You’re approaching a construction zone and a sign tells you the left lane will end several miles ahead. Traffic is heavy, but you see an opening and move to the right lane. As you inch along, drivers to your left keep zipping by. Miles ahead, you finally reach the merge point and the left-lane drivers make their move. Your pulse quickens. You pull up tight on the car in front of you and refuse to let anyone in. Are you in the right, or are you fortunate that nothing escalated?
In light traffic, the merge is easy. But moving over early when an opening first appears fails in moderate to heavy traffic, where greater efficiency can be achieved by using both lanes as long as possible. Simple, right? Not at all.
Traffic experts largely agree that the best way to combine two busy lanes is a technique called the zipper merge. Drivers use both lanes until just before one ends, then merge like the teeth of a zipper coming together: one from this side, one from that side, hopefully with minimal slowdown.
When this expert-approved pattern is put to the test on highways, the outcomes are decidedly mixed. More states, however, are encouraging zipper merging and educating drivers — or even making it the law.
Driving is a complex task requiring focus. When things along the way — traffic lights, road conditions, weather — work to our advantage, all is well. When they get in our way, stress is the likely result. And when another driver is the source of that stress, it can turn to rage.
We call it road rage, and it’s a serious problem, leading to accidents and even violence. It can spring from something simple like someone’s tailgating us, braking too hard, honking, flashing lights to pass or neglecting to use a turn signal. But few things on the road seem as enraging as the merging described above. Merging difficulties account for over half of major auto-related causes of stress, according to research by the Texas Transportation Institute.
I posted a description of the zipper merge in a Facebook auto enthusiast group, along with a video illustrating the technique, and asked for public comments. Many said they would move into the through lane as soon as possible and were angered when others sped along until the last moment. Some vowed that they would run off the road anyone who took this route. One respondent said the best argument against the zipper merge in the United States was that too many dangerous fools carried pistols and were willing to use them.
Traffic experts are enthusiastic about zipper merging, and they have statistics to back it up. The Minnesota Department of Transportation cites four benefits: It reduces differences in speeds between the two lanes, shortens traffic backups by as much as 40 percent, eases congestion at interchanges and creates a sense that lanes are moving more equitably. The Texas Transportation Institute found that a zipper merge strategy delayed the onset of congestion at the merge point by about 14 minutes and cut the maximum line of cars by 1,800 feet.
Some states have made zippering the law. In 2020, Illinois mandated that its Rules of the Road handbook include the zipper merge. Violators who impede others from merging are subject to a fine.
“The law specifically states that each driver shall reduce speed and/or position to allow a person to actually merge,” said Sgt. Delila Garcia of the Illinois State Police.
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The North Carolina House passed a bill that would mandate the zipper merge when lanes merged into one. The bill, which has yet to pass the Senate, would also require that driver’s license and driver education handbooks include the zipper merge.
Representative Brian Turner, a Democrat, sponsored the bill. He commutes more than 200 miles from Asheville to Raleigh every week and spends a lot of time on North Carolina highways.
“Anybody who travels any great distance to get to Raleigh knows that the most frustrating thing on the road is someone going slow in the left lane,” Mr. Turner told a House committee, as quoted in The Citizen-Times of Asheville. “The second most frustrating thing is when we merge from two lanes into one and everyone backs up in one lane.”
If the bill becomes law, it may be difficult to enforce. But even without penalties, it might at least encourage drivers to employ the zipper merge.
For all these efforts, the behavior is still considered rude by many. They feel that drivers who continue in the closing lane are cutting in front of them, and many angrily refuse to make room, shaking a fist or even brandishing a weapon. There is potential for worse. According to the American Psychological Association, 30 killings annually are linked to road rage.
Road signs asking motorists to use both lanes to the merge point can help guide drivers to better behavior. The Colorado Department of Transportation found that drivers merged correctly before construction sites only when a number of informational signs were put up both well before the work area and at the merge point. One read, “Use Both Lanes to Merge Point.” Other states have begun to add signs as well.
Lance Aldrich, a Michigan writer who has railed against those who refuse to get in line early, said: “Americans are fiercely protective of their property rights. They see someone who slides in at the last moment as a trespasser trying to steal something that is rightfully theirs. Perhaps if the zipper method were taught from a very early age and shown to be for the common good it might work. But otherwise don’t even think about squeezing in ahead of me.”