D.C. Mun. Regs. tit. 24, r. 24-3102
Overhead clearances shall be not less than twenty-two feet (22 ft.).
Overhead clearances at the entrance to or inside of buildings shall be not less than eighteen feet (18 ft.).
If the overhead clearance at an entrance to or inside of a building is less than twenty-two feet (22 ft.), a warning sign shall be erected at a suitable location at each point where the tracks enter the building.
The overhead warning sign required by § 3102.3 shall be located in a way that directs the trainmen's attention to the reduced clearance.
Overhead and side clearances prescribed in this section may be decreased to the extent of a line extending diagonally downward from a point four feet (4 ft.) from the center line of the track twenty-two feet (22 ft.) above the top of the rail to a point eight feet by six inches (8 ft. x 6 in.) from the center line of the track, and the distance of fifteen feet by three inches (15 ft. x 3 in.) above the top of the rail.
For tracks located at the entrance to or inside of buildings with an eighteen foot (18 ft.) overhead and an eight foot (8 ft.) side clearance, the overhead and side clearances may be decreased to the extent of a line extending diagonally downward from a point four feet (4 ft.) from the center line of the track eighteen feet (18 ft.) above the top of the rail, to a point eight feet (8 ft.) from the center line of the track at fourteen feet (14 ft.) above the top of the rail.
The clearances provided in this section shall not apply to the electric wires and equipment required over any for the operation of trains by electric energy; Provided, that the carriers promulgate and enforce rules that prohibit any employee from being on the top of cars while they are being operated under lower clearances as provided in this section.
Canopies at one (1) side track at a freight platform may be constructed at not less than four feet (4 ft.) from the center line of the track; Provided, that the height of the canopies is a least seventeen feet by six inches (17 ft. x 6 in.) above the top of the rail, and that a full clearance of eight feet by six inches (8 ft. x 6 in.) is maintained on the opposite side of the track from the canopy, or that the center of the track to the adjacent track is not less than fourteen feet (14 ft.).
In the Washington Terminal Union Station, shelters that are over platforms used principally for passenger car operation may be constructed at not less than four feet by six inches (4 ft. x 6 in.) from the center line of the track; Provided, that the height is not less than fifteen feet (15 ft.) above the top of the rail and that the railroads promulgate and enforce rules prohibiting employees from riding on the outside of equipment when they are standing above the car floor height.
D.C. Mun. Regs. tit. 24, r. 24-3102