> That's really why "miles" is a poor measure. It implies going faster is safer.

A mile is a mile no matter how fast you drive. It means that in a 13mi trip statistically you will have to intervene once regardless of the speed.

> It would be better to list intervention per hour

And this means that if you have a 13mi trip you'll just floor it to reduce the time, and thus the number of interventions per time (hour).

I agree with mentioning road type and other conditions, like weather. You want to know if the system is significantly worse in snow or fog.