The U’s Utah Traffic Lab is working in partnership with Utah Department of Transportation to develop methods for traffic light safety.
Yellow lights are sometimes confusing situations which call for fast decision-making, which traffic safety specialists call the “dilemma zone.”
One of the methods of making yellow lights safer in the dilemma zone is adding radar sensors that will extend the time of green lights by a few seconds.
“When that light changes from green to yellow that driver has to make a decision, ‘Do I go or do I stop?’ So we use this radar that helps to add a few seconds of green time onto the light when cars are in that decision making zone,” said Mark Taylor, a UDOT traffic signal engineer.
Utah has been implementing this technology on many of its high traffic roads since 2006.
The dilemma zone offers several safety problems and it is important for the yellow light’s timing to be precise, said Xiaoyue Cathy Liu, a professor working in the U’s traffic lab.
“If the yellow light is too short then people might run into a dilemma zone, so people do not know if they should go through or stop,” Liu said. “So if they stop it may result in a rear end clash with the following vehicle or if they just go it may result in a crash with the opposing traffic stream.”
The United States Department of Transportation reported in 2010 that 36 percent of car accidents occur at intersections. Nearly a quarter of these occur while taking a left turn.
“The most severe accidents are actually the right-angle crash. This is when you have a crash with a vehicle coming in the opposing traffic stream,” Liu said.
This is known as a T-bone crash, and is much more dangerous than rear end collusions, Liu said.
The Federal Highway Administration stated that there were 2.3 million reported crashes occurring at intersections during 2008, resulting in 7,700 fatalities and roughly 733,000 injuries.
Utah’s yellow lights work on timers that are related to the posted speed limit on the road. Taylor said in general the yellow light timing is one-tenth of the recommended speed.
“If the posted speed is a 40 mph, we use a four-second yellow, if the posted speed is 45 mph we us a four and a half yellow. So it is approximately a tenth of the posted speed limit,” Taylor said.
Kimy Workman, a freshman in film and media arts, said that she has almost been in accidents a number of times at stoplights.
“I’ve almost been hit plenty of times. It’s scary when you’re a pedestrian and walking,” Workman said.
Workman said, however, that she is one of the responsible drivers, and has never run a red light.
Ben Silcox, a junior in chemical engineering, said he has never been in an accident at a yellow light, but he does not believe the yellow light system is working.
“Everyone here, at least in Utah considers them just part of the green light because you only have to be past the first line in the intersection to count as legally not running the red light,” Silcox said.
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