Bizarre road conditions, mechanical failures, the percentage of humans who insist on driving old cars or operating their smart cars manually, improbable edge ca

Bizarre road conditions, mechanical failures, the percentage of humans who insist on driving old cars or operating their smart cars manually, improbable edge cases which the software fails to account for ("race conditions"?), illegal drag racing, hackers playing pranks which turn deadly... Probably lots of other scenarios. You'll never eliminate error completely, but I think we'd all be a lot happier if car crashes happened with the frequency of airplane crashes.