CLARKSBURG, W.Va. (WBOY) — Drivers on Interstate 79 in north central West Virginia have gotten quite accustomed to merging into one lane on the highway, whether it be for road work or emergencies, but that doesn’t mean the process is quick and painless.

Some states use something called a “zipper merge” to cut down to one lane on multi-lane roads, but West Virginia prefers the alternate “early merge.”

Early vs Zipper merge

A zipper merge, also called a late or joint merge, uses both lanes of traffic up until right when the lane closure begins. Instead of merging early like is customary in West Virginia, zipper mergers use both lanes until the closure and then alternate which lane goes one car at a time.

Research on the zipper merge compiled by the Kentucky Transportation Center has mixed results, with some studies reporting that the merge helped traffic flow and others reporting no significant difference. However, a 2006 Michigan study reported that the late merge increased the average speed at the merge zone from 30 mph to 48.

In addition to possible increases in traffic speed, other benefits of the zipper merge include reducing the change of speeds from one lane to the other, making changing lanes “easier and safer,” according to problem-solving company Ayres. It also gives drivers a larger sense of equality since one lane doesn’t have the right-of-way over the other, and prevents obnoxious drivers from using the closing lane to cut the line.

By comparison, the early merge tells drivers several miles in advance that the closure is happening and recommends that drivers merge into the needed lane prior to the closure.

Why does WV use early merge?

WBOY reached out to the West Virginia Division of Highways, and a representative gave this simple answer: Zipper merges rely on driver participation. In order for the late/zipper merge to work, all drivers must be on board; one person preventing the merge ruins the entire operation.

Ayres said that this fault of the zipper merge can be fixed by simply not telling drivers which lane is closing, but in general, early merges are still favored in most of the country.

States that recommend the zipper over the early merge include Arizona, Indiana, Washington, Kansas, Missouri, Minnesota and North Carolina, and many European counties have been doing it for decades, according to the Hill.