My thoughts are - all self driving cars at the moment operate knowing that there is a human at the wheel, so they are likely to notice a broken suspension coil, rattling clutch, or deflated tyres(even if the sensor reports they are fine, which happens). For "true" autonomous cars the car has to know it itself - especially if it is to allow passangers to literally go to sleep, or even drive without them - so you can summon it from the other side of the city for example. The computer just has to know 100% of its own state, and that requires a huge number of sensors.

Notice how all those miles are in California where it almost never rains. It's still a hard problem, but it's much easier than driving in Alaska or Seattle. When I see millions of accident-free miles from those places, that's whe I'll be truly impressed, even if it's done with adapted infrastructure.