Comment by Veedrac

This is one of these sets of information that don't seem to make sense until you fit it all together.

Busses aren't much more efficient when riding down a lane than lower occupancy vehicles, but streets aren't bottlenecked by their roads, they're bottlenecked by their intersections. The key advantage of a bus is at the intersection. A bus holds the intersection for far less time than the equivalent passenger capacity of cars.

The problem bus lanes try to solve is dominantly that without them the traffic advantage of people riding busses mostly goes to people not riding busses, and this makes for a pretty terrible incentive structure. Busses are intrinsically disadvantaged against cars (schedules, uncertainty, routes), so if you don't help them, then people will prefer to drive. Bus lanes internalize the externality.