The orange highway sign with black letters holds a familiar warning: “Lane closed ahead.”
What do you do?
If your instinct is to immediately get out of the lane that will be closing, you may think you are being courteous to fellow drivers by reacting early — but in reality you could be slowing traffic, experts say.
It may sound like a breach of etiquette to wait until the last minute to merge, but traffic engineers and transportation departments in several states are promoting that exact move, sometimes with mixed results as they try to overcome drivers’ ingrained habits.
The maneuver is known as the late merge — or zipper merge, for the way that cars taking turns getting into a lane resembles the teeth of a zipper coming together. The move, in which drivers in dense, slow-moving traffic remain in the lane that will be closed and then pull into the other lane at the merge point, helps ease congestion and drivers’ frustrations, experts said.
As Tom Vanderbilt, the author of “Traffic: Why We Drive the Way We Do (and What It Says About Us),” noted, “Merging late, that purported symbol of individual greed, actually makes things better for everyone.”
Colorado started to promote the late merge during a highway project more than 10 years ago. Signs were posted, starting 2 miles from the point of the lane closing. The first signs read, “Use both lanes during congestion.”
The next signs said, “Use both lanes to the merge point.” When the lane was ending, the last signs read: “Take turns. Merge here.”
The result? A 15 percent increase in the volume of cars moving through the work zone and a 50 percent decrease in the length of the line, K.C. Matthews, a traffic specifications and standards engineer at the Colorado Department of Transportation, said in an interview last week.
The approach is effective in slow-moving traffic, and it allows drivers to take advantage of the lane that is about to close. In less-dense, free-flowing traffic, there is less need to rely on the late merge, officials said.
A work zone engineer for the Kansas Department of Transportation, Kristi Ericksen, said in an email that officials would customarily expect in work zones to see “large differences in the speed of traffic (nearly at a standstill in one lane and highway speeds in the adjacent lane) and road rage (rude gestures, eliminating gaps, lane blocking).”
Since the late merge was introduced, the queues for those two types of lanes are about half the length that officials expected, and drivers take turns at the merge point, she said.
“As for traffic flows, the data suggests that while the speeds are lower and the travel time may not be shorter, traffic continues to move and is predictable,” she wrote. “In other words, the travel conditions are more reliable, which has its own set of benefits.”
But when people apply their “off-road sensibilities” to their driving, the late merge can be harder to manage, Vanderbilt, the author, said in an interview last week.
For instance, a person would be considered rude if he or she walked to the head of a line of customers waiting for a bank teller. A driver in a free lane who zipped to the merge point and then tried to cut in could be judged similarly. Some drivers then take it upon themselves to become traffic monitors, enforcing societal norms and straddling the lanes to block those who might try to get ahead, he said.
“In a car moving at a certain speed, when the moment comes to make a quick decision, we may become more interested in getting into a battle for progress,” he said.
When the Minnesota Department of Transportation tried to promote the zipper merge, officials found that some drivers in the lane that was going to end kept pace with the car next to them “whether acting out of perceived courtesy or a sense of vigilante justice,” Vanderbilt wrote in his book.
The result was confusion and congestion. Quoting the puzzled Minnesota transportation officials, Vanderbilt wrote, “For some unknown reason, a small number of drivers were unwilling to change their old driving behaviors.”
Officials report mostly positive feedback from drivers about the late merge, although some occasionally take a dim view of it. Matthews recalled a Federal Highway Administration official who was in her own vehicle and driving through a lane-widening construction zone in Colorado. She was excited to see a zipper merge in action and zoomed to the merge point in the lane that was to end.
Another driver, who was apparently not as impressed as she was, threw a burrito at her car, he said.