Zipper merge eases traffic - and your dilemmas

Zipper merge eases traffic - and your dilemmas

By Laurie Merrill / ADOT Communications
March 31, 2021

Does merging on the highway pose a dilemma for you?

For a lot of us, a “Merge Left (or Right)” sign triggers an inner debate: Should we politely do what the sign says and merge now, or should we wait to merge later – and gain more ground – but feel guilty for cutting?

The zipper merge system ends the debate and encourages drivers to wait until the last minute to merge – without guilt!

What is the zipper merge, you ask, and what does it have to do with ADOT?

Glad you asked! No, it’s not a new line dance or a carnival ride, but a traffic system that organizes how motorists merge when a lane closes.

ADOT has been using the zipper merge on various projects since 2016. Currently, it is being used on the Meteor Crater and Two Guns bridge deck replacement and rehabilitation project on Interstate 40 east of Flagstaff.

Okay, but how does it work?

Here’s how, according to AAA. The zipper merge is like a zipper on a pair of jeans. Just as the teeth of your jean’s zipper come together, the zipper merge keep traffic coming together, smoothly closing the lane.

Motorists stay in their respective lanes until the final merge point, which is efficient because it’s not leaving one lane empty. It 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 next lane merges, and so on. Like a zipper!

Additionally, ADOT is testing a “smart work zone” in the westbound direction of the I-40 project. It uses a dynamic merge system with electronic signs and sensors and can be controlled remotely. When traffic is light, the signs ask motorists to merge well ahead of the closure. When traffic is heavier, the zipper merge system kicks in and signs ask drivers to merge later. You can read more about it here.

Dilemma resolved!

For more information about the zipper merge, check out this classic ADOT blog.

To see photos of the I-40 bridge deck and rehabilitation project, visit the ADOT Flickr album.