Tolls, gasoline taxes, and other user fees cover only about 70% of the direct cash costs of building and maintaining the nation's road system. The rest comes from government subsidies funded by our taxes.

There are hidden costs as well: damage caused by air pollution, increased rates of asthma, the cost of mending people injured in traffic accidents, and the need for strategic involvement with oil-producing nations.

Lester Brown, in his 2009 book, Plan B 4.0, estimated that, if all of the subsidies and the hidden costs were added to the price of gasoline, drivers would need to spend about $12.00 per gallon of gas to pay fully for the cost that car travel imposes on the economy.