Fair enough, though I'm more concerned about the claims for fully autonomous vehicles without driver controls. How many times in those billion miles did a human driver intervene? Or rather, would it have been two billion miles on autopilot if the human driver had not had to take control?
Key point is that the autopilot will get better over time, while the humans will not. This is one of those questions that is best answered by looking at the first derivative rather than the quantity in question.
