I can't see that thread, I don't have a Twitter account.

Also, aren't heavy trucks much fewer than regular cars plus don't they have designated routes?

You don't need an account to see a thread: https://nitter.net/ajisuzu1/status/1681123111364620294

Volume does not matter, same with routes. You could probably reduce it to the following, passenger vehicles do no damage to roads. If a road is only driven on my passenger cars it will probably succumb to age/weather damage before weight.

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.

Transportation engineer here.

They are much fewer, and they do tend to have different travel patterns than other vehicles, and there is an equivalent average daily traffic for truck traffic where you convert each truck into a large number of other vehicles.

When you do that, the wear due to truck traffic still absolutely dominates almost always.

The wikipedia article about the 1950s study which only conjectured a fourth power itself says that is widely contested as implausible data fitting.