D.C. Mun. Regs. tit. 24, r. 24-204
Each applicant for a permit to use surface space shall demonstrate to the satisfaction of the Committee that the use to be made of the space will include provisions for the maintenance of a clear, unobstructed passageway not less than ten feet (10 ft.) in width at all points, entirely across the frontage of the property occupied by the applicant, parallel to the line of the street, and generally in the line of pedestrian traffic.
If the Committee finds that usually, or at certain periods during the day or evening, the flow of pedestrian traffic at a location is sufficiently light to permit a passageway narrower than ten feet (10 ft.), a passageway as narrow as six feet (6 ft.) may be approved by the Committee. Approval for the narrower passageway may be given either at all times when the use of surface space is permitted, or for certain specified periods during the time when the use is permitted.
The width of the passageway or passageways approved by the Committee shall be indicated on the permit issued for the use of the surface space, and the space itself shall be marked to define the width of the passageways.
The markings of passageways shall be by one (1) or more painted white lines, each not less than four inches (4 in.) wide; or by other markings as may be required, extending across the total surface space the permittee is authorized to use.
The markings of passageways shall be done by the permittee in accordance with the directions of the Director.
D.C. Mun. Regs. tit. 24, r. 24-204