045-II Wyo. Code R. § 1.2
(1) All of the spot speed data and other information described in this section shall be collected by engineers or technicians who have been properly trained by the Wyoming T2/LTAP Center to collect field data.
(2) The data analysis required to make the final recommendations on setting proper speed limits can be conducted by professional engineers only. Those professional engineers are not required to visit the actual location where the study is being conducted as long as the required data was collected by trained technicians or engineers.
(3) For the engineering studies, vehicle speeds and traffic volumes should be determined using automated traffic counters. Each automated traffic counter should consist of a traffic counter device, two pneumatic tubes, and some additional accessories. The two pneumatic tubes are placed across the road at the recommended spacing. Two ends of the tubes are fixed on the shoulder, while the other two ends are connected to the traffic counter device.
(4) For most low volume unpaved roads, 7 consecutive days of traffic counts are required. For unpaved roads with more than 200 vehicles per day, 2 days of traffic counts may be adequate. Selecting the spot to take speed measurements-the location, traffic, and weather conditions under which to conduct the spot speed study-is generally a matter of common sense. Since average speeds over the length of a section of roadway are the main interest, speed measurements should be taken at the midpoint of a typical section.
The most important aspect of the location is to avoid areas of acceleration and deceleration, such as access points, curves, bad drainage areas, and locations close to roadside hazards. The final layout of the data collection site should be fully described in any report of speed data. The crew should make an accurate sketch of the site, showing the roadway widths and the position of the traffic counters. The crew should record the start time, end time, any downtime, and the conditions prevailing during the study. Such conditions should include a description of any significant road surface distresses. It is essential that speed studies are performed only on roadway segments with average surface conditions.
(5) A special form was developed to assist with the collection and analysis of the traffic count data and the safety aspects of the road as shown in Figure 1-1. The form includes five parts: general information, automated traffic count values, roadway characteristics, historical crash data, and range of speed limit values. In the form, the clear boxes correspond to input that trained technicians or engineers are required to obtain. The gray shaded boxes correspond to the calculations and information that the professional engineer is required to provide. An example of a completed unpaved roads speed limit form is shown in Figure 1-2.
(6) When collecting speed study data, the general information should be completed before proceeding to the next steps.
(7) The required automated traffic count values can be obtained from the output file that the automated traffic counters produce. As shown in Figure 1-3, the output file summarizes the different speed and traffic volumes that the automated traffic counters produce. Four of these values are required in the form and they are: 85th percentile, 50th percentile, the Average Daily Traffic (ADT) and the Average Daily Truck Traffic (ADTT).
Figure 1-1 Unpaved Roads Speed Limit Form
| GENERAL INFORMATION | |
| LOCAL JURISDICTION: | |
| ROUTE: | |
| LOCATION: | |
| DATE: | |
| AUTOMATED TRAFFIC COUNT VALUES | |
| 85th PERCENTILE: | |
| 50th PERCENTILE: | |
| UPPER BOUND OF THE PACE SPEED: | |
| AVERAGE DAILY TRAFFIC: | |
| AVERAGE DAILY TRUCK TRAFFIC: | |
| ROADWAY CHARACTERISTICS | |
| ROADWAY LENGTH: | |
| NUMBER OF ACCESS POINTS: | |
| ACCESS POINTS PER MILE: | |
| ROADWAY WIDTH: | |
| ADJACENT LAND-USE: | |
| TYPE OF TERRAIN: | |
| HISTORICAL CRASH DATA | |
| FATAL: | |
| INJURY: | |
| PDO: | |
| EPDO: | |
| EPDO PER MILE: | |
| RANGE OF SPEED LIMIT (MAXIMUM = 55 MPH) | |
| PREFERRED SPEED LIMIT: | |
| LOWEST ACCEPTABLE SPEED LIMIT: | |
Figure 1-2 Example of a Completed Unpaved Road Speed Limit Form
| GENERAL INFORMATION | |
| LOCAL JURISDICTION: | Smart County |
| ROUTE: | 700 |
| LOCATION: | MP 16.1 to MP 26.1 |
| DATE: | 7/1/2011 |
| AUTOMATED TRAFFIC COUNT VALUES | |
| 85th PERCENTILE: | 43.9 |
| 50th PERCENTILE: | 35.7 |
| UPPER BOUND OF THE PACE SPEED: | 40.4 |
| AVERAGE DAILY TRAFFIC: | 141 |
| AVERAGE DAILY TRUCK TRAFFIC: | 4 |
| ROADWAY CHARACTERISTICS | |
| ROADWAY LENGTH: | 10 |
| NUMBER OF ACCESS POINTS: | 63 |
| ACCESS POINTS PER MILE: | 63 / 10 = 6.3 |
| ROADWAY WIDTH: | 20 |
| ADJACENT LAND-USE: | Recreation/Scenic |
| TYPE OF TERRAIN: | Rolling |
| HISTORICAL CRASH DATA | |
| FATAL: | 0 |
| INJURY: | 5 |
| PDO: | 8 |
| EPDO: | 9.5*0 + 3.5*5 + 8 = 25.5 |
| EPDO PER MILE: | 25.5 / 10 = 2.55 |
| RANGE OF SPEED LIMIT (MAXIMUM = 55 MPH) | |
| PREFERRED SPEED LIMIT: | 43.9 rounded to nearest 5 = 45 |
| LOWEST ACCEPTABLE SPEED LIMIT: | 45 - 10 = 35 |
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(8) Roadway characteristics should be collected during the field inspection of the road The list and description of each characteristic that are included in the form are as follows:
Roadway Length: The length of the road in miles.
Access Points: Total number of access points on the whole roadway length.
Access Points per Mile: Divide the number of access points by the roadway length.
Roadway Width: The total width of the road including both shoulders.
Adjacent Land-Use: Refers to the type of users of the road. The following different types of land-uses were obtained from AASHTO's Guidelines on Geometric Design for Very Low Volume Roads:
. Rural major access roads serve a dual function of providing access to abutting properties as well as providing through or connecting service between other local road or higher type facilities.
. Rural minor access roads serve almost exclusively to provide access to adjacent property. The length of minor access roads is typically short. Because their sole function is to provide access, such roads are used predominantly by familiar drivers.
. Industrial or commercial access roads serve developments that may generate a significant proportion of truck or other heavy vehicle traffic. These roads are classified separately from minor access roads, which they otherwise resemble, because of the consideration for trucks and other heavy vehicles.
. Recreation and scenic roads serve specialized land uses, including parks, tourist attractions, and recreation facilities, such as campsites or boat-launch ramps. Their users are often unfamiliar drivers and serve recreational vehicles including motor homes, campers, and passenger vehicles pulling boats and other trailers.
. Rural resource recovery roads are local roads serving logging or mining operations. Resource recovery roads are distinctly different from the other functional subclasses of very low-volume local roads in that they are used primarily by vehicles involved with the resource recovery activities and the driving population consists primarily or exclusively of professional drivers with large vehicles.
. Rural agriculture roads are used primarily to provide access to fields and farming operations. Vehicle types that use such roads include combines, tractors, trucks that haul agricultural products, and other large and slow-moving vehicles with unique operating characteristics.
Type of Terrain: Refers to the general geometrics of the road. There are three different types of terrain that can be chosen:
. Level
. Rolling
. Mountainous
(9) The historical crash data can be obtained from the safety division of WYDOT or the Wyoming T2/LTAP Center to get the latest crash statistics. It is recommended that 10 years of crash data be included in the evaluation The following three types of crashes are required: number of fatalities, number of injuries, and the number of Property Damage Only (PDO). The Equivalent Property Damage Only (EPDO) is calculated by Equation 1.
EPDO = 9.5 * Fatalities + 3.5 * Injuries + PDO (Equation 1)
Once the EPDO is calculated, the EPDO per mile is determined by dividing the EPDO by the roadway length.
(10) The preferred speed limit is the 85th percentile speed rounded to the nearest 5 mph. The lowest acceptable speed limit may be up to 10 mph less than the preferred speed limit.
045-II Wyo. Code R. § 1.2