>They're already safer than human drivers, with fewer accidents per mile than humans.

The average driver-less car mile is a lot easier than the average human driven mile (driverless cars have far fewer miles handling inclement weather and rush hour traffic in non-grid cities than humans do) and the human average is dragged down by a small subset of the population that behaves badly.

Driver-less cars are not yet safer than typical drivers and this is before you count all the fender benders the early ones caused by violating social norms by behaving too conservatively in traffic.