Completely autonomous vehicles (no human assistance whatsoever) will not easily work in big cities where large numbers of pedestrians are common.

The possibility that a vehicle could kill a pedestrian keeps pedestrians off roadways. No vehicle manufacturer would ever permit the programming to allow for the possibility of an autonomous car hitting a pedestrian. So without major changes to infrastructure in cities or dramatically more stringent penalties and enforcement for jaywalking, traffic will not flow because pedestrians will just walk wherever they want regardless of whether or not a car is coming toward them.

The above is probably just one of many unintended social/behavioral consequences to such a big societal change. In addition to the technological challenges facing autonomous vehicles (most of which are already overcome or very close to being overcome), I believe there are significant behavioral and societal changes that will need to be overcome. I don’t think those changes will happen quickly.