We have dedicated bus lanes where I live, and they don't really work during heavy rush hour, unfortunately, due to merging and turns. For example, most of the time the bus lane needs to be on the right so it can pick people up, so cars turning right will have to cross the bus lane somewhere. The opposite happens if the bus needs to take a left turn, or if another bus is stopped for maintenance or something and overtaking is necessary.

Not to mention a lot of people figure out where the cameras are for the bus lane auto-fines and just dodge them when appropriate, but I guess that's a third world problem.