1991 ADA Standards for Accessible Design

4.2.4.2 Relationship of Maneuvering Clearance to Wheelchair Spaces.

One full unobstructed side of the clear floor or ground space for a wheelchair shall adjoin or overlap an accessible route or adjoin another wheelchair clear floor space. If a clear floor space is located in an alcove or otherwise confined on all or part of three sides, additional maneuvering clearances shall be provided as shown in Fig. 4(d) and (e).

Fig. 4 Minimum Clear Floor Space for Wheelchairs

Fig. 4 Minimum Clear Floor Space for Wheelchairs