In a similar vein it occurred to me this week after seeing very full trains in Bristol due to bus cancellations and unreliability that although we think of road capacity as the main constraint on transport, perhaps we ought to think of driver labour, which skews towards trains and trams. .
You can be sure that at least some of the interest in autonomous vehicles, both on road and rail, is due to this. As far as I know, the only fully autonomous commercial services running so far are a freight line in Australia, taxis in San Francisco, and
DLR▸ and tube, if we count those (they do still have a human ready to take control, so not truly autonomous in the way eg the SF taxis are). I expect I've missed a few but it's probably quite a time till we see driverless lorries and buses on the roads.