We don’t have a true “user fee” for roads, but our funding policy tries to approximate one. One source of funds for road maintenance is a tax on fuel consumption; the more or less reasonable idea being that the more fuel you’re using, the more wear and tear you are placing on the roads. As fuel efficiency increases, that revenue declines. The Joint Committee on Transportation and Infrastructure Assessment and Solutions was introduced to the concept of a “vehicle mileage tax” (VMT). (See minutes of October 16, 2013 (pdf).)
If fuel efficiency was increasing more or less uniformly for all motorists, the response would be to increase tax per gallon. Sure, you’re “raising taxes” which is scary; but not really. In that situation, you’re just recognizing that you have to increase the ratio to continue to impose the same tax. Just because your vehicle is getting better gas mileage doesn’t mean that it’s doing any less damage-per-mile to the road. But, where there is a disparity in fuel efficiency, altering the ratio would be a tax increase for the less fuel efficient vehicles.
The VMT, on the other hand, would tie the funding to the number of miles traveled by the vehicle. Concerns with that would have to do with making sure some allowance is made for the fact that heavier, more fuel consuming vehicles, cause more wear and tear on the roads; with accommodating a reluctance to GPS or similar technology being imposed by the government for purposes of taxation; and with desires to maintain incentives for people to acquire more fuel efficient vehicles.