[aidenn0]

> These will be more convenient, but also dramatically more expensive, and _that_ certainly reduces the ownership of things.

Yes making them dramatically more expensive would reduce ownership. I suspect they will be expensive at first, but can't think of any reasons they won't get cheaper with time.

>> the mean number of cars on the road at any given time would seem like it would only go up

> That's orthogonal to the question of level of ownership -- these can both be true simultaneously.

It's not orthogonal, but they aren't completely tied together. Per-car utilization would have to go up for them both to be true.

> And it may even be the case that the number of cars on the road goes down. The idea would be that if these services are convenient enough for more people to forego owning their own vehicle in favor of using a fleet, the economics on a per-trip basis would change: ...

Again this seems to presuppose that self-driving cars will require a significantly higher capital outlay (or perhaps that cities not named "New York" will make parking significantly more burdensome, though that could happen without self-driving cars). If a new self-driving car costs a few thousand more than a non-self driving car, and enough people buy new ones that a thriving used market occurs, the outcome would instead be to move people from "Of course I take transit to work; it's only a bit longer and I can read" towards using cars.