How do you define “safe driving” in terms a machine can understand?

"Bryant Walker Smith, a law professor at the University of South Carolina who studies driverless-car regulations, similarly welcomes the proposals from Mobileye and Voyage, but warns that it is too soon for regulators to “calcify dynamic conversations that are fundamentally technical in nature”.
 

That is because the road-safety debate about autonomous vehicles is driven by emotion, not logic. “If we’re willing to say we’re happy with humans killing themselves on roads, we don’t have a principled basis to regulate AVs,” says Mr Walker Smith, who thinks much more could be done with human drivers to improve road safety: reducing and enforcing speed limits, for example. But the truth is that AVs will always be held to higher safety standards than human drivers."