Statistically, self-driving cars are about to kill someone. What happens next?

That's the number of miles, on average, that it takes a human driver to kill someone in the United States. It's also the number of miles Tesla's semi-autonomous'Autopilot' feature had racked up by May this year. Assuming Autopilot is rolled out to Tesla's mass-market Model 3 in 2017, that number will rapidly climb into the billions. Mercedes are deploying similar systems in their new E-class, while Google's fully driverless cars have racked up another 1.6 million miles and counting . As the miles grow, the odds shrink.