3 ms·

I'm not sure why clipping functions are relevant, because the probability of death isn't 100% even for semis hitting pedestrians at highway speeds. It's actuall

I'm not sure why clipping functions are relevant, because the probability of death isn't 100% even for semis hitting pedestrians at highway speeds. It's actually more like 80-90%. There's still quite a bit of long tail for higher speeds beyond that as well. SUVs and other "heavy" consumer vehicles are somewhere in the 75% range at comparable speeds, while sedans are down around 65% mortality. Feel free to find your own numbers, but I'm using [1]. Vehicle weight and size clearly have a significant effect on mortality even at high speeds. However, not all collisions are at highway speed. Most collisions are at relatively low speed, where weight is an even more significant factor in the energy involved. There are tradeoffs you can make between weight contributed by safety equipment (e.g. bumpers), but to a large extent those tradeoffs are mandated by regulations rather than consumers or OEM engineers. [1] https://www.moneygeek.com/insurance/auto/analysis/pedestrian-chance-of-survival/ https://www.moneygeek.com/insurance/auto/analysis/pedestrian... [2] https://www.nber.org/digest/nov11/vehicle-weight-and-automotive-fatalities https://www.nber.org/digest/nov11/vehicle-weight-and-automot...

meatmanek 4y ago
Vehicle mass matters a lot in vehicle-to-vehicle collisions, where the energy and momentum of each vehicle is going to change a lot, but when a car collides with a person, the car's momentum is barely affected, because the car is already significantly more massive than the person. A 20x mass ratio is already practically infinite. In a direct collision between a moving 1000kg car going 10 m/s and a stationary 50kg person, the person will end up moving somewhere between 9.5 m/s (perfectly inelastic collision) and 19.05 m/s (perfectly elastic). The car will end up moving 9.5 m/s (perfectly inelastic) and 9.05 m/s (perfectly elastic). In a direct collision between a moving 10000kg car going 10 m/s and a stationary 50kg person, the person will end up moving 9.95 m/s (perfectly inelastic) and 19.90 m/s (perfectly elastic). The car will end up moving somewhere between 9.95 m/s (perfectly inelastic) and 9.90 m/s (perfectly elastic). Even though we 10x'd the weight of the car, we only increased the velocity of the person after impact by about 5%, and energy imparted on the person by about 10%. I suspect vehicle size (or rather, the size/shape of the front of the vehicle) has way more effect on pedestrian survivability than the weight of the vehicle. SUVs and trucks will impart the force of impact directly to your torso and head, and then subsequently run you over. Sedans hit you in the legs and then roll you over the top of the vehicle.

meatmanek 4y ago

Vehicle mass matters a lot in vehicle-to-vehicle collisions, where the energy and momentum of each vehicle is going to change a lot, but when a car collides with a person, the car's momentum is barely affected, because the car is already significantly more massive than the person. A 20x mass ratio is already practically infinite. In a direct collision between a moving 1000kg car going 10 m/s and a stationary 50kg person, the person will end up moving somewhere between 9.5 m/s (perfectly inelastic collision) and 19.05 m/s (perfectly elastic). The car will end up moving 9.5 m/s (perfectly inelastic) and 9.05 m/s (perfectly elastic). In a direct collision between a moving 10000kg car going 10 m/s and a stationary 50kg person, the person will end up moving 9.95 m/s (perfectly inelastic) and 19.90 m/s (perfectly elastic). The car will end up moving somewhere between 9.95 m/s (perfectly inelastic) and 9.90 m/s (perfectly elastic). Even though we 10x'd the weight of the car, we only increased the velocity of the person after impact by about 5%, and energy imparted on the person by about 10%. I suspect vehicle size (or rather, the size/shape of the front of the vehicle) has way more effect on pedestrian survivability than the weight of the vehicle. SUVs and trucks will impart the force of impact directly to your torso and head, and then subsequently run you over. Sedans hit you in the legs and then roll you over the top of the vehicle.