What would probably happen is that the price of a car would go up, which means more people will share a car (this would be feaseable with autonomous cars because you can still leave pretty much whenever you need to, and go pretty much where you need to, because you only need to coordinate with any other group of people who happen to need to leave at that time, rather than select the people you want to share a car with and then coordinate when you need to leave).

There is also the alternative that people will move further away from their work, because they can use the commute time -- essentially then, they would leave their homes at the same time, start working and then leave their offices so that they are home again at the same time, which means (assuming everybody lives at different distances from their workplace) that you automatically get a stackering effect.