D.C. Mun. Regs. tit. 18, r. 18-2502
Except as provided in § 2502.7, no single unit vehicle, including any load on the vehicle, shall have an overall length in excess of forty feet (40 ft.), inclusive of the front and rear bumpers.
Except as provided in §§ 2502.3, 2502.4 and 2502.10, no combination of vehicles, including the length of any load on such combination, shall exceed a total overall length of fifty-five feet (55 ft.), inclusive of the extreme front and rear bumpers of the combination.
A semi-trailer (single) when operated in combination with a truck-tractor and when operated on a street, road, highway, or route specified in § 2511 shall not be subject to the limitations specified in §§ 2502.1 and 2502.2; Provided, that the semi-trailer shall not exceed forty-eight feet (48 ft.) in length.
A semi-trailer and a trailer (double) where operated in combination with a truck-tractor and when operated on a route specified in § 2511 shall not be subject to the limitations specified in §§ 2502. 1 and 2502.2; Provided, that each semi-trailer or each trailer operated in this combination shall not exceed twenty-eight feet (28 ft.) in length.
Except as provided in § 2502.6, no combination of vehicles coupled together shall consist of more than two (2) units, except that four (4) units may be coupled together by the double saddle-mount method.
A tractor-trailer combination may consist of three (3) units coupled together when operated on a route specified in § 2511.
A bus, including the length of any load on the vehicle, shall have an overall length not to exceed sixty feet (60 ft.), if travel is restricted to a route approved by the Director.
The limitations on length of vehicles and loads set forth in this section shall not apply to any load upon a pole-trailer operating in the daytime when transporting poles, pipes, or structural materials which cannot be dismembered, nor to vehicles transporting objects at night when required for emergency repair of public utility or public service facilities.
No pole, pipe, or other material exceeding eighty feet (80 ft.) in length shall be transported, either in the daytime or at night, unless a permit has first been obtained as provided for in § 2508.
With respect to night transportation, each vehicle listed under §§ 2502.8 and 2502.9, and the load on that vehicle shall have a sufficient number of clearance markers on both sides and marker lamps upon the extreme ends of any projecting load to clearly mark the dimensions of the load.
Commercial motor vehicles with semi-trailers with a kingpin distance of forty-one feet (41 ft.) or less (measured from the kingpin to the center of the rear axle, if single, or the center of a group of rear axles), shall not be subject to the limitations specified in §§ 2502.1, 2502.2 and 2511.3.
D.C. Mun. Regs. tit. 18, r. 18-2502