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Merge Like a Zipper for Better Traffic Flow through Work Zones

June 24, 2019
Have you ever left the parking lot of a huge sporting event or concert and noticed how drivers take turns getting into the exit lane? That technique is called the Zipper Merge, and it's the most efficient way to move many cars through a limited number of lanes.

The zipper merge is also designed to improve traffic flow through the heavy congestion caused by road construction. Instead of drivers merging early into one lane, which can cause one long line of traffic, the strategy is to use both lanes and wait to merge until they get near the lane closure. Like a zipper, drivers fill in both lanes and take turns merging at one point.

Due to the fact that St. Peters' residents are generally well-mannered and considerate, the idea of getting ahead in the open lane when a sign says, "Lane Closed Ahead," goes against our nature. St. Peters Transportation Engineer Amanda Rich said drivers in the open lane may see the drivers in the closed lane as cutting in line or being rude, which could lead to not letting a vehicle merge when they get to the lane closure.

While rushing to the front of the empty lane and cutting in may be considered impolite, according to recent studies cited on the Missouri Department of Transportation (MoDOT) website, traffic flow improves when both lanes are full and the cars take turns getting into the open lane near the lane closure.




CHECK OUT A MODOT VIDEO that helps explain the zipper merge.



By using both lanes up to the merge point, Rich said the queues/backups are much shorter and the difference in speed between the open lane and the closed lane is reduced. "A sense of equity and fairness is created because everyone is moving at the same speed," she said, "resulting in safer and smoother driving conditions for everyone within the work zone."

The zipper merge has been adopted as a Best Practice by the Federal Highway Administration (FHWA). Minnesota Department of Transportation is recognized as being a pioneer of studying, publicizing and implementing the zipper merge in work zones. According to the FHWA, with proper execution, the zipper merge can reduce traffic backups by up to 40 percent in areas with lane reductions.

The work zone on Mid Rivers Mall Drive at Cottleville Parkway was the first location where St. Peters encouraged drivers to utilize the zipper merge. Rich said it was a spot where they noticed long queues as a result of drivers merging very early in anticipation of the lane closure. The Streets Department used electronic message boards to encourage people to merge like a zipper through the Mid Rivers Mall Drive Corridor Improvements project area.

"I have received both good and bad feedback about the zipper merge there," Rich said. "As the word gets out and more people try it out, I think drivers will begin to understand the benefits of the zipper merge."



"As the word gets out and more people try it out, I think drivers will begin to understand the benefits of the zipper merge."



Rich added that many agencies started ad campaigns to spread the word about the zipper merge over the past few years, but the concept has been around much longer. "Folks all over the country are merging like a zipper," she said, "Including, but not limited to, Washington, Arizona, Minnesota, Oklahoma, Iowa, Indiana, and Maryland. Around the globe, drivers in Canada, Australia, and Germany also utilize the zipper merge."

"Anytime anyone asks me about it, I am happy to explain it and refer them to some videos online that demonstrate how the zipper merge works," she said. "There are also numerous websites that give information about the zipper merge."

Regardless of how you merge, Rich reminds residents that work zones can change from day to day, and even hour to hour, so always slow down and pay attention.