MILWAUKEE — With sweat dripping from your brow and a tightening grip on the steering wheel, it can feel like a decision better suited for the steely resolve of 007 or Ethan Hunt. Like deciding between a red or yellow wire as a countdown to zero ticks closer and closer to impending doom. But this decision isn’t dependent on picking the right colored wire. It’s choosing what to do at the right colored light.
Traffic lights.
A press of the right pedal or left pedal could spell disaster or delight. But it’s a decision that is influenced by engineers to ensure whatever choice you make, you’ll survive it.
“The timing of those signals are important to ensure that, first of all, we don’t have collisions,” Jay Beeber, Director of Policy & Research at the National Motorists Association (NMA) said. “Second of all, that the enforcement of that signal is fair and equitable, so you have to get the right signal timing for that.”
While traversing hundreds of different intersections across the area can feel the same, each one is reviewed by engineers to ensure the timing of the green light, yellow light and red light are precisely reviewed to keep everyone safe. From the people with their hands on the steering wheel, the handlebars of their motorcycle or bicycle or even the people with two soles on the ground.
But it’s not as simple as just choosing a time. The Federal Highway Association (FHA) recommends yellow lights range somewhere between three and six seconds long. Beeber says the NMA makes slightly more specific recommendations.
Generally speaking, the NMA suggests engineers give at least three seconds of yellow on roads with speeds of 25 mph. For every five miles per hour the roadway increases, the general recommendation is to add another half second to the length of the yellow light.
Beeber says the NMA suggests engineers conduct speed studies to understand the true speed of motorists on the roadway. If that’s not possible, he says the NMA suggests engineers add seven miles per hour to the posted speed limit and make decisions on the length of yellow light times based on those estimates.
“This becomes a very complicated thing for engineers and there is no perfect answer for this,” Jay Beeber. “But in general, you just want to make sure you’re not forcing people to slam on the brakes.”
Speed is one of the biggest factors in making this decision, but Beeber says there are an incredible number of variables. Weather conditions, distance to the light and each driver’s reaction time are just a few ways each light will vary from person to person.
“If we don't give them enough yellow light time, we create what’s called a dilemma zone,” Beeber said. “That’s a place in the roadway in which the driver neither has enough roadway to stop safe and comfortably nor enough yellow light time in order to get through the intersection before the light turns red.”
The I-Team went out to Dr. Martin Luther King Jr. Drive and Locust Street to ask drivers what they do when they see a light switch from green to yellow.
“Slow down and proceed with caution,” one man said.
“I stop,” a woman said.
“I slow down to stop because I have two kids,” another man said.
“25 percent of the time,” one man said. “I go through. I try to look around to see how the traffic looks. Occasionally, because you’re in a hurry.”
But that length of time can change from intersection to intersection on the same stretch of roadway. The I-Team compared two sections of North Avenue; at 35th Street in Milwaukee and 88th Street in Wauwatosa. According to speed limit signs, both sections are 30 mph and both intersections are roughly the same size. Despite being just over three miles apart, the intersections also have many differences; traffic frequency, pedestrian frequency and cross-traffic frequencies are vastly different.
In comparing the yellow light times by hand, North & 35th had times around 3.9 seconds and North & 88thStreet were around 3.4 seconds.
“Every intersection is different,” Elizabeth Lloyd-Weis, Traffic Systems Unit Supervisor at the Wisconsin Department of Transportation (DOT) said. “Speed limit, size of the intersection, traffic movements, traffic volumes and then the proximity of other traffic signals can impact the timing at each location. There are a lot of variables to take into consideration.”
WISDOT follows guidelines from the FHA to have yellow lights between three and six seconds. Lloyd-Weis says the Manual on Uniform Traffic Control Devices (MUTCD) helps guide the state and municipalities on how to time their own lights.
“Whether that is a county or a city, it’s up to each individual municipality to follow those Federal guidelines to determine the signal timing for their locations,” Lloyd-Weis said.
But whether a traffic light has a three-second yellow or a six-second yellow, the message is the same.
“If you can do so safely,” Lloyd-Weis said. “Stop.”
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