And yet the total mileage driven by a huge variety of autonomous systems over research programmes dating back a decade is of the order of 20-30 million. This disparity obviously supports my point about the difficulty of establishing statistically significant evidence that a particular software update on a particular platform is less lethal than the human driver [in a given set of circumstances] based on events which are very rare on a per mile basis, particularly if the baseline performance gap isn't that large.

The fact that overall road use is so high that a sufficiently bad regression bug in sufficiently widely-deployed software could rack up a massive body count within hours obviously doesn't make the case for introducing something believed to only be a marginal improvement any stronger.