How safe should we expect self-driving cars to be?

Uber has reached a settlement with the family of the woman killed by a self-driving Uber car in Arizona. Car equipped with Uber's self driving technology. More people are also starting to think about setting realistic expectations for self-driving cars, the essential question being whether they can be expected to completely avoid fatalities or whether it's good enough that they reduce them. The ethical implications are far-reaching. What makes this question particularly troublesome is that it ties together computing technology with life-and-death consequences.