How safe are autonomous cars?

Driving a car is an extremely complex activity -- somehow we manage to control all that technology and keep our eyes on many things going on around us. We manage to do it well enough that there are not many accidents. But how much can we rely on software to control a car? It ought to be smarter, but does that make driving safer? A fatal accident in May 2016 involving a Tesla Motors car on autopilot made it clear that we can't fully trust it yet, even if, as Tesla CEO Elon Musk says, one fatality in 130 million miles of autopilot relates well to one fatality in 94 million miles of conventional driving.