Much of the Washington area ranks among the nation's worst spots for traffic congestion, a new study has found.

GPS maker TomTom collected the data. The company used its systems to calculate drivers' speeds every few minutes over a two-year period, then stacked the data up against the posted speed limit on the specific road. A city's traffic was defined as congested if drivers could travel at 70 percent of the speed limit, or slower.

Montgomery County placed fourth on the list (behind Seattle, Los Angeles and Chicago), with 37 percent of its roadways congested. The District was in seventh place, with 30 percent of its roads crowded. Alexandria ranked ninth, with 28 percent of its roads congested. Fairfax County stood at 13th place with 26 percent.

A big reason for the backups, according to traffic experts: The Washington area is too popular for its own good.

"Because it's a great place to live it's not a great place to drive," said David Buck, spokesman for the Maryland State Highway Administration.

In Virginia, the congestion comes from an influx of workers, said Bob Chase of the Northern Virginia Transportation Alliance.

"When you add tens of thousands of jobs and you don't invest in the infrastructure needed to support those jobs ... the end result is some of nation's worst congestion," Chase said.

But when it comes to much-needed road projects, Virginia Department of Transportation spokeswoman Joan Morris said, Northern Virginia is hampered by a budget crunch.

"We focus instead on managing congestion," Morris said. That includes not only synchronizing, but adjusting the cycles on traffic signals to ease gridlock.

In Montgomery County, there are a slew of costly projects underway to relieve road congestion, from widening Route 124 ($50 million) to constructing the $2.5 billion InterCounty Connector that will connect Interstates 270 and 95.

In the District, transportation officials are trying to quell congestion by adding bike lanes and streetcars while encouraging commuters to ride Metro.