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SALT LAKE CITY — Ask Utah drivers about coordination of traffic lights and you'll get an earful. It's been a big issue for a lot of cities all over the state: idling cars waste time and create more air pollution.
Utah is one of only two states in the country that can track real-time traffic signal performance — so traffic operators know the speed drivers should travel if they want to see more green on their commute.
“The closest thing we have to a magic speed is the speed limit,” said Mark Taylor, traffic signal operations engineer for the Utah Department of Transportation.
To test the "magic," KSL's Jed Boal recruited producer Candice Madsen.
“I’m usually thinking the faster I go, I’m going to hit more lights,” Madsen said.
Boal used a different philosophy: “I think that if I go the speed limit, I’m going to hit more lights.”
The two drove the Bangerter Highway, University Parkway, State Street and Foothill Drive corridors in Salt Lake and Utah counties. They ended up hitting the same number of green lights once Madsen realized that if she stuck to the speed limit she had a better chance of catching the green wave.
“Speed is self-regulated in coordinated signal systems. Drivers traveling too fast will arrive on a red drivers traveling too slowly will not arrive at the next signal in time to use the green indication,” Taylor explained.
Traffic signal coordination cannot eliminate all red lights, he said, but it is effective in reducing stops and delays.
Last year, UDOT re-timed the signals along Bangerter Highway and increased the percentage of vehicles arriving on green by 19 percent during the afternoon commute.
During the month of October, UDOT reported 70 percent of drivers arriving on green lights statewide.
Speed is self-regulated in coordinated signal systems. Drivers traveling too fast will arrive on a red drivers traveling too slowly will not arrive at the next signal in time to use the green indication.
–Mark Taylor, UDOT
Taylor said traffic engineers are constantly amused by all the tricks drivers use to try and trigger the lights.
“It is entertaining these days watching motorcyclist, for example, thinking that we still have pressure plates out there in the field,” Taylor said.
Weight-detecting pressure plates have actually been extinct in Utah for over 40 years. Some people also wonder if flashing headlights will trigger the light, but Taylor said that is also a myth.
Most traffic lights in Utah use a magnetic loop system that detects when a vehicle is waiting at the light, but those are also being replaced by Wavetronix radar devices which do a better job at detecting all users who need to trigger the light.
“The all-carbon bicycles these days just do not have enough metal on them to trigger the inductive loops,” Taylor said.
There are approximately 1,900 traffic signals in Utah; 60 percent are operated by UDOT and 40 percent are operated by cities and counties.
Taylor said drivers should expect no more than a 90-second stop for a red light. “If drivers are waiting for longer than that, the detection has probably malfunctioned,” he said.
Drivers are encouraged to report such situations on UDOT’s website or by calling 1-801-887-3700.
