What is zipper merging? Use this method to drive through WA work zones safely

The Washington State Department of Transportation has hundreds of construction projects in the works.

Cities and counties across Washington state are also planning roadwork projects over the spring and summer.

These road repairs often lead to lane closures in work zones, requiring drivers to merge into other lanes.

In general, the best practice for mingling with other cars is to use the zipper merge method.

Here’s how it works:

What is zipper merging?

A method of maintaining traffic flows despite a lane ending, zipper merging allows traffic to continue without interruptions.

“Safe and efficient movement of traffic through the merging area approaching a lane closure depends on the ability of drivers to plan ahead, adjust their speed and merge smoothly into a safe gap between vehicles in the open lane,” the state Transportation Department said on its Work Zone Safety site.

“When drivers merge more like a zipper, where vehicles in both lanes come together smoothly — even if not at full posted speed — everyone can get through the merge much quicker,” the state road agency said.

Legally, the responsibility lies with the merging driver to get up to speed and into the open lane safely, according to the state Transportation Department.

It’s illegal for drivers in the open lane to actively block merging traffic and prevent others from getting over.

What’s the best way to zipper merge in Washing state?

The Washington State Department of Transportation has guidance on how to properly execute the zipper merge.

Essentially, drivers should wait until their last chance to merge before the lane ends rather than merging as soon as they have space, or worse, forcing their way into another lane before adequate space opens.

This eliminates the congestion caused by drivers merging too early and forcing others to hit their brakes.

Drivers in the open lane should leave adequate space between the car ahead of them, and allow cars in the closing lane to merge into that space.

Meanwhile, drivers in the closing lane should manage their speed and distance leading up to the lane end.

If done properly, this leads to a seamless transition that doesn’t cause traffic congestion.

Is zipper merging really safer?

Several studies and analyses have shown that zipper merging is the best method for maintaining traffic flows amid lane closures, even if both lanes are already congested.

While waiting for the last moment to merge may seem counterintuitive, it’s proven to work.

The turn-taking approaches takes advantage of all available road space and prevents backups, so long as all drivers cooperate.

In the past two decades, studies have shown that proper zipper merging can reduce traffic delays by 40% to 50%. Several states have even implemented the method into law, requiring drivers to use as much road space as they can.

The method also encourages drivers to maintain similar driving speeds across multiple involved lanes.