[kevincox]

The biggest problem with most bus systems is that they use the same roads as private traffic. This means that for any individual person taking the car is faster than taking the bus. Of course all of these people who live in car-dependent suburbs already have a car so the additional cost to drive is low and they will get there faster and arguably more comfortable (sure, you can't read a book but you have your own personal environment). The end result is that the roads are full, need constant expansion and no one takes the bus.

Subways on rail are often faster than driving so they tend to be incredibly popular and greatly reduce traffic on the road. But subways on rails are not the only way to ensure that public transit is fast.