Consider a standard sedan 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.
Considering that the truck has eight axles and the sedan has two, the relative damage caused by the entire semitruck would be 625 x (8/2) -- 2,500 times that of the sedan.
Fairly sure that truckers aren't paying 2500x what passenger vehicles are paying in taxes/fees.
also from the same article:
“The damage due to cars, for practical purposes, when we are designing pavements, is basically zero. It’s not actually zero, but it’s so much smaller -- orders of magnitude smaller -- that we don’t even bother with them,” said Karim Chatti, a civil engineer from Michigan State University in East Lansing.