As gas prices continue to set records, Americans are driving less and using public transit more, a trend that has lasted the past six months.

U.S. Transportation Secretary Mary Peters said that Americans drove 1.4 billion fewer highway miles in April 2008 than April 2007. Vehicle miles on all public roads dropped nearly 2 percent from April 2007 to April 2008. There is a decline of almost 20 billion miles travelled this year.

"We’re burning less fuel as energy costs change driving patterns, steer people toward more fuel-efficient vehicles and encourage more to use transit," Peters said. "Which is exactly why we need a more effective funding source than the gas tax."

Peters said the decrease in driving means a more sustainable and effective way to fund highway construction and maintenance needs to be found. She said that as Americans drive less, the federal Highway Trust Fund receives less revenue from gasoline and diesel sales -- 18.4 cents per gallon and 24.4 cents per gallon, respectively.

Peters said that midsize SUV sales were down last month 38 percent over May 2007, while car sales -- which had accounted for less than half of the industry volume in 2007 -- rose to 57 percent in May.

She said past trends have shown Americans will continue to drive despite high gas prices, but will drive more fuel-efficient vehicles and consume less fuel.

"History shows that we’re going to continue to see congested roads while gas tax revenues decline even further," she said.