I think having an answer to the question is important, but, frankly, having an answer is more important than the answer itself.
Suppose we could see that driverless cars were 95% less likely to get in accidents. I would hate to see the concept get regulated out of existence, because we, as a society, couldn’t agree on how to place blame in the last 5% of cases.
These numbers might seem outlandish, but looking at the study from Virginia Tech, we can see that the accident rate is lower and the driverless car was at fault in 0% of the cases. Zero. And remember this study was published in January 2016, using even older data. Who knows how much the technology has evolved since then?