Spotted...

speaking of time-limited bus lanes why is it that when a car is allowed in a bus lane most people find it perfectly acceptable to use it for undertaking other vehicles at/over the speed limit?

Part of the problem here is that a lot of drivers don't realise that bus lanes are time-limited and don't look at the plates indicating the hours of operation. As a result, bus lanes are often clear even when the other lane is congested.