> Why? As long as it is better than the median driver the roads are safer.

The intent is to increase miles driven, and the drivers a commercial service can be expected to replace first are professionals, not "median drivers". In practice accident stats are also benchmarked against mean drivers in a world in which serious accidents disproportionately involve inadequate drivers (or conditions Waymo does not deploy in)

Then shouldn’t the comparison be to Uber instead of an ambulance?

Ambulance drivers might be a step too far unless autonomous systems are expected to drive ambulances at high speed and run red lights. But my point is that they really do need to be a lot better than the median driver given their real world operational expectations, and especially significantly better than the mean driver they're being benchmarked against here, who probably loses their license for the bodily injuries they cause...

Well Uber drivers don’t have any special qualifications. That’s kinda the point of Uber. Is there any reason to expect them to be safer than the average driver?

Not being super nervous about being behind the wheel, not showing off their speed to their friends and probably being sober is a starting point

I think we both agree Uber drivers aren't the worst drivers on the road but your assertion is that Uber drivers are professionals and so somehow better drivers than the average. But they aren't. They're actually average drivers. So a self-driving car actually has a very low bar to clear.