D.C. Mun. Regs. tit. 24, r. 24-3104
The minimum distance between center lines of parallel main tracks shall be not less than fourteen feet (14 ft.).
In yards, except as prescribed in this section, track centers between parallel tracks shall be not less than fourteen feet (14 ft.).
In congested yard areas where it is not practical to provide fourteen foot (14 ft.) centers between parallel tracks, thirteen feet by six inch (13 ft. x 6 in.) centers between parallel yard tracks shall be permissible.
The center line of any standard gauge track, except a main track or a passing track, parallel and adjacent to a main track or a passing track, shall be at least fifteen feet (15 ft.) from the center line of the main track or passing track; Provided, that where a passing track is adjacent to and on at least fifteen foot (15 ft.) track centers with the main track, any other track may be constructed adjacent to the passing track with the clearance prescribed by federal standards.
Clearance between center lines of parallel team, house, or industrial tracks shall be not less than thirteen feet (13 ft.), except as provided by federal standards.
Center lines of any ladder track with hand-operated switches constructed parallel to any other adjacent track shall have a clearance of not less than eighteen feet (18 ft.) from the center line of the other track, except that parallel ladder tracks with hand-operated switches shall have a clearance between center lines of ladders of not less than nineteen feet (19 ft.).
D.C. Mun. Regs. tit. 24, r. 24-3104