That is only going to happen for most people if the economics of car rentals are VEEEEEERRY reasonable. I am not willing to wait 10 minutes for an available vehicle every time I need to go somewhere. People who are dreaming of a day of full automation need to take this into account, because while I don't know how long the average trip by car is, I suspect that it's somewhere in the 15-20 minute range, which is impossible to match even with a fully autonomous driving scheme that can ignore things like stop lights and stop signs.