DOT: 'Zipper merge' keeps highway traffic zipping along

Posted July 30, 2014

— One accident, one construction sign, sometimes even one set of flashing lights can bring a highway commute to a crawl.

Kevin Lacy, an engineer with the state Department of Transportation, says a little inspiration from the fashion world – and a bit of politeness on the part of drivers – could keep traffic moving faster when vehicles have to merge because of closed lanes.

As long as traffic is moving at regular speeds, Lacy says drivers should move into the open lane as soon as possible when a lane is closed ahead. When traffic backs up, however, DOT engineers are looking at a solution now in use in Washington state and Minnesota called a "zipper merge."

With the zipper merge, drivers use both lanes approaching a construction zone or accident site. Once they get to the point where a lane is closed, each lane takes turns allowing drivers to file into the open lane.

"What you'll see is that it will operate much more efficiently," Lacy said, adding that persuading drivers to take turns is easier said than done.

"You're going to have to get over that urge not to let people get in front of you, he said. "What I'm telling you is, allow that gap, keep things moving. You'll be better off."

DOT engineers are concerned about merging around more than just lane closures, he said, noting that they also are looking at tweaking lane-marking in interchanges to make regular highway merging easier.


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  • Jeepgirl03 Aug 1, 2014

    Funny how it isn't mentioned in the article but when I watched the news Mr. Lacy decided it was appropriate to blame the northerners on not knowing what zipper merge is. This is a new term to me but I have been doing this for years. My husband and I are both from 2 different states up north and we both lived out west for a period of time and northerners and westerners know about this as well as that slower traffic should stay to the right. We taught our boys this because they said it isn't taught in drivers ed. If people would stop paying attention to their phones or radios and obey the traffic signs and move over to the right hand lane where slower people are supposed to be and use this zipper merge all would be better on the roads. Stop blaming anyone who isn't from NC or the south and start educating people. Just the other day I saw a woman driving with a donut tire and she was in the middle lane on I-40 during evening rush hour traffic doing 55mph.

  • Wendy Banner Jul 31, 2014
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    This isn't anything new; they've been doing this for years in Germany!

  • misterprecedent Jul 31, 2014

    If people would merge as soon as they see the warning signs (instead of using the closing lane as a passing lane), there WOULDN'T BE a line of cars waiting to merge at the point of closure, and EVERYONE would keep moving. Those who wait to merge and race ahead so to avoid the clogging are the ones CAUSING the flow of traffic to stop. Move over early and keep things moving!

  • John McCray Jul 31, 2014
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    View quoted thread

    Didn't say the DOT was wrong, nor did I say that you were wrong, necessarily. I just said that moving over two miles in advance is not what causes the backups. Two miles should give the person in the closed lane ample time to adjust their speed and merge into an open spot. I also agree with what EZlikesundaymorning stated. Regardless, there are lots of people who don't see the larger effect of their actions. They don't understand the accordion affect that happens when they try to cut in front of someone in an already high density driving situation.

  • monami Jul 31, 2014

    I don't think that drivers here, in general, can overcome "that urge" to keep the other guy from merging in front of them. Maybe drivers license renewals should require a good manners tutorial.

  • sinenomine Jul 31, 2014

    The catchy term "zipper merge" in the title led me to believe that this article had to do with some revolutionary new idea. It doesn't. All it calls for is normal courtesy, which isn't all that normal. This plan has as much chance of working around here as the proverbial ice cube in the nether regions of the earth's interior. The adage in Raleigh is "Give a person an inch and he'll change lanes."

  • Scott Mace Jul 31, 2014
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    Not exactly... he described a situation where everyone else has merged, except for that one person expecting to zip along in the empty lane to advance their position in line, and force themselves into the open lane at the last second.... the one that makes NO attempt to merge until they're about to hit barrels.

  • Dea2 Jul 31, 2014

    This method works very well in Germany and other European nations. Here, too many people are just so afraid of anyone getting in front of them and possibly getting there first, that stupid crashes happen constantly. Traffic does move faster when people take turns at lane closures, and at other legitimate merge sites, like on and off ramps. People who get into lanes that they know are ending then force their way back into traffic are just rude, and they're the ones who cause most of the crashes in the area, not to mention most of the road rage with their rude and aggressive driving.

  • farm Jul 31, 2014

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  • 68_dodge_polara Jul 31, 2014

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    Oh man the speeding in parking lots is what riles me up more than anything it's so bad here in Durham. People don't you know there are likely to be children especially in grocery store parking lot's? If your a passenger and your driver is speeding through a parking lot kindly remind them that they could kill a child doing that. Saying something could one day save a life.