Rising fuel prices are having a real impact on American driving habits for the first time in decades. Over 40 billion fewer total miles were driven through the first four months of 2008 than over the same period in 2007. In May alone, Americans drove 9.6 billion fewer miles than the previous year.

This constitutes the single largest and most enduring decline in vehicle miles traveled since the U.S. Department of Transportation began keeping statistics on the matter, according to CNNMoney.com. The main avenues of escape from miles driven are trains, buses and bicycles, in addition to an increase in telecommuting, which eliminates the commute altogether.

The primary cause, of course, is the high price of fuel. Whether miles driven will return to previous rates as fuel prices drop is yet unknown, however.

A somewhat unforeseen consequence of the rise in fuel prices and the drop in use has been the decreased tax revenue generated by fuel sales. While the price has gone up, the tax has not, so decreased road use means fewer gallons sold, and less money in government coffers.