Heavy vehicles put exponentially more wear. Especially if the road was not built for having that weight on it. Let's say you build a drive way for a car. You could park a 2 ton car every day for decades with no damage. Yet a massive truck parked once may fuck it up due to it's sheer weight.
that would make sense if roads are built for 5 trips of a car than 1 trip of truck. ( Because car is travelling longer with that one gallon of gallon.)
Is that true though that X cars travelling a mile of road would do less damage than 1 truck traveling on that same road?
The problem is big load, even if for a short amount of time. Just like for bridges. If a bridge can sustain a car a minute, that doesn't necessarily mean that it could sustain a truck once...