Zipping through work zone delays

Posted in: Bridges, Construction, Highways


Is the “zipper merge” technique a better, quicker way for traffic to merge? As Departments of Transportation around the country continue to launch public awareness programs to teach drivers that merging farther down the road saves time, motorists are still divided on the practice.

A zipper merge occurs when drivers use all open lanes until they reach the lane closure. At this merge area, motorists from each lane take turns merging into the remaining open lane of traffic, mimicking a zipper being zipped. Confused? Check out this brief video to see the zipper merge in action.

This method runs contrary to routine driving practices – motorists tend to practice early merges, turning into the open lane as soon as they see a lane closure approaching. Yet according to multiple studies, zipper merging is a faster, safer way to merge two congested lanes of traffic into one. The Colorado DOT found that zipper merging in construction zones led to a 15 percent increase in traffic flow in addition to a 50 percent reduction in congestion. A zipper merge site in Michigan saw a six-mile congestion line reduced to three miles, saving drivers approximately 15 to 25 minutes. It has also shown promise in reducing the number of collisions. This partly attributed to the traffic in both lanes moving at the same speed, eliminating the speed differential created by one lane progressing faster than the other.

Because driving practices are deeply ingrained, DOTs across the country face similar difficulties while implementing the zipper merge into daily life. Public awareness can be successful, though. The Minnesota DOT and Colorado DOT have both successfully launched decade-long public awareness campaigns to teach drivers better merging practices. MnDOT’s campaign emphasizes the benefits of zipper merging by equating it with “creating a sense of fairness and equality” and not to be concerned with being “Minnesota nice”.

CDOT posts videos and signs process telling drivers to follow these easy steps:

  • Just wait
  • Use both lanes
  • Take turns
  • Merge late
Photo from NC Vision Zero

The North Carolina DOT went with more subtle approach, posting zipper merge road signs around Durham to gently remind drivers to merge farther down the road. Other states have also launched TV ad campaigns with video animations to educate current and future drivers.

With constant roadway construction and maintenance on roads, everyone is bound to encounter construction on a regular basis. Do you practice zipper merging on your daily commute?


Christopher Rossmiller, PE

About the Author

Chris Rossmiller, PE specializes in complex geometric design and traffic control. His designs work in conjunction with staging and maintenance of traffic plans to safely convey traffic information during a project’s construction phase.

Read more posts by Christopher Rossmiller, PE

2 responses on “Zipping through work zone delays

  1. I saw you are trying to promote the zipper merge. There is a way to get it to work. Instead of merging one lane into another, merge two lanes equally to the middle, then have the single file Lane be guided to the new Lane via cones. Preferable to have large flashing arrow signs at the entrance to the single file, one on each side equally spaced. And to have the warning sign upstream which says “zipper merge ahead”.
    Please have crews try this. It will work if you can obfuscate which final Lane people will end up in.

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