Have human reflex’s been updated since the speed limits were set? The distance a car travels in the time it takes for you to see something like a pedestrian while driving, recognize it as a hazard, press the brake pedal, and then for the car itself to respond to your command and stop is one of the primary determinants of a safe speed.

About the only thing on that front that’s changed since the 70s have been improved breaks, but that’s been largely balanced out by heavier vehicles so stopping distance hasn’t been radically improved.

Higher speed still means longer stopping distances, longer distances between vehicles, wider minimum safe curves, shorter reaction times, more energetic collisions, and a larger gap between the speed limit and the maximum possible speed in rain, snow, and fog, which have remained nearly identical since the vehicles of the 50’s.

Vehicle on vehicle collisions have gotten more survivable when things do go wrong, but surely we should rejoice that people are more likely to survive a trip rather than increasing speeds until just as many die as they did before? I mean personally I would much rather live to see my destination than save a few minutes.

This also all just talking about highways, on all other streets and roads the six year old running out into the middle of the road has not gotten any more crashworthy than they were in the seventies, and slight reductions in speed have been proven to result in massive increases in pedestrian survivability.