MIT Technology Review notes a few serious issues with driverless cars - to date they have been used in very constrained environments. Problems tend to get solved, but not overnight. I would image they will first begin to appear in environements created for them - new megacities for example. It should also be noted that cars - with or without drivers - are not a very efficient way to move people around in urban areas.
Many microcar designs came out of post WWII Europe - cheap transportation for a devastated, but rebuilding economy. A few designs, like the Fiat 500A, began before the war but saw production continue afterwards. 127" long, 50" wide and 54" high, 13 horsepower, a top speed of about 50 mph and roughly 40 mpg. The engine is tiny and almost on top of the front wheels giving enormous legroom. It was said seven foot tall drivers could be accomodated.