A bright idea for easing traffic

A major problem: speeders. Park found that his model would not conserve fuel well without some basic traffic enforcement to mute extreme driver behavior. For instance, drivers that accelerate to 55 miles per hour in a 45-m.p.h. zone create too wide a “distribution of desired speed” for effective fuel savings. “If you can assume a higher enforcement rate, or a better compliance rate, it may be possible to achieve both the fewest delays and the best fuel consumption,” Park says.

If traffic-timing systems were updated using conventional methods, the US could cut fuel consumption by up to 10 percent – about 17 billion gallons a year, the National Transportation Operations Coalition found in its 2007 traffic-signal report card. (Emissions also would be by cut more by than 20 percent.) If Park’s hyper-efficient micro-model traffic-timing method were widely applied, another 1 billion to 2.5 billion gallons could be saved.

“With the increase in computer horsepower and improvements in sensors [embedded at intersections], we could take a lot of ideas and put them into the much more doable range for city staff and budgets,” says Timothy Lomax, a research engineer at Texas A&M University’s Texas Transportation Institute and lead author of its national mobility report.

Last year’s mobility report found congestion across 437 urban areas wasting 2.9 billion gallons of fuel. Signal timing isn’t the only cause of congestion, but it’s one of the “top five” reasons, he says, and may account for as much as half of the congestion.

For about $250 million a year – about $1,000 per intersection – the entire US could have well-timed lights, far less congestion, and far higher fuel savings, says Philip Tarnoff, director of the Center for Advanced Transportation Technology at the University of Maryland.

The payoff in fuel savings alone, calculated before this year’s run-up in gas prices, was a return on investment of at least 40 to 1 and perhaps more.

But politicians tend instead to spend billions on building or widening roads – a far more costly approach to yield similar results, Dr. Tarnoff says. “You would think traffic-signal optimization would be a no-brainer,” he says. “But it’s hard to get the federal government to fund traffic light timing. It’s kind of dull stuff that’s just not going to get votes.”

Some cities, however, have taken the initiative and are reaping rewards. After Plano, Texas, received a “C” on its 2005 traffic-signal report card, the city got to work timing its lights and won a “B” grade last year. It also saved about 850,000 gallons of gas, eliminated 36 million unnecessary stops, and cut 745,000 hours of delays, it estimates.

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