Clearly, in every world, the modern one and the future driverless one, childless adults in dense urban areas are the people most likely to benefit from a rides-for-hire approach. Families with children and people who live in suburban, exurban, and rural areas will be the people least likely to rely on rides-for-hire.

One interesting (though not, I think, probably overall very likely) scenario is where total car stock increases in a driverless car world because:

1. Childless urban adults use rides-for-hire, but they already used rides-for-hire and already didn't have cars. Meanwhile, they start substituting some amount of their former public transit travel for the new-cheaper rides-for-hire (so more vehicles are needed to serve them).

2. Families with children and suburban, exurban, and rural families purchase driverless cars instead of signing up for rides-for-hire, because rides-for-hire still don't work very well for them. In fact, they purchase more cars, because the driverless cars offer them more utility than their old cars did.

3. Meanwhile, a smaller number of people in relatively dense suburb do go to rides-for-hire and abandon ownership, but there are relatively few of them and the cars in their localities are relatively poorly utilized, so they don't offset the increases in vehicle stock driven by people in groups 1 and 2.

As I said, I don't think that's overall a likely scenario, but I don't think it's an insane one. I'd say 10% chance of coming about.

- it's a toy (like a motorcycle or boat would usually be) or

- it's a business tool (like a sedan owned by a cabdriver or a minivan owned by a deli owner) or

- it's owned by someone who recently moved from a suburb to Manhattan and brought their car along by default (which most of the time, lasts no more than a few months before they learn the transit system, get fed up with parking, and sell the car) or

- they're a law enforcement officer or family member (because LEOs, even personal cars, usually get away with parking murder here, so from a parking perspective, manhattan looks as convenient as a sleepy suburb, to someone driving a car with the right protective LEO markings to ward off tickets)

- more than one of the above