Autonomous cars, as with any technology we develop, will likely find it's killer application where it makes the most economical sense. They might start out as busses or even truck, and rather than having a driver behind the wheel, you have control centers where one driver might be managing a whole fleet. Eventually, as we change our infrastructure to accommodate further, I wouldn't be surprised if we rely more and more on them (having a fully ordered traffic system). The key to this is time and patience. It might take 50 years before that occurs.