Drivers shave off 9.6B miles in May

NEW YORK (CNNMoney.com) -- Americans drove 9.6 billion fewer miles in May compared to a year earlier, according to a report from the Federal Highway Administration.

The decline was the third-largest monthly drop since the agency, a division of the U.S. Department of Transportation that manages the nation's highways and bridges, began collecting data 66 years ago. Three of those largest monthly declines have occurred since December, as unusually high fuel prices take a toll on drivers.

It was the largest drop for any May, a month that usually sees driving increase due to the Memorial Day holiday, the agency said.

Gasoline prices soared in May, rising for 24 consecutive days in the month, and breaking the psychologically significant $4-a-gallon barrier in many states, according to data from motorist group AAA.

As high fuel costs led many to rely on other forms of transportation, such as mass transit, and to cut back their miles on the road this year, the reduced driving also sliced tax revenue that would normally go toward highway maintenance, the highway agency said.

The federal tax on gas generates 18.4 cents per gallon of regular gas sold and 24.4 cents per gallon for diesel fuel, which gets pumped in to the federal Highway Trust Fund. Some states also add a tax of their own to fund various projects. But as Americans drive less, new ways are needed to fund the national road system, the highway agency said.

"We must embrace more sustainable funding sources for highways and bridges through more sustainable and effective ways such as congestion pricing and private activity bonds," warned U.S. Secretary of Transportation Mary Peters in a statement.