A purely autonomous road system would make much better use of space than the current system. For instance, you could discard with the notion of fixed lanes on a motorway as the system could nearly instantly allocate lanes on the basis of demand. You'd also be able to do away with curb side parking in urban centres, which would free up more land for commuting.

A train is obviously more still more efficient between fixed points, but self-driving cars are far more economical for less-frequented routes and more convenient for last-mile transit than buses.