Comment by hhmc
4 days ago
> Also worth considering is that, even if higher limits reduce the rate of accidents, accidents at higher speeds are almost universally more severe.
Obviously this is true, and especially important at low speeds, but I wonder how much difference there is between 70 and 80 — I would have assumed they are both typically fatal
The energy is exponential. It takes 30% farther to stop going 80 than it does going 70.
One of my favorite trivia is the scenario that a car going 50 mph sees an obstruction in front and slams on its brakes and stops just in time just tapping it. A car next to him going 70 mph sees the same object, has faster reflexes, and hits his brakes at the exact same spot of the road. He slams into the object at 50 mph.
Just the difference between 70 and 80 is the energy of going almost 40 mph.
> The energy is exponential.
No, kinetic energy is only quadratic in the velocity, E = ½ mv².
https://en.m.wikipedia.org/wiki/Kinetic_energy
You're correct. My wording was off.
Another related pet peeve is when I see cyclists going the wrong way in a bike lane. On a 40 mph road a cyclist has a differential with traffic of 20-25 mph. An accident would be serious by likely non-fatal. When you ride the wrong you you add the speeds and make nearly all collisions fatal.
> The energy is exponential. It takes 30% farther to stop going 80 than it does going 70.
That's when the issue is stopping distance.
The issue on highways is that you have, for example, two cars in the left lane going 55 MPH and a third approaches going 70 MPH. One of the slower cars sees this and moves over but only at the same time as the faster car is changing into the same lane to pass on the right, so now both lanes are blocked, the faster car hits one of them and they're both edged off the road into a stationary object at highway speeds.
Does it matter if they hit the stationary object with significantly more energy? Probably not; dead is dead.
I guess that's theoretically possible, but even in that rare case, people are going to break if they hit someone. Driving too slow causes some accidents but they rarely lead to deaths. AFAIK, driving too slow is such a minor safety issue that no study has been carried out to ascertain exactly how bad it is though.
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Right the energy is exponentially, but I’d claim that fatalities are saturating.