> That seems like a 99% solution, but the farmers or amateur racers who put mileage on their cars outside of public roads might be annoyed by that solution.

They still release pollutants into the atmosphere, though.

The whole point of this taxation change is to account for ongoing electrification. The government are concerned about lost tax revenue from fuel duties and need a new mechanism to fund public roads through taxation by those who use it the most.

It's not just about pollutants.

That's a second-order concern - the view that fuel taxes are effectively road usage charges is already cemented by the fact that "red diesel" (fuel with an added chemical colorant) used in agriculture has a much reduced taxation regime vs regular pump diesel.

Tractors do use the road and as large and heavy vehicles I imagine they do a disproportionate amount of damage. I think tractors are just considered more essential so low fuel tax can be considered a subsidy of sorts.