Length and width of bus bulbs varies based on street geometry, vehicle types, and urban context. 30-foot bus bulbs are widely used for non-articulated buses operating two doors. Longer extensions may be required for articulated buses and shorter bulbs may be possible for buses operating a single door. In Portland, Oregon all bus bulbs are 6 feet wide to provide a 2 foot “shy zone” between the bulb and the travel lane.
Kay Fitzpatrick et al., TCRP Report 65: Evaluation of Bus Bulbs (Washington, D.C.: Transportation Research Board, 2001), 5.