How would this result in less cars? People are going to still want their own, for convenience. The shared model may work for some, but that will be made up for by rich parents buying self-driving cars for their small children. Imagine not having to drive your kid to soccer practice, but have a car do it for you... Since there is no need for drivers licenses for those cars, there will be a lot of cars sold for children's use, which will more than make up for those that are using the shared cars.