The Transportation Department confirmed Fridaythat higher gasoline prices are curbing the number of miles logged on American roadways. The department’s Federal Highway Administration said monthly data shows that the estimated “vehicle miles traveled” (VMT) on all U.S. public roads for March 2008 dropped 4.3 percent compared with travel for the same month a year ago. This is the first drop in March travel figures since 1979. “At 11 billion miles less in March 2008 than in the previous March, this is the sharpest yearly drop for any month in FHWA history,” the administration said.

Americans are showing a modest willingness to cut back. Cumulative VMT has fallen by 17.3 billion miles since November 2006. Total VMT in the U.S. for 2006 topped 3 trillion miles.

The statement also notes that greenhouse gas emissions fell by an estimated 9 million metric tons for the first quarter of 2008. Though the statement doesn’t explicitly link the decrease in driver miles with fewer greenhouse gas emissions, the assumption is that there is a connection.