As most drivers know, not all intersections are created equal. Some are more dangerous and difficult to navigate than others, and a study from the University of Texas at Austin says the primary factor in determining an intersection’s safety may be the presence of flashing traffic signals.
The study, led by Cockrell School of Engineering professor Chandra Bhat, claims the presence of flashing lights — red or yellow — increases the probability of an accident by more than threefold.
“What we did was look at many factors that impact risk propensity, such as stop signs, solid traffic lights or even no traffic controls at all. What we found is that flashing lights came out to be the most crash risk prone by far,” says Bhat, who, along with two graduate students, used crash data collected by the Texas Department of Transportation.
This first-of-its-kind study was born out of Bhat’s desire to analyze whether the risk of one intersection has any bearing on crash risk at nearby intersections. What he found is that there is a spatial relationship between the two. In other words, if one intersection is more prone to crashes, nearby intersections also will be affected.
Intersection and intersection-related wrecks account for about four of every 10 crashes.
“The positive takeaway here is that if you make one intersection safer, that means you’ll also be making nearby intersections safer as well,” Bhat says. “We have been underestimating the benefits counter measures like this have in preventing accidents.”
As for the flashing-light intersections, Bhat says his study didn't focus on the reasons why they are more crash-prone than those with solid lights or stop signs. Anecdotally, he says, it may have something to do with driver confusion and misinformation.
“Perhaps drivers don’t exactly know what they are supposed to do at a flashing light. They see a flashing light and they think, ‘Am I supposed to stop? Slow down? Keep going?’ It could be pure confusion,” he says. “Our study suggests that if confusion is causing this, perhaps we need more information campaigns out there educating people about the proper way to navigate flashing intersections.”
Seeing the light
Yue Liu, assistant professor of civil engineering and mechanics at the University of Wisconsin-Milwaukee, has studied traffic intersections extensively and says he isn’t surprised by Bhat’s findings. He compares it with studies that have been conducted on countdown timers versus normal traffic signals.
Many studies have indicated that countdown timers — which alert pedestrians to how much time they have to cross an intersection — can make drivers envision the change of traffic signals and tend to encourage them to pass the intersection during the yellow time or even run the red light. Similarly, Liu says, drivers can visualize a blinking light farther in advance than they might see a stop sign.
“They can then envision or presume that traffic from the conflicting leg will stop or yield when they are passing through the intersection, so they usually pass the intersection without caution,” Liu says. “If they can't visualize the blinking light in advance, drivers tend to slow down to approach the intersection because they are not sure if there is a stop sign ahead.”
Rallying for roundabouts
Russ Rader, a spokesman for the Insurance Institute for Highway Safety, says the institute supports elimination of many traditional intersections in favor of roundabouts, which are free-flowing circular intersections built around central "islands." An institute study of 23 U.S. intersections reported that converting intersections from traffic signals or stop signs to roundabouts reduced injury crashes by 80 percent and all crashes by 40 percent.
According to the highway safety institute, installing roundabouts in place of traffic signals also can reduce the likelihood of rear-end crashes. Moreover, crash severity is lessened since most roundabout crashes involve merging vehicles traveling at low speeds and, unlike traditional intersections, there's no incentive for drivers to speed up as they approach green or yellow lights.
Bhat’s study "drives home the point that driving can be a challenging activity that requires drivers to be alert to changing, and sometimes ambiguous, conditions around them,” says Carroll Lachnit, features editor at automotive website Edmunds.com. “While traffic engineers work to make intersections safer, we can do our part by being fully engaged and defensive drivers.”
The effect on auto insurance
Mike Barry, a spokesman for the Insurance Information Institute, says Bhat’s study likely will have little effect on the auto insurance industry.
“I doubt strongly that there is enough data out there for insurers to make a broad interpretation as to whether or not flashing intersections are necessarily good or bad,” Barry says. “When it comes to individual policyholders, it’s more important to an insurer to look at broader geographical criteria when determining rates for a driver, such as whether or not he lives in an urban versus rural area.”