D.C. Mun. Regs. tit. 18, r. 18-2503
The load upon any part of a vehicle operated alone, or the load upon any part of the front vehicle of a combination of vehicles, shall not extend more than three feet (3 ft.) beyond the foremost part of the vehicle or vehicles; and the load upon any part of any vehicle alone, or the load upon any part of the rear vehicle of a combination of vehicles, shall not extend more than six feet (6 ft.) beyond the extreme part of the rear of the vehicle or vehicles.
No vehicle shall be driven or moved on any street or highway unless that vehicle is constructed or loaded to prevent any of its load from dropping, sifting, leaking, or otherwise escaping from the vehicle; Provided, that sand may be dropped for the purpose of securing traction, or water or other substance may be sprinkled on the roadway in cleaning or maintaining the roadway.
The weight of the load carried on any truck, tractor, trailer, or combination of vehicles, shall not exceed the manufacturer's rated load capacity of the truck, tractor, trailer, or combination, and loads carried on such vehicles shall be adequately secured to prevent shifting, toppling, or in any other manner becoming a hazard.
Any tarpaulin or other covering used to protect the load carried on any vehicle shall be securely fastened to prevent its detachment.
No vehicle shall be parked unattended or left standing upon the streets of the District, except while actually being loaded or unloaded, unless the tailgate is closed; Provided, that this subsection shall not apply to vehicles so loaded that a portion of the load extends upon and is supported by the tailgate.
D.C. Mun. Regs. tit. 18, r. 18-2503