All in the timing

The traffic light at Mount Auburn and Bloomfield roads is fixed. But for two weeks, its off-kilter green-yellow-red cycle puzzled Geoff Dial.

The special projects coordinator for the city of Cape Girardeau is responsible for the city of Cape Girardeau's 19 traffic signals. On Monday, Dial was at the intersection of Siemers and Lambert drives to change a burned-out amber bulb. Last week he figured out the reason a light at Broadway stayed red and gave drivers on the side street Caruthers Avenue a constant green.

"Someone broke the pedestrian button, and Caruthers was getting a constant call [for green]," Dial said.

He traced the Mount Auburn-Bloomfield problem to a faulty coaxial connection.

"It wasn't bad all the way, just when wind would blow," he said. "Every time I went out there it worked fine."

Public Works Department Special Projects Coordinator Geoffrey Dial explained how traffic signals work at the corner of Siemers and Lambert Monday, November 26, 2007, in Cape Girardeau. An entire intersection with sensors, one type of sensor is the camera at the top of the frame that monitors when cars enter the shot and adjust signals accordingly, costs roughly $250,000. (Kit Doyle)

Far and away, the most challenging part of traffic light management is adjusting traffic lights' timing cycles, he said.

Drivers invariably experience signal problems first, said Craig Compas, the MoDOT engineer who oversees the state's 127 traffic lights in Southeast Missouri's 14 counties. The state manages 24 lights in the city of Cape Girardeau, along Kingshighway and on Route K.

Just getting the proper timing of the lights takes "a mix of art and science," Compas said. The state checks its lights annually unless they malfunction, he said.

Over the next few days, Dial and his boss, public works director Tim Gramling, will tweak the city's lights at intersections destined for heavier holiday traffic, allowing for longer green lights on busier roads.

Each intersection presents a different challenge to the technology used by the lights to detect traffic.

Jason Rodriguez lowered himself after replacing a yellow light in the traffic signal at the corner of Siemers and Lambert Monday, November 26, 2007. (Kit Doyle)

Most lights detect traffic one of two ways. A figure-eight-shaped electromagnetic device in the pavement is designed to sense cars and send signals to the light above the intersection. Newer technology at other crossroads uses a video device that compares a present image with a recording of the empty intersection and alerts the light to switch as cars approach. The lights are intended to allow a smooth flow of traffic for drivers, and minimize stops.

Mechanical failures happen, Dial said, but safety measures are built in.

A four-way green signal trips an alert that instantly switches the lights to four flashing red lights.

Getting impatient at a red light can cost a driver, said Sgt. Kevin Orr, of the city of Cape Girardeau's police department. He said the most common reason drivers blow through stop lights is haste, though distraction is a close second. A ticket costs $125 and adds points to a driver's record, he said.

Police officers keep an eye on signal cycles and report problems, Orr said. They can also be dispatched to verify signal complaints.

"If we get a complaint that lights are not cycling properly, we do go out and check that," he said. Sometimes, though, the problem is driver error.

"Cars don't pull all the way up to the lines to trip the sensor," he said.

Engineer John Swarney designs traffic lights for the Davenport, Iowa-based Brown Traffic Products Inc., which supplies equipment to the city of Cape Girardeau. He said electronic controllers provide eight options for traffic patterns, including left turns from each intersection's four sides and four for pedestrians and bicyclists.

"As a motorist, you want to roll though town without stopping," he said. "So controllers are connected to a master controller and this allows what we call progression."

Swarney said the many variables make it tough to get the timing perfect.

"You have a 35 mph posted speed limit and are people going 38, 40, 30 miles an hour," he said.

Mix that with varying numbers of cars traveling at differing distances along a street toward an intersection and getting the timing right requires mathematical formulas and computer programming skills.

Embedded electromagnetic devices can't always sense motorcycles, bicyclists or pedestrians, Compas said. MoDOT-operated signals communicate via fiber optics and telephone lines linking them to a master control, meant to coordinate the timing of lights from one intersection to the next. City and state lights are not coordinated with one another.

Next week, Dial heads to Brown Traffic's Davenport headquarters for a series of classes in using Internet technology to manage traffic lights, and the elaborate technology that operates them.

To report problems with MoDOT lights, call 888-275-6636.

For city of Cape Girardeau lights, call 334-9151.

pmcnichol@semissourian.com

335-6611, extension 127

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Traffic lights, by the numbers

The Missouri Department of Transportation is responsible for 127 traffic signals in its 14-county southeastern district including 24 in the city of Cape Girardeau; 12 in Jackson, with a new one scheduled for installation before the end of 2009 at the intersection of Highways 34 and 72; 18 in Sikeston; and three in Scott City. The city of Cape Girardeau maintains 19 additional permanent traffic signals.

Red light violations, by the numbers

So far this year, 154 tickets were issued to drivers in the city of Cape Girardeau for running red lights; 29 to those who failed to obey flashing red lights; and 15 tickets went to motorists who violated such traffic controls as barricades or temporary stop signs. Last year, 190 drivers received red light violations.

In 1987, Cape Girardeau police issued 932 tickets for stop light violations.