Unintended consequences - Department Of Transportation division.

It seems that driving high-gas milage vehicles has a downside. The states do not make as much money from the gasoline taxes and their road building/maintenence budgets are hurtin' From the Wall Street Journal:

Fuel-Efficient Cars Dent States' Road Budgets
Cars and trucks are getting more fuel-efficient, and that's good news for drivers. But it's a headache for state highway officials, who depend on gasoline taxes to build and maintain roads.

The Federal Highway Administration estimates that by 2009 the tax receipts that make up most of the federal highway trust fund will be $21 billion shy of what's needed just to maintain existing roads, much less build new roads or add capacity. Trying to compensate for highway-budget shortfalls, a handful of states are exploring other, potentially more lucrative ways to raise highway money.

"In 10 years, we are going to be in an intolerable financial position, and we need to start fixing it now before the problem starts," says James Whitty, manager of an alternative funding project in the Oregon transportation department.

The Oregon program is an interesting one:

In a year-long pilot program overseen by Mr. Whitty, the cars of 260 volunteers were outfitted with Global Positioning Systems and electronic odometers that recorded the number of miles driven. The drivers bought gasoline at specially equipped service stations, where computers on the pumps subtracted the 24-cents-a-gallon gasoline tax and added a 1.2 cent fee for every mile driven.

Very clever -- tax for the actual road useage and not the efficiency of the vehicle.