Mostly agree with following opinions:
1. You failed to mention another important factor in the gas tax vs. mileage tax consideration: different effects on wear and tear on roads according to the weight of vehicles. Since gas taxes are somewhat dependent on vehicle weight since heavier vehicles get poorer mileage, and heavier vehicles cause greater damage, gas taxes are even more fair compared to mileage taxes.
2. It would have also been appropriate to mention that gas taxes pay for two things: maintenance, and construction. Construction can cause more congestion than it solves, but assuming that construction might actually relieve congestion (which it can do if combined with appropriate land-use regulation), a case could be made that appropriate taxation of vehicles would include a flat fee for licensing a vehicle corresponding with the congestion potential of a vehicle even if it isn't being driven far (a 2 mile trip for groceries can cause congestion at rush hour far beyond a two mile trip at other times). The state of washington voted out a severe progressive tax on vehicle owners that was their registration fee - 2% the value of the vehicle each year. This system was nicely progressive in that it put more of the burden for paying for highways on those with the most ability to pay - people who could afford expensive vehicles. (Other aspects of the WA tax system, especially its reliance on sales taxes instead of incomes taxes, made WA about the most regressive state in the US, however; this status has now been exacerbated by elimination of the 2% vehicle registration fees). But a progressive or a flat tax on car auto ownershiop, plus stronger fuel or even better, carbon taxes (since carbon emissions are a major "sin" that needs to be addressed with "sin" taxes along with other measures) seems the best balance of revenue needs with effects of auto usage.
3. A further important component of a fair whole system of auto taxation is the congestion tax. London's seems to be working rather well, and we await to see how Stockholm's system works once implemented (now help up in courts determining fairness of the bidding process but otherwise scheduled to be implemented this year).
