Zipper merging keeps traffic flowing during WA roadwork season. Do you know how?
AI-generated summary reviewed by our newsroom.
- Zipper merging reduces backups by up to 50% during lane closures statewide.
- The method uses both lanes fully and merges vehicles alternately at lane ends.
- WSDOT urges drivers to plan, maintain speed and merge late for smooth flow.
Summer is prime time for construction in Washington state. With hundreds of construction projects scheduled across the state this summer, routes are altered on many cross-state trips.
These projects lead to lane closures, requiring drivers to merge into other lanes.
In general, the best practice in this scenario is to zipper merge. But do you know how to correctly conduct a zipper merge?
How to zipper merge
The Washington State Department of Transportation has guidance on how to zipper merge.
A method of maintaining traffic flows after a lane ends, successful implementation of zipper merging allows traffic to continue without interruptions despite the increase in cars.
Essentially, drivers should wait until their last chance to merge before the land ends rather than merging as soon as they have space. This eliminates the congestion caused by drivers merging too early and forcing others to hit their brakes.
“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,” states the Washington State Department of Transportation website. “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.”
Legally, the responsibility lies with the merging driver to get up to speed and into the open lane safely. However, it is also illegal for drivers in the open lane to actively block merging traffic and prevent others from getting over.
Drivers in the open lane should leave adequate space between the car ahead of them, so drivers in the closing lane can merge into that space once their lane ends. 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 lead to traffic congestion.
Why you should zipper merge
Numerous studies and analyses have identified zipper merging as the best method for maintaining traffic flows when lanes close.
Even when both lanes are congested, the most effective method of merging the two with minimal impacts is the zipper merge.
Waiting until the last possible moment may seem counter-intuitive, but it’s proven to work. Waiting until the final merge point takes advantage of all available road space.
When all drivers on the road cooperate, zipper merging prevents backups, allowing for a turn-taking approach.
In the last two decades, studies have shown than proper zipper merging can reduce backups between 40 and 50%. In fact, several states have made the method into law, requiring drivers to use as much as road space as they can.
On top of maximizing road space usage, the zipper merge method also encourages drivers to maintain similar driving speeds between multiple lanes