We should try new methods of raising revenue and fuel efficiency.
I understand that a retail gas tax is a regressive tax. It is also a political hot potato. Nobody wants to be the one to try to raise this tax. It also doesn't completely target the wasteful behavior that we want to modify. Therefore we should try something different.
One idea is to create a market for more fuel efficient cars by basing the annual registration cost on the fuel efficiency of the vehicle.
Set a mpg standard and charge an extra 1-2 hundred dollars per mile under that standard, then increase the standard on some reasonable timetable like 1 or 2 miles per year. The individual states could experiment with different timetables to get to higher mpg standards
This plan creates an immediate incentive. Most people wouldn't want to pay higher fees and would actively look for more fuel efficient cars. This is different from the cafe goals because those goals could be changed or the timetable could be moved out or the automakers could just say that they can't meet the new standard.
New car buyers would want cars that stayed above the mpg standard and used car buyers would have more cars available closer to the standard. We would also be junking the worst mpg cars at a faster rate.
Of course there would have to be exemptions for various legitimate reasons, but if you wanted to drive that hummer as a status symbol you would just have to pay for wasting fuel.
We could sell this as a wasting resources tax and the only people affected would be the wasters. If we frame more of these increased fees and taxes in a negative way like the "sin" taxes we have on cigarettes and alcohol it would be easier to raise taxes.
Tax the sin not the sinner.
minimal government involvement = maximum market results.