D.C. Mun. Regs. tit. 18, r. 18-2509
No operator of any motor vehicle, trailer, or other cargo-carrying body, whether loaded or empty, which is required to display markings or placards in accordance with regulations of the Department of Public Works or rules of the Hazardous Materials Regulations Board established by DOT Order #1100.11, July 27, 1967 ( 49 C.F.R. 170.1) shall enter any tunnel or any access ramp to a tunnel listed in § 2509.6.
Any Metropolitan Police officer is authorized to require the operator of any vehicle, trailer, or cargo-carrying body referred to in this section to stop prior to entering any tunnel or any access ramp to a tunnel listed in § 2509.6, and to require the operator to proceed by a route which does not lead to the tunnel.
No operator of any tank vehicle or tank trailer used for the transportation of any flammable liquid or any hazardous material, regardless of the quantity being transported, or whether loaded or empty, shall enter any tunnel or any access ramp to a tunnel listed in § 2509.6, nor shall an operator of any empty tank vehicle containing any residue, cutback tar, cement, or any other substance thinned with a flammable liquid enter any tunnel or any access ramp to a tunnel listed in § 2509.6.
A new tank vehicle or tank trailer which has never been used for the transportation of a flammable liquid or a hazardous material may be permitted through a tunnel listed in § 2509.6; Provided, that the vehicle shall be accompanied by an invoice, or other shipping paper, stating that the tank vehicle or tank trailer has never been so used.
For the purposes of this section, the term 'hazardous material," means any material included in the term "explosives and other dangerous articles," as used in Title 18, United States Code, §§ 831 -835.
Vehicles in the categories described in this section are prohibited from entering the following tunnels or any access ramp to these tunnels:
D.C. Mun. Regs. tit. 18, r. 18-2509