Actually fuel it’s a good proxy for that: its use is proportional to mileage and weight

But fuel usage it not proportional to mileage and weight across vehicle classes, and damage is proportional to axle weight to the fourth power.

A diesel sedan might use 1.25 gal for 100 ton-miles, while a tractor trailer might use a third of that (though, to be fair, I thought this would be a bigger delta before I looked).

But then if you look at "Equivalent Single Axle Loads", a tractor trailer is ~2 ESAL while a diesel sedan is ~0.0003 ESAL. So we're talking maybe 0.13 ESAL/gal for the former vs 0.0001 ESAL/gal for the latter.