What is Zipper Merging?

Zipper merging, or dynamic late merging, is an approach that helps alleviate traffic congestion, reduces queue lengths, and harmonizes traffic. This technique involves using all available traffic lanes until the designated merge point. Vehicles then take turns merging into the open lane(s), resembling the movement of a zipper.

A number of states are adopting dynamic late merge systems, like zipper merging, to increase capacity and safety in work zones. This system’s benefits include shorter queues, better traffic flow and a reduced risk of rear-end crashes.

Zipper Merging
Zipper Merge

How Does a Zipper Merge Work?

A zipper merge system uses portable sensors to evaluate average vehicle speeds before the merge point. Using the traffic flow data (free flow, slow or stopped), real-time messages are displayed on boards leading up to the merge point, helping to even out traffic flow through the merge.
The zipper merge is often combined with a queue warning system for a more comprehensive solution.


A Zipper Merge System is beneficial for:

  • Any multi-lane highway and interstate work zone with lane closure(s)
  • Expected daily queues of a ½ mile or more
  • Routes with high truck traffic
  • Routes where topography limits the visibility of congested traffic

Benefits of Using a Zipper Merge System


    • Reduced risk of rear-end collisions
    • Less aggressive driving
    • Less work zone intrusions due to orderly merging

Increased Mobility

    • Studies show this system has reduced queues by up to 40% and increased traffic flow by 15%, as stated in this article by Autoblog
    • Speed harmonization

Time and Money Savings

    Bottlenecks are the biggest cause of road delays, per a Canadian Automobile Association study. A bottleneck in Calgary is estimated to have caused 1.4 million kg of CO2 emissions, 150K hours of delays, and $4.34M lost in productivity over one year. A better traffic flow helps alleviate these problems.


  • Remote management via our JamLogic software
  • Detailed equipment and event logging 
  • Automatic congestion alerting via text or email (optional)

Frequently Asked Questions About Zipper Merging

What is the difference between a zipper merge and an early merge?

A zipper or late merge is used during times of congestion, encouraging the use of two lanes for as long as possible and changing lanes just before the merge point. 

An optional early merge is sometimes encouraged during free-flow conditions and encourages merging well in advance of the merge point.

Is Zipper Merging safe?

Studies show that zipper merging uses the maximum roadway capacity available to maximize vehicle throughput, resulting in lower speed differentials between vehicles and greater safety in these areas.