That's pretty optimistic. Without changes in our development pattern, I don't see much change in car ownership for suburban folk. If every trip is a driving trip, everyone needs their own car. People who can't drive could then have their own cars too. If you're in an area where car-sharing and taxis don't work now, I doubt you'll give up owning your own cars. Hard to predict though. 

Most likely result of improvements in efficiency is more driving, negating the improvement. Any possible space and energy savings of automated cars is pretty minor compared to the savings of moving those trips to transit, biking, or walking. Those technologies obliterate self-driving cars in terms of space and energy,  and we don't have to wait!