I also like the idea of making fines for moving violations somewhat proportional to vehicle mass. The danger posed to others by a 150 lb moped pales in comparison to that of a 4500 lb pickup truck. At least in the U.S., a ticket for speeding 50% over the limit through a residential neighborhood is the same for both, for example. Neither is OK, but considering the disparity in the potential for damage and injury to others, imposing equal fines is insane.
A fully loaded semi is 18,000 lbs per axle. A really huge personal vehicle, an F-350, is 4000 lbs per axle. That's 4.5x the weight, 4.5^4=410, so the semi is doing 410x as much damage. There's really no point in trying to tax personal vehicles for road damage when over 99% of the damage is being done by trucks.
Even driven at gross weight, it's doing 5% of the damage per axle of loaded semi. The semi also has 4-5 axles, so it's more like 2% of the damage of the semi.
Mind you, we're talking here about the most damaging personal vehicle loaded to its maximum weight, and the semi is still doing 50x the damage of the personal vehicle. It's reasonable to say that essentially all road damage is done by semis.
That said, this type of tire is a very tiny fraction of the total miles driven on public highways, and so if you're looking for someone to tax based on the costs they create, it's all heavy trucks.
Trucks and permit loads are pretty much the only things that get close.
Beyond the elastic limit, damage is an exponential function of the pavement loading, but only once that certain minimum psf is hit.
For the majority of a highway's loading curve, the damage-per-force is essentially nil. Plastic deformation and serious fatigue only start as you approach the design limits.
It's 99%+ because cars don't do any real wear or damage to pavement from typical use.
I just wonder what would happen if we charged trucks based on weight.
All of which creates overhead in the form of people to be paid, equipment to build/own/maintain, time lost at all stages, the usual political influence problems, jusrisdiction of different areas of road, implementing policy, and corruption. Most of it will end end up as pass through cost to individuals either way as both consumer goods and roadways are deemed essential. It's ultimately a fairness exercise of tax distribution so like most things in the public interest the arena any idea must be fought in is politics.
And yes, consumers will pay regardless, but at least the difference is reflected in the cost of goods. It could very well be that certain local goods are cheaper than imported goods after road costs are properly factored in, which could change how much is imported.
However, this feels a bit regressive since poorer people will pay more of the cost since roads are largely funded by income tax, but that can be accounted for by shifting other taxes. The idea isn't too punish poor people or shipping customers, but to allow the market to work more efficiently.