Typically in cities the biggest constraint on bus frequency is bus congestion at bus stops (and to a lesser extent congestion in bus lanes), not number of buses. To the point where banning cash on buses can meaningfully increase system throughput, as it decreases lag time at bus stops. This can be alleviated with planning where people have to transfer to get anywhere (moving buses out of chokepoints) but in practice people don't like that.

Actually, I suspect this makes self-driving a particularly _bad_ solution for city buses; getting into the bus stops takes some manoeuvring, particularly when there are other buses there.

One place that self-driving buses could be interesting (and indeed there are already a couple of systems like this) is on fully/near-fully segregated lines, where they don't have to deal with human-operated traffic. Another would be small towns, but you're looking at full magic level 5 at that point.

I think a lot of those problems are solvable in principle, although unfortunately it’s probably not practical and incremental enough to actually happen...

I’m envisaging a system of minibuses, either AI-driven or at least dynamically directed by a central control system. People would use a phone app to book journeys; the app would tell them where to get on and where to transfer, and the central control system would optimise the fleet to get everyone where they need to go.

With much smaller buses, and electronic tap-in rather than cash payments, stops should be fast enough that buses can just queue up in order at each stop, hopefully mitigating the parking difficulties you mentioned (modulo breakdowns, medical emergencies, etc). Likewise, if transfers are fast and easy, hopefully they’d be less objectionable to travellers.

Requiring a phone isn’t ideal as it limits accessibility and privacy. There could also be pre-printed tickets, with QR codes that you scan at the bus stop to see the route info.

Why minibuses and not just taxis? I suspect there’s a good balance to be made between efficient road usage (buses) and efficient routing for each traveller (cars).

I’m also envisaging that if this system were to take off, personal cars could be gradually removed from city centres! Again, that makes life easier for the AI vehicles.

This is all pie-in-the-sky stuff, I know; but I do feel like there are ways we could radically improve city transport mostly using existing roads, rather than building new rails or tunnels.