Does the Zipper Merge Help Traffic Flow?

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Does the Zipper Merge Help Traffic Flow?

zipper merge

A zipper merge is when cars in a lane that is ending take a turn to merge into the next open lane without stopping. A zipper merge is based on the idea that the cars in the open lane will slow down and encourage drivers in the closing lane to move into the open lane at merge points. In peak rush-hour traffic this might seem like an obviously good and safe idea. That is the theory and it relies on driver patience and courtesy. Let’s take a look at what the experts think. Here are some of the advantages and disadvantages of zipper merges.

Does the Zipper Merge Help Traffic Flow?

Experts agree

Experts agree that driving down as far as possible to the defined merge area and then taking turns to merge into the open lane is better and safer for traffic flow. In fact, traffic engineers also agree that the zipper merge, with cars from both the ending and open lanes taking turns one at a time to proceed, reduces accidents. One state has already made the zipper merge law and other states are set to follow suit.

Theory vs Practice

The correct way to operate is for cars in the closing lane to travel along with it and then merge seamlessly with the open lane at the place where the two lanes converge. Some motorists in the open lane think that cars in the closing lane trying to merge at the last minute are rather rude. They shouldn’t have any right to expect to be let in and do their best not to let them in. For some drivers, the zipper merge is a difficult concept to embrace. Consequently, it is difficult to maneuver in gridlocked traffic on the freeway. Most drivers consider zipper merging as pushing in and not as a logical, orderly, and safe part of traffic flow.


The idea is to have both lanes of traffic moving smoothly at the same speed which is vital to traffic safety. The zipper merge can relieve the congestion on motorways by maintaining a smooth, even flow of traffic. Another benefit is that it helps to control and maintain the speed at which a traffic jam moves forward. As a result, traffic moves fairly for all drivers. This movement relieves the congestion at intersections in town, near highway onramps, caused by cars wanting to get onto the highway. Furthermore, reducing the difference in speed between the closing and open lane zipper merge reduces traffic jam time by as much as 40 percent.


Driving on the highway in traffic involves human emotions. People can’t be trusted to be considerate of their fellow neighbors at the best of times, let alone during peak traffic times. Compliance is what the zipper merger needs and relies on to be effective. Another problem is well-intentioned drivers in the closing lane trying to merge ahead of where the lane is due to close. This has often lead to unexpected fender benders and even road rage incidents.

With all the drivers in the closing lane merging early, it leaves the closing lane empty for cars to drive down and then merge. Therefore, they appear to not want to wait their turn in the traffic and are trying to get ahead in the traffic jam. This has the effect of open lane drivers not leaving space for closed lane drivers to merge into. Upset open lane drivers accuse zipper merging drivers of being cutters, and that they are responsible for causing a chain reaction of drivers preventing each other from merging, thereby exacerbating the traffic jam backup.


Although open lane drivers probably have the right away, the safest thing to do is yield. The ultimate outcome is that we all get home safe and sound, and perhaps a little earlier.

Additional Reading:

Drivers, you’re merging all wrong: Being polite is causing traffic jams, experts say

Does Omaha know how to zipper merge?

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