Let’s talk zipper merge

Let’s talk zipper merge

By Julian Lopez / ADOT Communications
October 27, 2022

A shorter queue.

A lowered risk of rear-end collisions.

Increased roadway efficiency.

Those are some of the benefits of using the zipper merge, according to ADOT State Traffic Safety Engineer Kerry Wilcoxon.

Maybe you’re not familiar with the zipper merge? No problem, there’s a GIF embedded in this post that illustrates it and we can explain it, too. Motorists stay in their respective lanes until the final merge point, which is efficient because it’s not leaving one lane empty and uses all available lane space.

At the merge point, vehicles take turns merging. The car in one lane merges, and then a car in the other lane merges, then the car in the first lane merges, and so on. Just like a zipper!

ADOT first encouraged use of the zipper merge in 2016 during construction on Interstate 10 of the Davidson Canyon bridge east of Tucson. Currently, the zipper merge is in effect on Interstate 15 when traffic is queued in work zones. It is also considered on a project-by-project basis and research is done to determine when and where it will be most appropriate.

So, when you see a zipper merge in place, it’s OK to follow the signage and continue driving toward the merge point. There’s no need to change lanes far in advance, which would leave empty space in one lane, increasing the traffic delays and work against the zipper merge.  

If you do move over and find yourself in a queue of traffic next to an otherwise open lane, remember to be careful if you decide to change lanes. The traffic in the open lane will be moving much faster than you think and it may be hard to see those vehicles before it’s too late.  Finally, if you choose to stay in the queue, be kind to the folks in the open lane and let them in when the time comes. They are helping everyone get through the area a little faster.