Calculating just deaths / DrivingDistance is easy but overly simplifies the complicated comparison between human- vs self-driving. Comparing normalized deaths is not sufficient to persuade real people to choose self-driving over human-driving. Real humans and society take into account many more factors to accurately compare the two driving modes.

Take a hypothetical scenario where self-driving cars reduce deaths by 10x compared to now, but the deaths caused by self-driving cars are all small children and people with darker skin in human-preventable ways (you can imagine if cameras are used why this could happen). I doubt society would accept this tradeoff.

The safer future is to have humans still drive, but be enhanced by computers and cameras that are installed in the car.