the math changes because the autonomous cars become the public transport. all the cars on the left aren't necessary because they wont sit in a lot all day, they will continue to drive and deliver passengers all day. it creates an option of a private form of public transportation, something that only sort of 'half' exists with uber, since you obviously still have the human driver factor (who requires pay, health insurance, hours off, can be drunk on the job, etc) which makes costs/prices go up. If you can automate the driver, rates fall drastically. if you can make the cars electric, you help the planet. it all works nicely together if everything plays out right.

The math changes for how much storage space for cars is needed, but not how much space is needed for transporting people. Changing a garage to something more useful is not exactly helping traffic jams.