2010 ADA Standards for Accessible Design Pocket Guide
503.3 Access Aisle.
Passenger loading zones shall provide access aisles complying with 503 adjacent to the vehicle pull-up space. Access aisles shall adjoin an accessible route and shall not overlap the vehicular way. [S.H. 4.6.6]
Access aisles serving vehicle pull-up spaces shall be 60 inches (1525 mm) wide minimum.
Access aisles shall extend the full length of the vehicle pull-up spaces they serve.
Access aisles shall be marked so as to discourage parking in them.