A large gas tax increase, as hudkina suggests, would modify behavior and purchasing choices without creating huge new bureaucracies. It does seem like the least expensive way to cut gas use. However, I would reduce income taxes by an equal amount to make additional gas taxes revenue neutral. If more mass transit and roadbuilding were desired, the decision should be made to take those costs from the general revenue in a deliberative fashion and in competition with other needs such as health care. Otherwise, the additional gas taxes would largely go into a new government black hole of spending whimsy.

Since so much of our fuel is imported, a gas tax would largely amount to an import tax. It could be a back door way of expanding import taxes while reducing income taxes and/or debt that foreigners wouldn't howl about since they already do it themselves.