Self driving cars aren't the next stage of public transport; they're a bandaid solution to American urban design. They're still cars, so they still contribute to traffic and increased pavement wear, and I cannot imagine they'd be cheaper at scale than buses for storage/maintenance/cleaning.
A well run public transit system should obviously be cheaper at scale than robotaxis, but the incentives for Waymo (or Uber, or Lyft, etc.) are very different than the city's incentives. It's very possible that in practice private companies can operate more cheaply at scale than buses because they have much higher incentives to reduce costs and increase efficiency.
It's not a bandaid because American urban design isn't going to change substantially. I don't see American cities changing their mind on how they build and where they build.
They won't be better for maintenance but unless Portland can build the state capacity to fund public transport properly this is better than nothing. Plenty of developing countries rely on buses, jitneys, and low footprint vehicles like mopeds for traffic flow because they don't have the state capacity to enforce an urban framework conducive to public transit. Honestly many US states are the same.
> increased pavement wear
That's buses. Even more with electric buses. They are insanely subsidized by public. Robot taxis are vastly cheaper for everyone.
I spent ten years in the trenches of American urban design policy. The best we could do was lose very slightly less quickly. It's not changing. Trains are great, we should build more, and we probably should replace a lot of bus routes by subsidizing rides on Waymo and its ilk. It'll be cheaper and provide better service.