A zipper merge is a traffic merging technique where drivers use both lanes until the lane reduction point, then alternate merging like the teeth of a zipper. This approach is more efficient than merging early because it maximizes road space, reduces congestion, and minimizes the length of traffic backups.

In a zipper merge, drivers in the closing lane should continue to the merge point while drivers in the open lane allow them to merge one at a time. While it can feel counterintuitive, studies show zipper merging improves traffic flow and reduces road rage in high-traffic situations.