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I mentioned this in my comment, but the "AASHO Road Test" gave us something called the Generalized Fourth Power Law. Explained > It’s a rule of thumb for compa

by judge2020 3y ago

I mentioned this in my comment, but the "AASHO Road Test" gave us something called the Generalized Fourth Power Law. Explained > It’s a rule of thumb for comparing the amount of pavement damage caused by vehicles with different weights, in terms of axle loads: > (W1/W2)^4 > In the equation, W1 is the weight of an axle on vehicle 1, which we would compare to W2, the weight of an axle on vehicle 2. For W1 of 4 tons on an axle and W2 of 1 ton on an axle, vehicle 1 does 256 times as much damage to pavement as vehicle 2.

TacticalCoder 3y ago
> For W1 of 4 tons on an axle and W2 of 1 ton on an axle, vehicle 1 does 256 times as much damage to pavement as vehicle 2. OK so take a loaded semi-truck at 40 tons / 80 000 pounds. How much more damage does it do than the 4 tons W1 of your example? How's the road still even there at all after the semi-truck passed on it? The answer is: because even the W1 vehicle at 4 tons cannot even dent that road. Now I'm not saying a 4 tons car is a good thing but honestly 1 ton to 2.5 tons, I don't think it's even possible to measure the tiny damage they do.
- judge2020 3y ago
  Indeed. So while a 4.5 ton vehicle, the Hummer EV, does 25 times as much damage as a 2 ton sedan, a semi truck with 5 tons on each axle does ~625 times as much damage to the road. But 5 tons is not the standard. The federal axel limit is 20,000 pounds, so a fully loaded truck could be doing the same amount of damage to the road as 10,000 sedans. I doubt this is the average axle weight of all semis on the road, though.
- Timshel 3y ago
  You do realize that not all roads are designed to allow for frequent 40t trucks usage (and they should not). So they might not dent a highway but probably not the same for city streets / suburbs and parkings.
coredog64 3y ago
The AASHO test comes up frequently, but there’s an easier way to evaluate this: What’s the internal pressure required to inflate the tires? The higher it is, the smaller the contact patch and the more damage it will inflict on the road. Large trucks are between 80 and 100 PSI, while your typical passenger vehicle is going to be 35 PSI or under.
- ben-schaaf 3y ago
  Road bicycles go over 100PSI. Motor bike tires have a similar pressure to cars.

TacticalCoder 3y ago

> For W1 of 4 tons on an axle and W2 of 1 ton on an axle, vehicle 1 does 256 times as much damage to pavement as vehicle 2. OK so take a loaded semi-truck at 40 tons / 80 000 pounds. How much more damage does it do than the 4 tons W1 of your example? How's the road still even there at all after the semi-truck passed on it? The answer is: because even the W1 vehicle at 4 tons cannot even dent that road. Now I'm not saying a 4 tons car is a good thing but honestly 1 ton to 2.5 tons, I don't think it's even possible to measure the tiny damage they do.

judge2020 3y ago
Indeed. So while a 4.5 ton vehicle, the Hummer EV, does 25 times as much damage as a 2 ton sedan, a semi truck with 5 tons on each axle does ~625 times as much damage to the road. But 5 tons is not the standard. The federal axel limit is 20,000 pounds, so a fully loaded truck could be doing the same amount of damage to the road as 10,000 sedans. I doubt this is the average axle weight of all semis on the road, though.
Timshel 3y ago
You do realize that not all roads are designed to allow for frequent 40t trucks usage (and they should not). So they might not dent a highway but probably not the same for city streets / suburbs and parkings.

coredog64 3y ago

The AASHO test comes up frequently, but there’s an easier way to evaluate this: What’s the internal pressure required to inflate the tires? The higher it is, the smaller the contact patch and the more damage it will inflict on the road. Large trucks are between 80 and 100 PSI, while your typical passenger vehicle is going to be 35 PSI or under.

ben-schaaf 3y ago
Road bicycles go over 100PSI. Motor bike tires have a similar pressure to cars.