There have been UK experiments with busway systems as well, in Telford and Runcorn if I recall. Washington, Tyne and Wear has a system IIRC called "bus link" which are short bus only sections of street between adjacient estates that allow buses through but prevent residential areas becomeing rat runs.
Busways can have a role to play but I am wary of them being pushed by monopoly bus operators who are just after public lolly eg First in Bristol when a rail based system would be more apropriate.
The last bunch of car-hating town councillors (summarily ejected at the last poll) spent 10 Million on a guided busway in Edinburgh. An abject waste of money - the bus shudders along as speeds of up to 20MPH. They could have got a load of pikeys in to lay down some private roads for ten grand but oh no, we had to have state of the art training wheels sticking out of the sides of buses - transport consultants - eh? what would we do without them (apart from save loads of time and public money).

And yes I often see buses which are completely empty in Central London. 

.probably drive it for a week then buy something 