> It's clear that having half the casualty rate per distance traveled of the median human driver isn't acceptable.
Even if we optimistically assume no "gotchas" in the statistics [0], distilling performance down to a casualty/injury/accident-rate can still be dangerously reductive, when the have a different distribution of failure-modes which do/don't mesh with our other systems and defenses.
A quick thought experiment to prove the point: Imagine a system which compared to human drivers had only half the rate of accidents... But many of those are because it unpredictably decides to jump the sidewalk curb and kill a targeted pedestrian.
The raw numbers are encouraging, but it represents a risk profile that clashes horribly with our other systems of road design, car design, and what incidents humans are expecting and capable of preventing or recovering-from.
[0] Ex: Automation is only being used on certain subsets of all travel which are the "easier" miles or circumstances than the whole gamut a human would handle.