How Are Traffic Lights Timed?

9November 2021

MINNEAPOLIS (WCCO) — It lasts mere seconds but can feel like minutes. Getting stuck at a red light, especially with no traffic around, is frustrating at times.

We wanted to learn: How are traffic lights timed? And can drivers influence a light to change? Good Question.

“There’s some weird stop lights, I don’t know why they’re still there, where it feels like you just sit there for five minutes at a time,” said driver Joey Dispirito.

“Some people say nudging forward helps but I’m not sure how effective that is,” added Noah Hiniker.

Will flashing your high beams at a red light get it to change to green?

“That is definitely an old myth,” Steve Mosing said with a smile. He’s a traffic operations engineer with the Minneapolis Public Works Department.

How are the traffic lights timed?

“We have about 815 signals in the city of Minneapolis and most all of the signals are timed on what we call a pre-timed system,” Mosing said.

A majority of the traffic lights in the city run on a 100 second cycle, which covers the time of green, to yellow, to red, and right up to when it’s green again.

The cycles also vary, lasting a little bit during longer morning and evening rush hours versus off hours. They’ll adjust again for major events like Twins and Vikings games.

What type of technology senses cars at traffic lights? First and foremost is an elevated signal system, which is a fancy way of saying a camera. “The camera detects differentiation within the pixels it’s recording to make a determination that it’s a vehicle. Once a vehicle is detected, signal times can be adjusted if needed,” said Mosing.

There’s also a sensor in the pavement, however it doesn’t recognize a vehicle’s weight as some drivers might believe.

“The sensor in the street has an electrical flux. And so when a vehicle drives over it, it breaks that flux and it sends a call to our controller that says there’s a vehicle there,” said Mosing.

“What else can influence the light timing?

“Pedestrians of course,” said Hinkier. That’s especially important in Minneapolis where foot and bike traffic are part of city life. The light rail system also influences certain intersections.

“We also have technology that accommodates bus rapid transit. These are the new buses that you see out on the streets to give them priority as they go through the intersection to make those commutes shorter for bus travelers,” said Mosing.

Those factors, along with making each intersection work in unison across the entire grid system in Minneapolis, makes it a tall task.

“It’s more of an art to try to set that at the right sweet spot so that we can manage the traffic flow at posted speeds or less,” said Mosing.

When Minneapolis changed speed limits to 25 mph on neighborhood streets in 2020, traffic light times were adjusted. There will another be a citywide timing evaluation in about 4-5 years.


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