Momentum = Mass * Speed.

Qualitatively, momentum is the property of an object that causes it to resist changes of velocity (or, in this case, speed). It requires a relatively large force to slow down an object that has relatively large momentum, and a relatively small force to slow down an object that has relatively small momentum.

A 5000 pound SUV is, therefore, five times more deadly than a 1000 pound sports-car traveling at the same speed. A 5000 pound SUV traveling at a "safe" speed of 35 mph in a residential area is just as deadly as as 1000 pound sports-car speeding recklessly down the road at an insane 175mph!

Also, vehicles with greater mass and therefore greater momentum at a given speed take a longer time and distance to stop than vehicles with smaller mass (and therefore momentum). A 1000 pound sports-car traveling 35mph with a breaking force of 7500 Newtons will take about 7 meters and one second to stop, where as a a 5000 pound SUV traveling 35 mph with the same breaking force will require about 35 meters and 5 seconds! The SUV would have to be going 7mph to be able to stop in 7 meters and 1 second. (See below for equations).

Limiting the momentum of a vehicle would address all of these problems. Setting a Momentum limit on a road would, for instance make each car on that road equally likely to kill a pedestrian, should they happen to strike one. The momentum limit on residential roads could then be set to a value such that vehicles are not very likely at all to kill pedestrians, thereby reducing the number of senseless deaths. Notice that a speed limit cannot achieve the same thing. If all cars on the road are traveling with equal momentum, then when two cars collide, equal damage is done to each car (and their passengers), which is, by statistical definition, thee safest arrangement for everyone. Setting a momentum limit would also set the braking time and distance of all vehicles on that road to a constant value (given the same breaking force of each vehicle). We could then evaluate how much distance there is around, say, a blind curve and set the momentum limit around that curve such that any driver would have ample distance to stop should something unforeseen (like children playing, construction, cars pulling out of driveways) be happening there.

Instituting a momentum limit would also encourage people to buy smaller cars, which would have positive impacts on the environment, and save space (more on that later).

DeltaT = (DeltaV*M)/F

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