Traffic congestion continues to worsen in American cities of all sizes, creating a 78 billion U.S. dollars annual drain on the U.S. economy in the form of 4.2 billion lost hours and 2.9 billion gallons of wasted fuel, according to a new study released Thursday.

"There is no 'magic' technology or solution on the horizon because there is no single cause of congestion," noted study co-author Tim Lomax at Texas Transportation Institute.

Traffic congestion problem is growing worse in all 437 of the nation's urban areas, said the Urban Mobility Report, which is based on 2005 figures, the most recent year for which complete data was available.

The report notes that congestion causes the average peak period traveler to spend an extra 38 hours of travel time and consume an additional 26 gallons of fuel, amounting to a cost of 710 U.S. dollars per traveler.

The report also focuses on the problems presented by "irregular events" -- crashes, stalled vehicles, work zones, weather problems and special events -- that cause unreliable travel times and contribute significantly to the overall congestion problem.

The researchers identify multiple solutions to the congestion problem that, they say, must be used together to be effective. These include: Get as much service as possible from existing infrastructure; Add road and transit system capacity in critical corridors; Relieve chokepoints.

"Congestion is a far more complex problem than is apparent at first glance," Lomax said. "The better the data we use to define the problem, the more successful we will be in addressing its root causes."