- The Washington Times - Monday, June 4, 2001

One second of a yellow light can make the difference between a traffic jam and a smooth flow. Timing is everything to those figuring out traffic-light patterns for a busy city. Leave one light on for a second longer than the one down the block, and traffic in the city can slow to a crawl in an instant.
How difficult is it to strike this delicate balance?
Just ask William McGuirk, chief of the District of Columbias traffic-signal system, and he will pull out half-inch-thick binders full of maps, charts and measurements.
Each of the citys estimated 1,500 traffic signals — which cost between $125,000 and $150,000 apiece to install — is born out of the brown-colored binder, he says. Each binder contains pages full of algebraic formulas and carefully drawn maps of the intersection a particular signal will control. It includes time sheets, which outline to the millisecond when a light should turn red, yellow or green.
Each signal is represented by a tiny bulb on a banner-type electronic grid showing an aerial view of the District, its streets and all of its traffic lights. The bulbs alternate between red and green with the signals they represent on the street.
Mr. McGuirks team of 30 traffic engineers monitors the grid 24 hours a day, seven days a week.
"Every signal is uniquely timed," Mr. McGuirk said in his office in the Reeves Municipal Center in Northwest, site of the citys traffic center.
"Its a monstrous task, and you have to be very careful," he added. "Changing something by a couple of seconds can make a huge difference in our world. Change a number and it can create a ripple effect down the street."
To time a signal, Mr. McGuirk first measures an intersection, then tries to determine the walking speed of pedestrians crossing the intersections. "You measure the length of a crosswalk, then divide that number by 4 feet per second and you get the average walking speed," he said.
Mr. McGuirk adds to the mix the estimated 1.3 seconds it takes a driver to react to the color of a light.
With that mathematical foundation, he figures out three separate timing plans for each signal: one for regular traffic, one for morning rush hour and another for evening rush hour. The plans could differ by as much as 10 seconds.
Most of the lights operate on 80-second cycles. But depending on traffic conditions, some lights operate on 90-, 100- or 110-second cycles. "Our goal is to make all [the traffic lights] work together as harmoniously as possible," Mr. McGuirk said.
When a new signal is introduced to the system, Mr. McGuirk must reconfigure the timing cycles of all the traffic lights in the District.
The way Mr. McGuirk sees it, commuters never will be able to travel into downtown Washington without getting stuck in some kind of traffic jam. Thats partly because Virginia and Maryland have their own timing cycles and motorists have to enter a different traffic pattern once they reach the District.
"It can get pretty rough," Mr. McGuirk said. "The District is basically taking freeway traffic, and motorists have to make a transition between the different traffic patterns. Youre used to driving 50 to 55 miles per hour and then all of a sudden youve got to come to the reality of the situation."
Synchronizing lights among the two states and the District would be a good idea if the traffic signals were spaced closely together on roads that cross over from Maryland or Virginia into the District, he said.
Commuters traveling Wisconsin Avenue in Northwest could see a difference soon. The traffic signals along the heavily traveled Route 355 corridor will be synchronized to alleviate traffic congestion throughout the day.
"We want to help commuters in any way we can," Mr. McGuirk said.


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