Just a quick read makes me think that the issue is as simple as extending the gas tax with a new index rate/ increase every year and doing it for only five to ten years so that we can find a better way. Or improve how it is indexed so that costs are being covered. While there are other means of taxing the use of cars and trucks, like annual fees, mileage based, ETC, one also has to look at the ratio of the cost of implementing and monitoring a new system compared to what you get. Even if the collection potential is higher with a different system, is the cost associated with collecting it higher so that you end up at the same place? The gas tax is in place, and so has that as a benefit.
Like mentioned, gas tax seems like the easiest and perhaps the cheapest way to collect a road "user" fee and frankly, it is pretty fair for the vast majority of the time. Cars like the Volt and Prius should have a fee attached anyway due to the carbon footprint issue and frankly, look at the purchase/ future repair price, maybe they sort of do anyway. Diesel, which heavy trucks use, can be more heavily taxed (it might be anyway) and if there is a big switch to natural gas, then that certainly can be taxed per pound with the same results as taxing gas by the gallon.
Hmm,maybe no better solution has been offered because there isn't one?