Despite its rude reputation, merging later is better for moving along heavy traffic.

A more commonly known sign, “Thru traffic merge left” is detailed in the official Caltrans manual as needed when a lane is being dropped at the next exit.

A lane is closed ahead. You move over but other cars fly by and cut in before the bottleneck. It's frustrating but experts say it helps traffic flow.

Traffic A Federal Highway Administration study found which zipper merge signs worked best The study found that three signs ahead of a zipper merge could help drivers use the preferred merging method.

With the zipper merge, you stay in your lane and move over at the last second, with drivers from each lane alternating entry to the single lane. It’s the most efficient method of merging.

Maine has been promoting the "alternate merge" for 10 years with signs showing left and right lanes merging into one middle lane.

With the lack of general merging etiquette in the Pacific Northwest, why are so many drivers slow to pick up and use the zipper merge?

Despite its rude reputation, merging later is better for moving along heavy traffic.

With the zipper merge, you stay in your lane and move over at the last second, with drivers from each lane alternating entry to the single lane. It’s the most efficient method of merging.

With the zipper merge, you stay in your lane and move over at the last second, with drivers from each lane alternating entry to the single lane. It’s the most efficient method of merging.