1991 ADA Standards for Accessible Design

4.7.11 Islands.

Any raised islands in crossings shall be cut through level with the street or have curb ramps at both sides and a level area at least 48 in (1220 mm) long between the curb ramps in the part of the island intersected by the crossings (see Fig. 15(a) and (b)).

Fig. 15 Curb Ramps at Marked Crossings