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 also would 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 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.
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.
Tarnoff and many other traffic engineers instead favor adaptive signal-timing systems first adopted 30 years ago in the U.K. 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.
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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.
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Food for thought
Here are some things about traffic congestion to think about while waiting for the light to change:
– 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 from 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.
– No traffic signal wait is forever. The longest standard cycle time is three minutes.