It’s bizarre that they didn’t just apply this as a universal tax of miles driven for all vehicles. But the dollar amount sounds about right, so my objection is

It’s bizarre that they didn’t just apply this as a universal tax of miles driven for all vehicles. But the dollar amount sounds about right, so my objection is simply “charge the base miles tax to all vehicles and multiply it by the number of tyres on the car”, or set it by “axle weight ^ 4” as top comment notes, or whatever. They can repurpose the gasoline tax as a carbon emissions tax, set to market rates for the carbon credit cost of a tank of gasoline, since we can generally estimate that within enough accuracy for a carbon tax. Still, at least it’s progress towards rational behavior towards vehicles!