I've been thinking about this question, and Angry Bear posted a little about it. I think it's particularly interesting quandary when applied to suburban/urban communities. This post is really just meant to raise questions and drive discussion - rather than offering concrete proposals.
So what if everyone had driverless cars? Would highways work like public interfaces, where cars merged on and linked into one smooth transportation system? Or would traffic coordination just develop out of the technology itself? What if you could send your car places without you even being in it! (Taxi drivers should wouldn't like it.)
Likewise, public transportation systems might benefit as well. If you could send your car back home, then you wouldn't have to deal with parking costs, and people may be more inclined to use the Metro to go to and from work.
I'll probably return to this concept in the future. Just an interesting think to ponder in the field of transportation economics.