11 DCMR C-711.6 states that: 

Except as provided in Subtitle C § 711.11, within twenty feet (20 ft.) of all street lot lines, a driveway other than as described in Subtitle C § 711.5 shall be: 

(a) At least twelve feet (12 ft.) wide for one-way traffic or eighteen feet (18 ft.) wide for two-way traffic; and  

(b) Not more than twenty-four feet (24 ft.) wide. 

The Zoning Regulations offer no criteria for determining the minimum threshold of vehicle use requiring two-way traffic thereby triggering the eighteen foot (18 ft.) width minimum requirement. When such a question arises, applicants are to provide, for review by the Office of Zoning Administration, an evaluation conducted by a Traffic Engineer at the applicant’s expense demonstrating that the proposed driveway width serving the specified number of parking spaces is sufficient.