The self driving cars only have to beat the humans.
How many times have you seen distracted drivers lately?
Yacking on the cell phone...
Texting... (4 times more likely to have an accident than a drunk driver.)
Eating a hamburger...
Drunk...
Stoned...
Feeding the kid in the back seat...
Poorly trained...
etc, etc, etc.
Statistically, the google fleet has done pretty well compared to humans.
Google's Self-Driving Cars Are Ridiculously Safe | Big Think