While I appreciate your passionate focus on this, and given it is your life's work, you clearly are both familiar and invested, I do want to focus on that 10% going from 55 to 65.
Let's accept that. Yes, there's a convenience thing.
When you mention someone I know dying in a traffic accident (the only person who comes to mind was a family member who died long before I was born, and was on a motorbike w/o a helmet when he hit a slick patch - I think 55 vs 65 was moot in that case) - but when you mention that. If the diff between 65 and 55 is 10%, then, the death would very likely have *not* been prevented by a 55 speed limit.
The 50-100% increase in death rate at 70mph... won't dispute that since that wasn't what this was all about. Does seem a bit odd. In this area, 70 is not that uncommon a highway speed, and I don't think the fatality rate is double that of areas where it is 65mph.
And, yes, I agree traffic laws are a game, and meaningless as enforced. People drive what seems to them to be safe, and usually it is around 65 on highways. Or, yes, higher. Going down 95 there are quite a few stretches of 70mph highway.
It would be interesting to see if statistically people are in fact dying at double (or more, people are likely going 75) the rate on those sections.
I'm interested in you bringing up the Gs of deacceleration. After all, typical highway accident is not going to be a head-on collision w/ another vehicle going 65mph. Or even w/ an immovable obstacle. The ones I've seen in my ~300k miles of driving are usually a vehicle losing control, skidding, losing speed...
I just suspect the lab doesn't quite translate to the road, and despite the deeceleration a vehicle in the lab encounters slamming into a concrete wall, or worse, another vehicle going same speed, vast majority of accidents out there aren't along those lines.
I have no idea what scenario you're contemplating. Plugging in 65mph deaccelerating to 0 in half a second into a handy dandy calculator yields 5.91Gs. 55, 5Gs. 70, 6.36Gs... That actually seems pretty linear to me. 18% increase in speed, 18% increase in deacceleration Gs.
Doesn't seem to require magic air bags, just regular safety features. And actually most crashes I saw involved more time than that. Or involved 2 vehicles in motion striking each other. I guess I can imagine a car that for some insane reason didn't notice everyone stopped ahead and kept plowing into vehicles at 70mph. I suppose that deacceleration, even with the cars being shoved forward, would be over a shorter period. Still seems linear, but, eh, that has to be pretty rare out there...
I accept you have a whole lot more experience in this, I'm just wondering if possibly the real world doesn't quite hit the lab scenarios, most of the time, and that's why we aren't actually experiencing total carnage out there.
And, yeah, that a difference between 65 and 55 might not actually prevent that many more lives even *if* cars were watching us and enforcing the speed limit.
And, yes, I totally agree 100MPH was ridiculously dangerous to themselves and others, and would have fallen under reckless driving regardless of the highway laws.