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SALT LAKE CITY — You're approaching an intersection and the traffic light turns yellow. Do you hit the brakes to stop or hit the gas and try to rush through the intersection?
Most motorists get through intersections safely every day. But just one bad decision can put many people's safety at risk. It's a dilemma that traffic engineers have spent countless hours trying to solve.
All drivers know green means go, red means stop and yellow means "can I make it?" Many times, the answer isn't obvious.
"I'm sure every driver has experienced that dilemma zone. You're not quite sure what to do," said Richard Porter, assistant professor at the University of Utah's Department of Civil and Environmental Engineering.
The dilemma zone is what traffic engineers call a section of road that emerges at an intersection when the light turns yellow.
Here's the dilemma: Drivers don't know if they should slam on the brakes or hit the gas in hopes of clearing the intersection. The first choice could cause a rear-end crash. The second could result in a T-bone collision.
"From the time you're age 4 to, I think 35, the number one cause of death is traffic. I think people just don't realize that," said Porter.
He helps lead the University of Utah's traffic lab. He said the goal of every traffic engineer is to find a yellow light's sweet spot, so there's no dilemma zone. If the light changes from yellow to red too soon, there's a higher risk of crash. But if takes too long, drivers might be more willing to risk it and try to beat the light.
"Over time, drivers are going to start to understand there's more and more yellow time, so you're likely going to have more and more people use it," he said.
Yellow lights in Utah last from three to six seconds, according to Mark Taylor, a UDOT traffic signal engineer. He said the timing isn't pulled out of thin air. It's based on several factors including the speed and slope of a road. An additional second is added for driver reaction time The total time usually ends up being about one-tenth of the speed limit.
"If the speed limit is 50 miles an hour, we use a five second yellow," he explained.
UDOT uses radar technology to shrink the dilemma zone. Radar detectors are perched above many intersections in the state. When they pick up on an approaching car, they will add a few seconds of green time onto the light if the vehicle is within the dilemma zone, Taylor said.
For example, a car approaching a traffic light from about 300 feet away, going about 45 miles an hour is in the dilemma zone. Radar tacked three more seconds onto the green light.
"That's why we are using this radar, to help drivers get out of that dilemma zone," Taylor said.
Chuck Clegg, and instructor at A-1 Driving School said, "We really can't depend on all the electrical things to be working correctly, and we can't depend on the painted lines to be painted exactly correctly. We have to be the deciders."
Clegg has been teaching teens and others how to drive for more than 35 years. Clegg said the key to making a good decision at the yellow light is being alert to what's in front of and in back of your vehicle.
"If you look in your rear view mirror and there's a car coming up behind you that's going faster than you are, certainly you wouldn't want to make a quick stop in front of them," he said. "So we instruct the kids to go through."
Still, each of the people we spoke with said if you can stop safely at a yellow, do it.
