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Dynamic Zipper Merge


​​​​​​​​​In 2019, the N.C. Department of Transportation introduced new technology that has reduced backups in work zones where two lanes of traffic merge into one lane. The technology, called a Dynamic Zipper Merge​, also has improved safety by warning drivers of any traffic slowdowns or stops as they approach the work zone.

How It Works

​​The Dynamic Zipper Merge relies on a series of speed sensors set up on the side of the interstate for several miles before drivers must merge into a single lane. The sensors gather data about traffic congestion and then feed the data to message boards that change the signs that drivers see based on the traffic patterns approaching the work zone. In addition, the department's Statewide Transportation Operations Center also monitors the zipper merge system.

Depending on traffic conditions, the messages may indicate, for instance, "Slowed Traffic Is A Mile Ahead", or that "Traffic Has Stopped 2 Miles Ahead."

In certain conditions when traffic has slowed or stopped, the message boards will indicate “Use Both Lanes/To Merge Point." At the start of the work zone, the signs will display “Merge Here/Take Turns." As its name suggests, this type of merge is intended to work like a zipper. By taking turns at the merge point, drivers experience smoother merging conditions, which reduces traffic backups and the amount of time it takes to go through the merge.

The innovative merge system reduces the confusion between drivers who think they should merge early versus those who want to use the open lanes for as long as possible.

Where the Technology Is Deployed

In the spring of 2019, NCDOT installed the system at a total of four work zones, all west of Winston-Salem, that required long-term lane reductions for highway reconstruction. The department worked to fine-tune the system after installing it in one of these work zones at a time:

  • I-40 East in Davie County
  • I-40 West in Davie County
  • I-77 North in Yadkin County
  • I-77 South in Yadkin County

​​​​​After the system was installed on I-77 North in March 2019, the length of backed-up traffic had been reduced to about 2 miles; before the system, the maximum length was 8 miles long.

Future Considerations

The Dynamic Zipper Merge system does not work for every work zone. Because of the complexity of setting up the sensors, the system functions best for highways with travel lane reductions that will last for several months and cause significant delays. Engineers at NCDOT are evaluating where else to deploy the system in the future.​

6/15/2021 3:52 PM