Why some traffic lights work better than others

SALT LAKE CITY — For anyone who's ever been frustrated waiting at a red light when no other cars are coming — this article is for you.

Our KSL team has had its own frustration with lights that don't work or ones that have gotten stuck waiting for what feels like forever. So we decided to look into how traffic lights work and why some do better than others.

Pulling up to an intersection, the light turns red. At the right traffic light, you're on your way in a matter of seconds. But some make you wait for pedestrians that aren't really there, give the green to a car that pulled up after you, or just seem to take an eternity. Why is that?

"That's part of the job that I really love is figuring out what is actually going on and fixing a real problem," said Bryan Meenen, Salt Lake City Traffic Control Center supervisor.

Meenen is the man in charge of making traffic lights work in Salt Lake City. He told KSL there's a handful of reasons some lights don't work as well as you'd like. A lot of it has to do with the range of technology each one uses, how often they're updated, and how they're programmed.

Meenen said of the roughly 400 traffic signals in Salt Lake City, his office manages at least 255 of them. Of those, 54 aren't programmed with any way to detect cars, 19 have loop sensors built under the ground to detect when cars pull up to the light, 63 use different fixed cameras to see cars approaching, and 117 use radar — similar to the radar guns police officers might use for traffic stops.

"The radar sends out a beam, and whatever's bounced back, we analyze it, and we can tell where the vehicles are at as they approach," Meenen said.

What they're not using yet is lidar detection, which stands for "light detection and ranging." It looks similar to an infrared image of cars and pedestrians moving and crossing through an intersection. Lasers create multiple points that detect both people and cars, giving traffic engineers an expanded view of the intersection and the ability to adapt to traffic issues in real time.

"It's basically like an AI picture of what's happening in a particular intersection. It can give us information that in the past we have not really been able to get," said UDOT spokesperson Mitch Shaw.

The Utah Department of Transportation is using it right now at state-managed intersections like Washington Boulevard and 24th Street in Ogden. It's one of 56 lidar traffic signals in Utah, with 77 more rolling out statewide at the end of the month. UDOT's goal is to upgrade 10% of the state-managed intersections each year, until all 1,425 are outfitted with lidar.

"It's really the wave of the future. It's what the traffic signals are going to look like," Shaw said.

Places like Salt Lake City plan to begin adding lidar to intersections next summer, but at the city level, swapping out the technology is slow and expensive. City traffic engineers told KSL upgrading an intersection including lights, poles and all costs the city $560,000 a pop, and Salt Lake only has the money and manpower to do three to five a year. That leaves many city-managed intersections aging out with old technology.

"We're getting about 40 years out of a signal. We have much older signals right now, but we're shooting for 40 years," said Meenen.

Salt Lake City's oldest traffic signal at 2700 S. Highland Drive hasn't been updated with new tech in 90 years.

Other factors include how lights are programmed. Depending on the intersection location, it may be programmed to sync up with other traffic lights, giving some drivers good odds for greens, or red after red if you don't go with the flow.

Where there's high foot traffic, lights could automatically start the timer for pedestrians, physically there or not, or only activate when you push the button.

And then there are traffic lights like the one at Cougar Boulevard and Campus Drive at BYU. It doesn't matter who drives up, when or where; it always gives you the right light, real fast.

"It's very, very responsive. It's a great way to run an intersection. Actually, it's the best way to run an intersection," said Mike Wright, with Pinetop Engineering.

Wright manages the radar-based light for the university. He said half of its success is that it's not tied to a larger traffic grid.

"One of the unique things about this intersection is that it's isolated, which means it's able to be responsive to everything that's happening on each approach," Wright said.

So, if you could handpick one, Wright feels everyone would love this at every intersection, but there's no practical way to program the thousands of Utah traffic lights like this.

"The math becomes impossible, in essence," Wright said.

One of the most interesting factors KSL discovered, looking into traffic lights, is that they don't necessarily account for who pulled up first. Each traffic computer goes through its cycles and phases based on safety.

"Safety is the No. 1 priority. Efficiency is No. 2," Meenen said.

So the system isn't perfect, but it is built on safety.

"It's not a fair system; it is a safe and somewhat efficient system," he said. "I've not found a perfect detection yet. However, we're getting better all the time."

So there could be any number of reasons why one traffic light is better than another: what tech it uses, how old it is or how it's programmed.

Whatever you run into, as long as it's not flashing, the light is going to turn green.

If you have a light that's always frustrating you, or doesn't appear to be working well, both Salt Lake City and UDOT have a way you can report it. Those can be found at the Salt Lake City traffic website and the UDOT reporting website.

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