Yeah but a city mile is different to a motorway mile. You could do loads more motorway miles, cause fewer issues to the road and pay more tax than the city driver that's constantly stopping and starting and torquing the road up.

If you want it to be proportional to road damage it needs to scale with the 4th power of vehicle weight and then multiplied per mile. That would make EVs a proper trade off (since they tend to be heavier).

Could it be simplified rather than just per mile? Instead give allowances in vehicle tax. Low medium and high usage kind of thing.

Should also take into account the age of the combustion engine vehicle as it is more likely to be leaking oil which breaks down asphalt