Passing the 'lane closed ahead' sign and cutting in line later may be best merge strategy
Have you seen the road sign “Right lane closed ahead, merge left,” but while you move to the left lane, other cars fly by you in the right lane? Then they duck into the left lane ahead of the cars in front of you, just before the right lane is closed?
Do you get mad?
Believe it or not, those drivers who “cut in line” may be practicing the best way to merge in that situation. It’s called a “zipper merge” because it works like the teeth of a zipper, and many states are studying the idea and the best road signs to explain how drivers should do it.
“When a vehicle slows down to merge early in heavy traffic situations, it puts all drivers in danger, slowing traffic down too quickly, leading to unexpected crashes and lengthy queuing of traffic,” said C.R. McLeod, director of community relations for the Delaware Department of Transportation.
When the right lane is closed ahead, if most drivers try to get over into the left lane immediately after seeing the sign, traffic in that lane slows and backs up past the point of that first warning sign. Other drivers approaching at higher speeds haven’t seen any warning sign and may have to slam on their brakes or veer into the right lane or may even crash into a vehicle in the left lane that’s traveling much slower or even stopped.
“These dangers are decreased using the zipper merge, and traffic backups can be reduced as much as 40%,” McLeod said.
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Along with decreasing dangers, a properly executed zipper merge helps traffic flow through the bottleneck.
“The zipper merge allows for everyone to move at the same rate, minimizing delays for all,” McLeod said.
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In the Detroit Free Press, reporter Mark Phelan said an increasing number of states including Michigan are encouraging drivers to use the zipper merge to decrease congestion.
“Yes, that means the driver you cursed for ‘cheating’ by driving by you in the empty lane after you politely merged to the through-lane a half-mile before the construction zone was helping traffic flow more than you. Sorry,” Phelan wrote.
Michigan State University associate professor of urban and regional planning Teresa Qu recommends the idea.
The Michigan State Police Department has long endorsed it, too: "When approaching a construction zone in which a lane is reduced, remember to use the zipper merge. To keep traffic moving, drivers should use both lanes, with drivers taking turns alternating into the open lane," the department said.
Why does zipper merge usually work better?
According to AAA, which provides roadside assistance, travel information and other services, “The best way to merge may surprise you,” as the company reported in a story in “AAA Living.”
“To many drivers, immediately using their turn signal and trying to merge into the next lane seems like the most courteous thing to do. The zipper merge can be interpreted as cutting in line. But research has shown that the zipper merge is more efficient because it uses more available road space for as long as possible — helping to keep traffic moving,” AAA said.
Research in construction zones has shown a zipper merge cuts down on the length of traffic backups.
“It improves safety by promoting similar travel speeds between adjacent lanes. And it helps create a sense of fairness and equity because all lanes are moving at the same pace,” AAA reported.
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McLeod said, “When traffic is heavy and slow, it is much safer for motorists to remain in their current lane until the point where traffic can orderly take turns merging.”
A 2021 study by the department of civil and environmental engineering at the University of Missouri-Columbia found that while not all states agree on using the zipper merge, “a significant group … are widely deploying such a strategy.”
“The reasons for doing so are due to the problems that have resulted from early merging such as wasted capacity, excessive queuing of the open lane, the potential for queues to grow beyond warning signs and queue jumping and the associated conflicts and safety risks. In contrast, zipper merge has the potential to reduce queuing and reduce conflicts at the merging area,” the university study reported.
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Zipper merge is not a perfect solution
In theory, the zipper merge is the best way for traffic to move through an area with a lane closure, but studies have found it doesn’t work well in all situations.
First, the process requires drivers to take turns at the merge point, which is hard to rely on when people are getting frustrated because traffic is backed up.
Second, in light traffic moving normal speeds, studies have shown that traffic flows more smoothly if drivers merge soon after seeing the “lane closed ahead” sign. That’s because if two cars traveling nearly side by side at a normal speed are approaching the bottleneck, one driver may have to slam on his brakes — either the driver in the left lane to allow the driver in the right lane to merge, or the driver in the right lane who suddenly runs out of road. And that can cause a chain reaction as approaching drivers also have to slam on their brakes.
“When traffic is moving at posted speeds and there aren’t any traffic backups, it makes sense to merge sooner into the lane that will remain open,” AAA said.
The University of Missouri-Columbia study said topics that need to be researched further include how to inform the public about using the zipper merge, the best signs to use and the best place to put the signs in relation to the lane closure.
“Public education is vital since many drivers either do not understand zipper merge or are averse to changing from the long-held practice of early merging,” the study said.
Drivers prefer using the zipper merge under lower traffic speeds and higher traffic flow conditions, according to the study, but simulator results show that it works under higher speeds and moderate traffic flow. However, the simulations depended on drivers being willing to take turns.
Signs that worked to communicate the zipper merge idea to drivers
A 2017 study by the department of civil engineering at the University of Nebraska-Lincoln cited a Pennsylvania Department of Transportation experiment with the zipper, or “late merge,” concept.
“This system was implemented as a means to reduce the road rage engendered between drivers who merge into the open lane early and those who remain in the closed lane and merge into the open lane near the front of the queue at the last minute,” the study reported.
Starting about 1.5 miles ahead of the lane closure, a series of signs were placed on both sides of the road, “Road work ahead,” “Use both lanes to merge point,” “Lane closed ahead” and finally, “Merge here. Take your turn.”
“Although it is not standard practice, the late merge is used regularly at work zones on freeways by one PennDOT district office. No problems have been reported with its use, and it seems to be well received by drivers,” the study reported.
The late merge increased the capacity of the merging operations by as much as 15%, the study said.
Mark Phelan at the Detroit Free Press and Michael Nyerges at the Cincinnati Enquirer contributed to this story. Reach reporter Ben Mace at rmace@gannett.com.
This article originally appeared on Delaware News Journal: Drivers cut in front of you with a merge ahead? It may work better
