[Cthulhu_]

You say reduction in fleet size and whatnot, but I believe that's assuming population remains the same; as it stands, it grows with about 1% per year. That fleet size reduction would need to exceed 1% a year; I don't think that's very likely.

It also implies people are willing to move from owning a car to time sharing a car. That's not likely, because it'll be businesses that will offer it, and they need to make a profit. As it stands, Uber is more expensive than taxis (and they undercut taxis using dank investment monies); take away the driver and replace it with a more expensive car, and I don't think they'd be able to operate cheaper. Plus, traffic comes in peaks, so that fleet would have to be optimized to handle said peaks.

And of course, a large percentage will need (and want) to use it. It's possible if the transport system becomes government owned or it becomes competitive with car ownership, but I don't see that happening. Sci-fi utopias usually don't explain why everything is going as smoothly as it seems; one explanation is that companies are just that awesome and managed to get a cooperative traffic system up and running whilst making automagic cars cheap enough for everyone, another is that the government or some other singular but benevolent organization is in control of all transport and is making sure it's standardized.