WASHINGTON (CNN) -- Americans drove 1.4 billion fewer highway miles in April than they did in April 2007, the Department of Transportation said Wednesday.
Americans have driven 20 billion fewer miles overall this year, the Transportation Department says.
That marks the sixth consecutive monthly drop and coincides with record gas prices and an increase in transit ridership, Transportation Secretary Mary Peters said.
April's drop is more than three times larger than the drop from March 2007 to March of this year, which was 400 million fewer highway miles.
Peters said vehicle miles traveled on all public roads for April fell 1.8 percent from April 2007.
Americans have driven nearly 20 billion fewer miles overall this year and nearly 30 billion fewer miles since November, the department said.
Peters expressed concern that the cutbacks have resulted in the collection of fewer taxes on gasoline. Such taxes are funneled to the federal Highway Trust Fund, which gets 18.4 cents per gallon from gasoline and 24.4 cents per gallon from diesel fuel.
"History shows that we're going to continue to see congested roads while gas tax revenues decline even further," she said.
In addition to driving less, Americans are buying smaller vehicles. Peters said sales of midsize SUV dropped 38 percent last month compared with May of last year as Americans increasingly choose to drive cars, the department said.