credit life provisions in 40 CFR 1036.740(d) to apply for both CO₂ and NO_X credits. As specified in the proposed 40 CFR 1036.740(d), NO_X emission credits generated for use in MY 2027 and later could be used for five model years after the year in which they are generated.⁶⁶⁴ For example, credits generated in model year 2025 could be used to demonstrate compliance with emission standards through model year 2030.

We are not proposing an expiration date for the ABT program, and manufacturers could continue to generate credits by adopting increasingly advanced technologies. However, we do not see a need for manufacturers to bank credits generated in a given model year indefinitely. We recognize the need to allow enough time for manufacturers to apply credits generated early to cover the transition to the more stringent standards of proposed Option 1 for MY 2031. We believe a five-year credit life adequately covers a transition period for that option, while continuing to encourage technology development in later years. We are not proposing to migrate 40 CFR 86.004-15(c)(1)(ii) that specifies a discount for credits that are banked or traded. Discounted credits were originally included to incentivize manufacturers to adopt new technology instead of relying on the use of older credits (62 FR 54703, October 21, 1997). We believe the proposed five-year credit life would provide the same incentive as a credit discount. We request comment on our proposed five-year credit life.