Well, I think that there's a human controlling the vehicle is a big part of the problem with each vehicle taking up so much space. If autonomous vehicles were working in unison, arguably:

* traffic problems will be significantly reduced * you won't need traffic lights like they exist today * the vehicles can be reduced in size (double occupancy perhaps); a family can just order a couple cars and have communication between them * streets can be reduced to fewer lanes; possibly one-way because the vehicles can navigate the best route in any case