With a bus bulb, the point is to save the bus the time needed to merge out of and back into moving traffic, at the cost of temporarily blocking that traffic while making a stop.
With a bus bay, the goal is to not block traffic while the bus is stopped, but at the cost of the time necessary to merge back into flowing traffic.
For example in the Czech Republic, the drivers in the running traffic lane are obliged to enable to the bus to leave the bus stop, but this obligation applies only in built up area.
The Czech technical standards from the 1970s and 1990s (ČSN 73 6425) preferred to build bus bays at all classes of roads, the new version ČSN 73 6425-1 from 2007 prefers bus stops in the running lane within traffic calming concept.
This article related to bus transport is a stub.