A country like the US, especially with vast suburban areas, it isn't necessarily a strict dichotomy between public transport and driverless cars. We can have both.
Especially in the west coast, American cities were built to be navigated by cars. Even today, the very fact that carpool lanes in most parts of California are designated for 2 people/car, not 3 implies we already have separate vehicles for each passenger. If we can take advantage of the road infrastructure and cut down on the need to own a car, it will be a huge benefit to lots of people. See how popular ZipCar is, precisely because of this sort of benefit.
Google Transit already offers you choices when you want to go from A to B. It could do the same thing with driverless cars. Want to take one the whole way? That'll be 60 minutes and cost $12.50. Or you can can take the driverless car to the train, which will take you the rest of the way. $7.50, and takes 1h20 minutes.
I know someone who spent some time in one of Japan's smaller prefectures. He hated how all the trains stopped promptly at midnight, making late night things impossible. Something like this would let you take a train there and an automatic car back.
Especially in the west coast, American cities were built to be navigated by cars. Even today, the very fact that carpool lanes in most parts of California are designated for 2 people/car, not 3 implies we already have separate vehicles for each passenger. If we can take advantage of the road infrastructure and cut down on the need to own a car, it will be a huge benefit to lots of people. See how popular ZipCar is, precisely because of this sort of benefit.