N.Y.C. Admin. Code § 27-470: § 27-470 Ramps.

Ramps used for the movement of motor vehicles and as required exits need not be enclosed when serving tiers above grade. Such ramps shall have a gradient not exceeding one in seven, with nonslip surfaces. A landing having a minimum dimension of twenty feet shall be provided at the discharge point of all ramps at the street level, within the street line. Where a ramp is also used for the parking of motor vehicles, it shall be considered as a parking tier and may not serve as an exit for the occupants of the structure.