"*vulnerable road users*."
No Guy. If the work had addressed vulnerable road users the headline number
would have been even lower than 12 mph.
"*This assumes that the drivers will
not brake*" Yes Guy. Of course it does. That's the point.

"*you're using the formula for V when
it's clearly meant to be applied to delta V*" But of course we're entitled
to assume that delta v is equal to v because it's driver response in most
cases which separate the two.

"*you can't apply this formula to the
average speed*" We agree that this leads to an estimation error, but
the estimation error is always to overestimate the speed from the probability
of death. So the error, if corrected, would make the headline conclusion
smaller. Perhaps 10 or 11 mph instead of 12 mph.

"*The 70% don't speed all the time*"
with a ratio of 1,500:1, it hardly matters if the speeding proportion is
30% or 70%. (and in the free travelling conditions where speed enforcement
has its greatest effects it's usually on the high side) It's still a massive
ratio. 50% of 1,500:1 is still 750:1.