A semi is doing 400x as much damage as essentially the heaviest personal vehicle driving. For a more typical car at 4000 lbs (2000 lbs per axle), the semi does 6000x as much damage. If semis are 2% of all traffic (true in my observation), they're doing over 99% of the damage to roads. It makes no sense to care about road damage at all from any vehicle other than a heavy truck.