[bluGill]

There are a few people who use a car rarely enough that a taxi is cheaper than owning, and if self driving cars eliminate the driver and thus drive down costs a few more people will join that number. However these people generally live someplace where local public transit is good, and parking is expensive.

For the vast majority of suburb dwellers, buying a car will be more cost effective. Most of the costs are the same either way, but you have no need for a profit margin, and you don't pay as much fuel (electrons are still fuel!) to run around empty getting to the next passenger. By owning your own car you can in turn leave your stuff in it just in case. By owning your car you ensure it is there when you want to go as opposed to waiting for one to arrive.