Here is an alternative: make the gas tax *regressive*.
The current United States federal excise tax on gasoline is 18.4 cents per gallon and 24.4 cents per gallon for diesel fuel. State taxes vary, see link below.
http://en.wikipedia.org/wiki/Fuel_taxes_in_the_United_States#State_taxes
So say, if gasoline only costs a dollar, the gas taxes are 40 cents on that dollar.
But if the price of gasoline goes up to two dollars a gallon, the *regressive* gasoline taxes drop to 20 cents on the dollar.
If the price of gasoline goes up to three dollars a gallon, the *regressive* gasoline taxes drop to 10 cents.
And at four dollars a gallon, there are NO federal or state gasoline taxes.
Doing it this way will guarantee that politicians continue to strive to keep the price of gasoline and diesel as low as possible.
They have that incentive today. Since the government makes 18.4 cents per gallon independent of the price, the lower the pump price, the more gasoline used, the more the government makes.
A nice thought, but anything that gives them more interest in gaining control over prices is a very very very bad thing.