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.

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Right now, 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.

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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 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.

Among the obstacles are a nationwide shortage of skilled traffic engineers, unfocused local political leaders with tight budgets and stodgy local traffic departments. For that matter, federal aid that could ease congestion goes mainly to building and maintaining roads.

Nonetheless, lots of cities and at least seven states — California, Florida, Washington, Minnesota, Maryland, Georgia and Texas — are finding ways to move traffic through intersections faster, according to the transportation engineers group.

Georgia focuses much of its energy on the 20-county area around Atlanta when it comes to traffic signal improvements. Since 2005, it has cut travel time in Atlanta's traffic corridors by 18 percent and time stopped by 39 percent, said Yancy Bachmann, assistant state traffic engineer. Macon and Columbus have also seen traffic signal improvements, he said.

And where does your metropolitan area stand?

It could 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 border?

—Are predictable traffic jams, such as the post-game exits from stadium parking lots, handled adroitly?

Most traffic departments can do better at each of three levels of traffic management, Marcuson and other experts said: individual signals, coordinated signals and regional traffic management.

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.'"

If timers are accurate, and the prescribed signal intervals are based on accurate and recent traffic surveys, these systems can do as well as fancier ones in typical traffic situations.

That's a big if, however. Most timed systems aren't refreshed and adjusted at the three-year intervals recommended for busy intersections or ones that see big changes in traffic due to new homes or businesses. In the industry self-report card issued last year, traffic departments nationwide earned a collective F for traffic monitoring and data collection, which are key to well-timed intersections.

"As a result, signals may not operate based on actual traffic conditions, resulting in delays," the National Transportation Operations Coalition's report concluded. The 417 departments in 47 states on whose data the grade was based control nearly half of all U.S. intersections.

Even perfectly tuned timer-dependent signal systems can't adapt to unpredictable roadway events such as accidents, construction and bad weather. Together, those factors cause half of U.S. traffic congestion, according to Transportation Department statistics.

For all these reasons, 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.

"They're resistant to change, particularly if it involves learning a new technology," Staley said. "The small cities don't have the depth of technical knowledge, and the big cities, while they have depth of knowledge, also have a lot more politics that resists innovation."

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

SOME OTHER STATES' TRAFFIC SOLUTIONS

— Texas, a U.S. leader in traffic signal efficiency since the mid-1990s, adjusts its state-operated signals every two or three years to reflect changes in traffic volume. Once in three years is a national goal unmet in many states. Austin, the capital, earned a rare grade of A on its National Traffic Signal Report Card for providing proactive annual maintenance to all the city's lights at no added cost to taxpayers.

— Washington state coordinates the timing of half the 1,000 traffic signals that the state is responsible for. It checks the timing of signals on busy arteries every two-and-a-half years. That compares with a three-year standard unmet in many states. In addition, the transportation department now reports directly to the governor rather than to a transportation commission.

— Minnesota, which is among the nation's leaders in traffic control, retimes signals on the state's main arteries every two years, said Steve Misgen, a Twin Cities metro traffic engineer. Most states and communities struggle to adjust their traffic signals every three years. Most signals can be adjusted from a central control center in Roseville, he added. The state's ratio of benefits to costs is well above 60 to 1, Misgen said, counting only gas savings from less waiting time at intersections.

— Maryland is a leader in coordinating traffic corridors; about half of the 2,700 signals that the state controls are linked to other signals to optimize traffic flow, said Eric Tabacek, the division chief of the state office of traffic and safety. Maryland adjusts signal timing every three years — and has done so since the mid-1990s. It's a standard that many states are struggling to meet. In addition, Maryland is experimenting with intersection video monitors that continuously adjust traffic light timing to maximize traffic flow.

— Florida, which is among the nation's leaders in traffic control, gets credit for its success in linking city, county and municipal systems to improve traffic flow, most recently in the Sarasota-Bradenton area and around Tallahassee. It's also a leader in managing lights from regional command centers. Mark Wilson, deputy state traffic operations engineer, said that checking the timing of Florida's signals every three years or less is a key goal.

— California has new money for traffic signal improvements, unlike most states. A 2006 bond issue yielded $150 million for the Los Angeles area. Top priority there and elsewhere goes to intersection improvements that improve driving time, cut accidents and reduce air pollution. Those that involve multiple jurisdictions working together also are favored under the traffic signal initiative whose first grants are expected later this month.

THINGS TO PONDER ON TRAFFIC LIGHTS

— Pedestrians could get more crossing time. "Walk" signals and other pedestrian controls currently assume that people cross streets at a pace of 3.5 feet per second. That would drop to 3 feet under a pending Federal Highway Administration proposal, according to Doug Hecox, an agency spokesman. "Pedestrians are getting older and heavier," he explained. At busy urban intersections, pedestrians would gain 2 to 4 seconds at drivers' expense.

— Commuting really is hell. Working women in a 2006 Texas survey rated driving to work their least favorite activity. Work itself came in second. Then came the commute home.

— If arterial congestion is chronic, blame left turns. "Traffic turning left is the inevitable primary problem," said David Hartgen, emeritus professor of transportation studies at the University of North Carolina-Charlotte. Often, it's a turning lane overflowing due to rush-hour demand and backing up through-traffic. Or a left-turn signal too brief to clear the turning lane. Or too much on-coming traffic.

— No traffic signal wait is forever. The longest standard cycle time is three minutes.

— Zen helps. When green lights are properly synched to a designated speed, going faster only gets a driver to a red light faster, explained Douglas Noble, director of operations and management at the Institute for Transportation Engineers in Washington, D.C. In other words, he continued, sounding a bit like Yogi Berra: "If you're not rushing to get somewhere, you'll get there just as fast."