The AASHO Road Test was a multiyear experiment conducted by the American Association of State Highway Officials (AASHO) during the 1950s and is still perhaps the most comprehensive test on trucks and pavement damage. During the tests, trucks with different weights and configurations were driven around a loop until the road was damaged to a certain point. The tests ultimately resulted in 141 crashes and two fatalities.
The report produced an extensive list of equations for describing the data collected from the tests, and from those equations was born the Generalized Fourth Power Law. It’s a rule of thumb for comparing the amount of pavement damage caused by vehicles with different weights, in terms of axle loads:
road damage equation 1
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. Let’s look at some numbers for comparison.
Consider a EV with two axles and a total weight of 2 tons. Assuming an even distribution, each of its axles would bear the weight of 1 ton. Now consider a semitruck with eight axles and a weight of 40 tons – each of its axles would weigh 5 tons. The relative damage done by each axle of the truck can be calculated with the following equation, and comes out to 625 times the damage done by each axel of the sedan.
(5/1)E4 = 625
Considering that the truck has eight axles and the EV has two, the relative damage caused by the entire semitruck would be 625 x (8/2) – 2,500 times that of the sedan.
P.S. - Many heavy truckers cheat and load their trucks to 50 tons. That is why there are weight stations in many parts of the country to catch the offenders and prevent accidents and damage to roads, bridges and tunnels.