Fuel efficiency decreases generally relative to the surface area of the front of the vehicle, where road damage increases with the mass of the vehicle. So a long, heavy vehicle like a truck is indeed harder on the road relative to their fuel efficiency.

> I mean, trucks are hardly gas efficient, and aren't most roads maintained (supposedly) via gas taxes?

The gas tax hasn't been increased since 1993 and accounts for less than half of road funding.

Not including externalities--such as road maintenance--distorts the market. Better to capture them all so that different forms of transportation can compete "fairly". That is, without hidden subsidies.

The rationale for taxation has changed over time. We are no longer on the gold standard, so the reasons for taxation are different. But overall the reason for taxation hasn't changed, which is to maintain the demand for the central money supply. This of course is the rationale for sovereign entities with their own money supply like the United States. The rationale for taxes for towns, counties, etc is completely different.

I'm sure Uber will come up with some bullshit reason why they don't have 'trucks' and don't have to pay taxes.

I think there's still an argument that it's not enough, as road wear varies with the 4th power of tire load. Ultimately time is another factor in road wear and breakdown, so utilization rates matter, but on balance freight traffic is subsidized.