I really should go around digging up figures on land use, pollution, and road maintainance as well as construction costs one day because people always bring up that fuel tax and registration fee bit.
Why? A couple of reasons. A few years ago I did search for some numbers on road maintainance costs. In the cheapest jurisdictions, it was over $8000 per lane mile. But that was highways. Put in context, assuming that gasoline cost $3.50 per gallon and that the entire cost of gasoline constituted the fuel tax it would take over 2200 gallons of gasoline per year to pay off one lane-mile. Assuming that you drive a gas guzzler at 15 miles per gallon, over 140 vehicles would have to use that lane-mile in the course of a year to pay off maintainance costs. Sounds reasonable, but ...
I took the extreme case. You can multiply that figure by 6.5 to account for the highest fuel tax being 52 cents per gallon instead of 3.50 per gallon. So you are now up to 910 vehicles per lane-mile per year in the most stingy state (Nevada). Still not too bad.
But after that I just don't have the numbers to figure out what the actual usage would have to be. The $8000 was the lowest costs per lane mile in the state with the poorest maintained roads, and it is by no means typical. I also know that I was rounding down a lot to make the number favour motorists. I don't know what maintainance this figure covers. Does it cover bridges? Does it cover accident clean-up? No idea. What I do know is that it doesn't cover construction costs.
Construction costs of a major road in an urban centre (yes, I know I'm now mixing road types) is in the millions of dollars per lane mile. That's about 100 times higher than the maintaince costs. Again, I wish that I knew what that covered. Does it include re-construction of roads? Does it include the cost of acquiring land? Does it cover buried roads and raised roads? I don't know.
Even so, 910 vehicles per year may cover some roads but it would barely cover other roads. Particularly in rural areas. If real fuel efficency and real maintainance costs bump that up by a factor of 2 or 3, you're in trouble.
There are all sorts of factors that drive up the cost of building and maintaining infrastructure and I'm not confident enough to say that the gas tax covers it. Granted, almost any motorist will say that it does because they would rather say that they are paying the costs while saying that transit users aren't paying the costs. Which is fictitious. IIRC, transit users in this city cover about 70% of the operating costs for public transit. And this city spends a glut of money on low revenue services and routes (like wheel trans and routes in low density areas), while the bulk of people are forced to pay more than their share on revenue generating routes.
I'm sorry for the brain dump there, but I just wanted to demonstrate that the issue is more complex than a one sentence dismissal.