Benefits include preventing buses from being delayed by having to pull back into traffic, reducing risk of traffic collisions, reducing pedestrian exposure in crosswalks (if provided at the same location), reducing sidewalk congestion, providing space for bus patron amenities including bus shelters, and traffic calming.
The protrusion also facilitates easier full length alignment of a bus entrance with a raised kerb stop, especially to allow level boarding in the case of low-floor buses.
[3][5] Where more than one lane exists in one direction, modelling has shown that there is no additional delay overall for following drivers, since the buses have shorter dwell times (there is less time spent pulling back into traffic) and since following vehicles may use the second lane for passing.
The latter, which operates mostly on traditional streetcar tracks in mixed traffic with cars, and has frequent request stops similar to bus routes, is introducing bulbs at some high-traffic stops and transfer points that have been recently renovated, notably on Roncesvalles Avenue.
The first bulbs (called bumpouts locally) along Roncesvalles Avenue also accommodate cyclists, as the bike lane running parallel to the streetcar tracks would gently rise up from the road level to run on top of the bumpout.