WASHINGTON -- Fine-tuning controls on the nation's traffic signals would cut U.S. road congestion by as much as 10 percent, transportation experts estimate.

It would also reduce air pollution from vehicles by as much as a fifth, cut accidents at intersections and save about five tanks of gas annually per household, according to the National Transportation Operations Coalition, an alliance of federal, state and local traffic departments and equipment-makers.

That's the good news. The bad news is that the average local traffic department earned an overall grade of D on the alliance's latest report card. Streamlining intersections is happening in only some cities and states, even though it's eminently doable.

"People who say we can't do anything about congestion are wrong. We can do lots," said Joel Marcuson, a specialist in urban intersections who's with the Jacobs Engineering Group Inc. in Phoenix.

Right now, however, three out of four of the nation's 300,000 traffic signals need replacement or timing adjustments for optimum performance, according to the U.S. Department of Transportation.

Technologically, most U.S. traffic signals remain very 20th century, said Philip Tarnoff, director of the Center for Advanced Transportation Technology at the University of Maryland in College Park.

Roadside or centralized timers drive most of them by changing lights at scripted intervals, he explained. "They tell the signals: 'It's 6 a.m. Use timing schedule A until 9 a.m. Then use timing schedule B until 4 p.m.'"

Tarnoff and many other traffic engineers favor adaptive signal-timing systems first adopted 30 years ago in the United Kingdom and Australia. They measure traffic minute-to-minute with cameras or in-pavement sensors and automatically adjust signal times to maximize flow for existing conditions, including accidents, construction and bad weather.

These adaptive signals haven't caught on with local U.S. traffic departments, however. They're costly and challenging to program, and initial local U.S. experiments with foreign-made systems failed. So did efforts to come up with home-grown ones.

Samuel Staley, director of urban and land use policy at the Reason Foundation and a specialist in transportation, said traffic departments often lack the money, skill and local political power to innovate with adaptive technology.

Whatever the reason, more than 95 percent of U.S. traffic signals today are still timer-driven, Tarnoff estimates.

Your town might need improvement, traffic engineers say, if your answer is "no" to any of these questions:

• Can you sometimes make it through six to eight consecutive intersections on green lights?
•  Is there useful traffic information on the radio and on roadside message signs?
• Is it rare that there's no cross traffic when you're stopped at a light?
•  Can you drive into the next jurisdiction without encountering congestion at the line?
•  Are predictable traffic jams, such as the post-game exits from stadium parking lots, handled adroitly?