Yes but in cities like LA which are planned around cars the major arteries are 3 lanes in each direction, so you can put up signs saying $200 fine if you use the bus lane, give buses priority at traffic lights, run articulated buses with pre paid tickets and you have buses that operate pretty much like trams ('light rail') at a fraction of the cost. In most European cities this won't work as streets are too narrow to accommodate seperated traffic so you need a combination of congestion charging with streets restricted to public transport and/or expensive tunnels. Trams make sense if you have sections of tunnel in denser parts of the city and grade seperated sections in outer areas; buses can't run in tunnels. They also reduce pollution at street level. Diesel fumes from buses are a significant problem in dense European cities.