Stop and Go Lighting

Green…yellow…or red….There’s a science behind stoplight timing.

The city of Naperville has 155 traffic signals…and 91 of them are maintained by the city.

So how do they determine how long you wait at any intersection?

Project manager Andy Hynes is the bright bulb behind many of the city’s traffic lights. He says to determine their timing, traffic engineers first collect data at each intersection such as vehicle counts, visibility, number of lanes, speed limit, among many other factors.

“We take all those [factors] [and] put ‘me into some simulation software that software is designed to come up with a set of optimized timings,” said Hynes. “We take the results of that modeling [and] we input that out into the field, into the actual traffic signal controllers at each intersection and then what’s tat done we do some field observation and basically tweak the original parameters that were given & try to make the system as efficiently as possible.”

Traffic signals are synchronized to a set cycle, taking 80 to 160 seconds for a full rotation from green to yellow to red to green again. Cycles typically change throughout the day to reflect traffic patterns at the time.

“During the day time, the signal’s going give the majority of the green time to the main street and that’s why often times when you’re on a side street, you have to wait a little bit longer,” Hynes explained.

But some items can throw off a light’s cycle like construction near the signals, emergency vehicles proceeding through an intersection, pedestrian push buttons, and most commonly, traffic. Devices like a video camera can detect when vehicles are present, some triggering a change in a traffic light to give the green light to the busier street. The most common and reliable devices are inductive loops routed underground.

“There’s usually about 3 6 by 6 loops in the pavement, in each lane and once a vehicle drives over one of those loops, the conductivity of the vehicle creates a disturbance in the electrical field there and that is then relayed into a controller,” Hynes explained.

Every year, the city typically spends more than $2,000 in ongoing electricity for the lights and in repairs, plus $250,000 for each new traffic signal that needs to be installed.

If you have an intersection you think the city needs to look at, you can email them at traffic signals at


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