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State: Use lane space before ‘zipper’ merge

Rick Keniston looked ahead toward the largely empty lane on the right side of state Highway 14, just east of Interstate 205.

“It should be full of cars,” Keniston, regional traffic engineer for the Washington State Department of Transportation, said during Wednesday’s afternoon rush hour as vehicles inched slowly toward east Vancouver, Camas and Washougal. “Some of them get it, but not very many.”

WSDOT is joining other agencies from across the nation that want drivers, during heavy congestion, to change what is widely considered the courteous technique for highway merging.

Last week, the state installed three signs along Highway 14 eastbound urging drivers during congestion to wait until their lane ends before doing a “zipper” merge where vehicles alternate and come together like the teeth of a zipper.

Transportation officials say using all available lane space during congestion can reduce the length of backups by as much as 40 percent. The zipper merge also can improve safety by reducing speed differences between lanes and pare the potential for rear-end crashes triggered when a driver stops or slows to merge, even though there is plenty of pavement ahead.

“We want them to go the full length of the lane and then merge in,” said Celeste Dimichina, a WSDOT communications consultant. “We are encouraging people to wait until the last second to merge.”

Highway 14 eastbound is a prime location for a zipper merge, since two lanes enter the highway from I-205. The far right lane ends about 1,300 feet later, while the second lane continues for another 2,100 feet.

It’s still a tough sell persuading drivers that, in specific situations and conditions, they should hold off merging and instead wait until their lane ends.

It can be perceived as rude and arrogant for a driver to zip by vehicles stalled in heavy congestion and expect to be let into the queue when there is no pavement left.

Some drivers will close any gap in front of them and refuse to let the vehicle in. A few might even flash the No. 1 sign with the wrong finger. In extreme cases, cutting in at the last second can trigger road range clashes.

A WSDOT blog uses catch phrases, such as “Merge late and cooperate” and “Northwest nice,” with the second one potentially borrowed from the state of Minnesota, which has been preaching the virtues of the zipper merge for the past decade.

However, drivers should not use the zipper merge on auxiliary lanes, which join the freeway at one interchange but exit at the next.

One example is where two lanes join Interstate 5 southbound at state Highway 500. Some drivers use the auxiliary lane to pass traffic jams on the main freeway, only to come to a halt and inch their way in as the auxiliary lane exits, blocking drivers who want to get off the freeway at Mill Plain Boulevard.

“That is not a lane closure,” Keniston said, “so people should not be using the auxiliary lane.”

Zipper merges work best in high-traffic low-speed conditions where there is considerable room before a lane ends, much more than a typical highway onramp, or during road construction when a lane is temporarily closed. During regular traffic conditions, drivers should merge as soon as they can safely do so.

WSDOT spent about $5,500 to put in the three signs, one urging drivers to “Use all lanes during construction” and two instructing them to “Merge here when congested.” The state will try other techniques to encourage drivers to embrace the zipper concept.

“Social media is our biggest platform,” Dimichina said.

If the intricacies of the zipper merge are too much, the Highway 14 campaign will be relatively short-lived. WSDOT intends to add a third lane on both sides of Highway 14 between I-205 and 164th Avenue, with construction set for spring 2021.

“Until we add lanes, we are trying to maximize what we’ve got,” Dimichina said.


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