Arcades shall be bonused only where the zoning lot of a development occupies:
(a) the entire street line of a block and when the arcade extends the full length of such street frontage; or
(b) a portion of the street line of a block and the contiguous zoning lot contains an arcade extending the full length of the street frontage, and no walls are existing where the two arcades abut; or where the contiguous zoning lot is vacant. Such arcade shall be located at the same elevation as the existing arcade.
Arcades may be interrupted by a bonusable open space such as a publicly accessible open area.