It's definitely crashes per mile. Unexpected stuff happens all the time on real roads -- black ice, debris, animals, flat tires -- and safety depends upon the driver's or software's ability to deal with them. It's easy for self-driving not to wander into another lane because they're changing the radio, but it's hard for them to deal with situations their designers didn't anticipate.

> For self-driving cars to be safer than human drivers, there is no requirement that the self-driving cars should be better/safer than the best human driver... the self-driving car simply needs to be safer than the majority of humans.

That is true on a whole, but not true for ME. It needs to be safer than ME, not some hypotehtical average person.

Further compounding it:

> For driving skills, 93% of the U.S. sample and 69% of the Swedish sample put themselves in the top 50% [0]

0 - https://en.wikipedia.org/wiki/Illusory_superiority