No - I'm just pointing out that amortization and prepayment of an annual tax bill is largely a solved problem. I was more thinking of a monthly request to pay X

No - I'm just pointing out that amortization and prepayment of an annual tax bill is largely a solved problem. I was more thinking of a monthly request to pay X. It is predicated on the motorist estimating their annual mileage; but if there was a simple mechanism to make adjustments based on deviation from the estimate then I can't imagine it would be too bad.