3 ms·

> The damages are proportional to the root of the weight No, road damage is proportional to the 4th power of axle weight. So a car that's 50% heavier will do 5

> The damages are proportional to the root of the weight No, road damage is proportional to the 4th power of axle weight. So a car that's 50% heavier will do 5x the damage to the road. (Assuming the same number of axles.)

AlphaWeaver 3y ago
That's an interesting formula - why is it the 4th power of the axle weight?
- claytonwramsey 3y ago
  It's an empirical result, derived from some testing by the US government in the 1950s [1]. [1]: https://en.wikipedia.org/wiki/Fourth_power_law https://en.wikipedia.org/wiki/Fourth_power_law
jjtheblunt 3y ago
How does one get a four in an exponent here? Is there a link to the math? Edit : cool link below, but includes the disclaimer “The accuracy of the law of the fourth power is disputed among experts, since the test results depend on many other factors, such as climatic conditions, in addition to the factors mentioned above.”
onlyrealcuzzo 3y ago
But 5x a very small number is still small. Loaded semis weigh 20-40x a car. That's 160,000x the damage. And as the author points out - it's not going to change much whether the semi is gas or electric. It's the load of the truck that matters.
- riversflow 3y ago
  Loaded semis also have far more axels, so your math is just wrong out the gate. Another factor that I haven't seen addressed is that Passenger vehicles are much more apt to dive on the brakes to stop. My observation is that roads fail first where people are slamming on the brakes.
  - Gare 3y ago
    Max load for trucks in Europe is usually 10 tons per axle. No passenger vehicle comes even near that.
  - michaelt 3y ago
    > My observation is that roads fail first where people are slamming on the brakes. It's possible you're getting deceived here, because the highest wear road surfaces are made from more durable material, and areas where drivers might need to slam on the brakes often have high friction surfaces, which are more wear-prone. So the industrial area where dozens of fully laden 18-wheelers are making sharp turns every day gets paved in the most durable concrete mix possible, the school zone pedestrian crossing approach gets a high-grip sandpaper-like surface, and a few months later it looks like the school zone is getting a lot more wear.
    - riversflow 3y ago
      Highly unlikely given that the observation is relative to the roads in the immediate vicinity. This is very observable on flat off-ramps. the last ~200 feet before the stop at the end of the off ramp will get ruts within a year or two, but the rest of the off ramp is fine and the other side of the road where cars are accelerating is just fine.

AlphaWeaver 3y ago

That's an interesting formula - why is it the 4th power of the axle weight?

claytonwramsey 3y ago
It's an empirical result, derived from some testing by the US government in the 1950s [1]. [1]: https://en.wikipedia.org/wiki/Fourth_power_law https://en.wikipedia.org/wiki/Fourth_power_law

jjtheblunt 3y ago

How does one get a four in an exponent here? Is there a link to the math? Edit : cool link below, but includes the disclaimer “The accuracy of the law of the fourth power is disputed among experts, since the test results depend on many other factors, such as climatic conditions, in addition to the factors mentioned above.”

onlyrealcuzzo 3y ago

But 5x a very small number is still small. Loaded semis weigh 20-40x a car. That's 160,000x the damage. And as the author points out - it's not going to change much whether the semi is gas or electric. It's the load of the truck that matters.

riversflow 3y ago
Loaded semis also have far more axels, so your math is just wrong out the gate. Another factor that I haven't seen addressed is that Passenger vehicles are much more apt to dive on the brakes to stop. My observation is that roads fail first where people are slamming on the brakes.
- Gare 3y ago
  Max load for trucks in Europe is usually 10 tons per axle. No passenger vehicle comes even near that.
- michaelt 3y ago
  > My observation is that roads fail first where people are slamming on the brakes. It's possible you're getting deceived here, because the highest wear road surfaces are made from more durable material, and areas where drivers might need to slam on the brakes often have high friction surfaces, which are more wear-prone. So the industrial area where dozens of fully laden 18-wheelers are making sharp turns every day gets paved in the most durable concrete mix possible, the school zone pedestrian crossing approach gets a high-grip sandpaper-like surface, and a few months later it looks like the school zone is getting a lot more wear.
  - riversflow 3y ago
    Highly unlikely given that the observation is relative to the roads in the immediate vicinity. This is very observable on flat off-ramps. the last ~200 feet before the stop at the end of the off ramp will get ruts within a year or two, but the rest of the off ramp is fine and the other side of the road where cars are accelerating is just fine.