Ignoring momentarily the preposterous suggestion that walking costs more per mile than driving (and I have 8 cars — I _love_ them), there are several substantial elephants in the room.

Unless we’re all about to hugely change our working patterns, so that we don’t all require to be transported at the same time, then it’s hard to imagine car utilisation getting anywhere near the suggested figure. I could definitely go to work, and the car head home again so my wife can use it, rather than having it sit outside my office all day, sure — but what about when I then want to go somewhere..?

..Which you think you’ve got a “isn’t it obvious — there’s another car round the corner, just Uber it” type answer to. But you ignore that people don’t take taxis for more than just cost reasons — people _like_ cars, and they very much like to have their own cars with all sorts of specifications and so on.

“Transportation as a service” is just public transport on the road. Sure, it’s got plenty of benefits, but I’m not sure everyone wants to ditch their status symbols just yet. Plus, the logical solution would be not to have multiple makes of car, but only the one, most efficient one. Which would be immensely boring.

So, whilst especially in dense urban settings, there is scope for this to work, I don’t think it is likely to be as you propose.

And all this assumes that truly autonomous driving is not too far away — which many would agree with — but many more would not. There are vast technological hurdles to move from current tech, which is basically active cruise control with lane assist, however Tesla, etc would like to spin it — Volvo has essentially the same system from the same supplier but are more realistic about what it can and should be used for.

Urban environments are hugely difficult to do autonomously, especially without everything else being autonomous as well. Bicycles? Ouch. Pedestrians? Running children over? All quite tricky, and more so because one has to pre-determine the outcome, rather than just letting it happen as it does with a human driver.