The equation is:

    A * (W / A) ** 4

So, a 2 ton car is 1 unit of damage; a fully loaded 18 wheeler is 20,000 units. On top of that, we expect a 30 mile/day drive from the car, but more like 300+ from the truck. So, throwing in mileage:

    car = 30 units
    truck = 6 million units

If trucks are just 1% of the vehicles on the road, they'd still be 99.9% of the damage.

Dump trucks are even worse.