Earlier quoted context omitted.
Most people own cars. One the anticipated benefits of self-driving cars is that they can be shared rather than owned. If they are shared they can be constantly in use rather than parked and when parked do not need to be parked where they were last used.
Why are self-driving cars more easily or more likely shared than human-driven cars? Someone else pointed out that they cost less to operate, but I wonder how much will change. People like owning things, including nice cars.
Car ownership requires at worst 1 car per person.
Carpooling requires a lot of planning and only works for with individuals with similar scheduled routes and requires the humans to include the time to drop off additional passengers or pass control of the vehicle to another for additional legs of the trip. Totally aside from the logistical nightmare it requires people to trust others with an asset worth thousands or 10s of thousands of dollars.
Imagine you pick 10 people. Getting them all to and from work shopping etc requires 10 cars at worst in the ownership strategy.
Imagine that carpooling might reduce it to 8 or 9. Its extremely likely that a route could be plotted for 3-5 cars to take all to their desired destinations both by moving back and forth for trips that don't coincide and by making slightly longer trips that move multiple parties.
Now imagine that you have the entire population and can match all the rides that coincide and include an entire range of vehicles including buses to get everyone from A to B maybe you can reduce this to 1-2 per commuter.