[IshKebab]

That's assuming their rate of improvement is constant and there isn't a long tail of difficulty. But there is. The long tail of difficult driving situations is very very long.

An example from my most recent drive: I drove through a common where cows graze. I doubt a driverless car is programmed to slow down near cows.

The only solution I can see is to whitelist roads and start with the simplest (motorways/highways) then gradually expand to more and more roads. I guess that's kind of what they're doing - suburban America is very easy (although you still have pedestrians and cyclists to deal with unlike motorways), and maybe whitelisting is the cause of the routing complaint.