If they really want to make road taxes usage based, then they need to charge by the ton-mile or something like that. Wear and tear on roads goes by the weight of the vehicle, and if I remember correctly it is a non-linear relationship (square or cube, I can't remember).
It's pretty trivial for a vehicle to compute its own weight, so it is similarly trivial for a vehicle to compute its own road tax as well. Many cars are now coming equipped with GSM modems as well, so your car could simply upload your road impact once/month and you can be billed for your use tax.
Piece of cake.