Drivers are spending less time stuck in rush-hour traffic for a second straight year, the first-ever two-year decline in congestion as high gas prices and the economic downturn force many Americans to change how they commute.

In individual cities, Los Angeles traffic is getting better but is still the worst in the nation. Washington’s is getting worse, now ranking second.

The average U.S. driver languished in rush-hour traffic for 36.1 hours in 2007, down from 36.6 hours in 2006 and a peak of 37.4 hours in 2005, according to a study being released Wednesday by the Texas Transportation Institute. Total wasted fuel also edged lower for the first time, from 2.85 billion gallons in 2006 to 2.81 billion, or roughly three weeks’ worth of gas per traveler.

The records go back a quarter-century, to 1982. The last time traffic congestion had declined was in 1991 amid a spike in oil prices during the first Gulf War.

This time, demographers attributed the decrease to a historic cutback in driving as commuters reduced solo trips, took public transit or carpooled after gas prices surged toward $4 a gallon and then the economy faltered. The housing downturn beginning in 2006 also reduced U.S. migration to far-flung residential exurbs.

But it won’t last. “Congestion won’t be as bad as before for a while, but it will still be very frustrating, very unreliable and it will take a lot of time out of your day,” said Tim Lomax at the Texas Transportation Institute, which is part of Texas A&M University. “The average traveler still needs 25% more time for their rush-hour trips.”

The Los Angeles metropolitan area, with its car-pool lanes and emerging mass transit, shed two hours of wait-time in rush-hour traffic. Still, its sprawling freeway system remained the nation’s worst for congestion.

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