This is a whole new discussion but I'll still give some pointers.

If you consider a city as a whole it would probably be much safer to take all cars off the street and put buses in their place. Less vehicles + trained drivers + less drunk driving => less accidents.

But even considering the normal city with lots of cars, I consider buses safer because: * they usually drive slower * they are big and heavy, so even in the case that a bus collides with a car it will probably be safer in the bus. Ok, if you have a collision against another bus it is another question. * btw, there are buses with seat-belts.