Should you use the ‘zipper merge’ in Kansas and Missouri? What state officials say

When one lane of traffic is closed on a congested road ahead, many drivers will change lanes as soon as possible to avoid passing stopped cars and merging ahead of them.

For some, it’s a question of etiquette.

However, Kansas and Missouri transportation agencies say that merging right away and leaving lots of empty lane before the closure may actually be more dangerous in some cases.

Instead, those agencies recommend the “zipper merge.”

That means cars use both lanes as long as they can, and at the last second, when they reach the point where a lane is closed, they merge.

It requires drivers to coordinate, slow down and take turns. They pass by the closure in the single lane one after the other. It looks something like the closing of a zipper — hence the name.

While some drivers consider it rude to pass by cars that have stopped and move over ahead of them, highway officials on both sides of the state line say it reduces congestion in the open travel lane.

“Early merging forces traffic in the open lane to slow down considerably, creating back-ups in the open lane and frustrations for drivers,” the Kansas Department of Transportation wrote in a 2016 post on its website.

“By using two full lanes of traffic until the merge, you reduce the difference in speed between the two lanes,” the Missouri Department of Transportation wrote on its website. “The length of backups is reduced by 40-50 percent.”

How does a ‘zipper merge’ work?

According to the Kansas Department of Transportation, drivers should wait until their lane is about to end before merging in between cars on the open travel lane.

“When drivers see the ‘lane closed ahead’ sign and traffic backing up, drivers should stay in their current lane up to the point of merge and then take turns with the other drivers to safely and smoothly merge into the remaining open lane,” the department wrote.

“When traffic volumes are heavy and traffic is moving slow, it is much safer for motorists to remain in their current lane until the point where traffic can orderly take turns merging.”

The department also refers to this practice as a “late lane merge.”

When is the best time to perform a ‘zipper merge’?

Kansas and Missouri authorities agree that zipper merges are best used when traffic is congested and moving slowly.

When other vehicles are moving quickly, it’s safest to merge into the open travel lane before your lane ends.

That’s because when traffic is moving quickly, merging at the last minute may be more difficult and cause cars in the closed lane to stop entirely.

They then must merge from a dead stop, slowing down the open lane.

The Missouri agency recommends the so-called “early” merging during times of light congestion, and zipper merging when there is “heavy congestion with slowed or stopped traffic.”

Do you have more questions about driving in Missouri or Kansas? Ask the Service Journalism team at kcq@kcstar.com.