A Story of Change Management and Psychology: The Zipper Traffic Merge


This is a great story for those interested in the psychology and challenge of change management. It involves something called the “zipper merge.” The zipper approach to traffic merging refers to the situation where two lanes reduce down to one lane and the volume of traffic is high:

  1. Cars use both lanes right up to the point where one lane ends (in other words, merging later rather than moving over earlier)
  2. At the point of the merge cars alternate moving forward into the one lane (the way the teeth of a zipper alternates between left and right when you zip up)
  3. If drivers in both lanes leave some space between themselves and the car in front, the zippering occurs even more efficiently as the level of braking required is reduced.
  4. If, however, traffic is light and moving at the speed limit, then drivers should merge early rather than use the zipper method.

Computer simulation models and, perhaps more important, real-life application has proven the zipper approach is superior but — and here’s where the psychology and change management come in — places that have implemented the approach have also struggled to have drivers “get it” and to consistently follow the approach. Consistency is key here because if a driver doesn’t get it then road safety (and sanity) are at risk.

An example is the Minnesota Department of Transportation that has actively promoted the zipper merge for several years. But in a story in June 2016 in Wired magazine, titled “Nice Minnesotans Don’t Get the Cruelly Efficient Zipper Merge,” the author noted:

One study after another proves the “zipper merge” is the best way to move cars from two lanes into one. Except in Minnesota, where people might be a bit too polite.

The idea behind the move is simple: If the right lane ends ahead, don’t move left as soon as you see an open spot. Hold off and make the shift at the last minute. It might seem rude, but it’s far more efficient in congested traffic. So efficient that the Germans, who of course practice it almost flawlessly, have a name for it: Reißverschlusssystem, or “zipper system.”

But Minnesota isn’t full of famously efficient Germans. It’s full of famously courteous Minnesotans, who don’t want to make anyone mad. The backups got so bad that the state’s Department of Transportation is teaching 3.3 million people how to merge.

The zipper merge cuts congestion by 40 percent, Minnesota officials say. It reduces the likelihood of crashes because everyone’s moving at the same speed, which is better than seeing a lane of slowpokes alongside a lane of leadfoots zipping past. But it hasn’t fully caught on in the Land of 10,000 Lakes, providing a lesson to Kansas and other states now trying to make merging moments more efficient.

Part of the problem is awareness. Not many states vocally encourage the zipper merge, so every newcomer has to learn the rules. But the other half is guilt and fear. “I don’t know if it’s a Minnesota thing, or an education thing, but people just do NOT zipper merge,” one sad driver wrote on a recent DOT survey. “And they get irate at the people who do. Seems that the choice is to either sit in line like a lemming, or do the zipper merge and endure the wrath of those who have been sitting in the line.” Another wrote, “Maybe it just feels wrong? I feel guilty about passing all those people and merging at the end.”

That’s a problem, because the zipper only works when everyone buys in. A single indignant driver blocking “late” mergers slows everyone down. DOT engineer Ken Johnson says the state has seen problems with “self-appointed traffic cops” who straddle lanes to ensure there’s no cutting.

The state had quietly promoted the zipper merge for nearly a decade before it decided to stage a full-out media blitz. In 2011, to convince nice drivers to do the efficient thing, Minnesota started peppering highways with billboards and instructive signs. It ran PSAs on the local news. It made YouTube videos. It claimed dothezippermerge.org and filled it with how-to’s.

It also cheated a bit, moving the “left lane closed ahead” signs closer to the closure. It made signs that say “begin merge, take turns,” right where it’s supposed to happen. That at least gets rid of any remaining confusion, liberating drivers who know to hold off merging from the guilt that comes with passing those who’ve already changed lanes. “People would prefer to merge late as long as they are given permission to do so by good signage,” says Leon James, a traffic psychologist with the University of Hawaii.

The effort worked, sorta. The Minnesota DOT’s latest survey, from 2012, found that 73 percent of drivers believe the zipper merge is a good idea, though it has no numbers on how that translates to actual driving. Another small survey found that after years of outreach, 49 percent of Minnesotans were at least “somewhat uncomfortable” zipper merging. In 2013, the Star Tribune noted the zipper is “still [a] tough sell for Minnesota drivers.”

“Unless something changes soon, the zipper merge is going to be this century’s conversion to the metric system in the 70s,” Minnesota Public Radio’s Bob Collins has written. “Great idea, made perfect sense, and was dead on arrival.”

Don’t give up hope just yet. Washington and Missouri have officially endorsed the zipper merge, and Kansas is gearing up to implement the move later this month. Yeah, the state is worried that Kansans will go all Minnesotan, says Kristi Ericksen, a DOT engineer. But the agency has already started its own social media campaign, complete with two wisecracking traffic cones. (“Zipper merge? I don’t have a zipper!”)

And there’s another promising figure, this one from Minnesota: That small 2013 survey found that 45 percent of drivers 25 to 34 are comfortable with the zipper merge, compared to just eight percent of seniors. The late merge has been incorporated into the state driver’s manual taught to beginning drivers, so even more excellent mergers are on the way. The future of driving, in Minnesota and Kansas and everywhere else, just might zip along.

Take note that Minnesota has been trying to implement the zipper merge for over 10 years. Signs instructing drivers to “Use Both Lanes,” to “Merge at the End,” to “Merge Here” (with a big arrow pointing at the spot) and to “Alternate” does not seem to have penetrated everyone’s skull. If you go to YouTube one can find tons of videos of outraged drivers who don’t understand the zipper merge and suffer road rage when other drivers try to follow the zipper merge rules in places like Illinois.





Some thoughts:

  1. It doesn’t matter how many times you think you’ve explained something, you going to have to continue to communicate — often in many different ways — the change you’re making. I used to have a section in my change management course called The Rule of 8 (as in you need to communicate things at least 8 times before it starts to get heard and acknowledged) but it’s probably closer to the The Rule of 8 to the Power of 2.
  2. Just because you have data, computer simulations, and spreadsheets doesn’t mean people will understand or buy into the change. Many business people continue to think that “markets are rational” and that “people will act in their best interests.” The zipper merge is better for everyone and yet that is not necessarily sufficient to make people change habits or beliefs. Everything has two components: a Technical aspect (e.g. the numbers, the technology etc.) and a Behavioral component (e.g. beliefs, values) and I see far too many organizations spend 95% of the time on the numbers and technology and then gloss over the issues of beliefs and values.
  3. Even when you do all the right things, most change takes a lot longer than anyone ever wants to think. Projects make assumptions about reaching objectives but if something requires people to change behaviors then you should really question the forecasts on when (and how) this behavioral change will occur.
  4. Some big changes can occur quickly, but in my experience it often is a change that piggybacks on (or hijacks) existing beliefs and value systems. This is an insight that is both potentially beneficial as well as destructive. (It can be destructive if the belief is something, such as a prejudice, that ends up as a way to turn one group of people on another group.)
  5. In some cases total, end-to-end re-engineering can achieve big change (assuming the underlying process technology is sound, which is not always a given). For example, if every car and truck on the road was a true, self-driving vehicle, then the zipper merge would work very well as intelligent machines would consistently implement the merge, greatly reducing back-ups (as well as reducing the need to expand roads since robots would drive in tighter formation, increasingly the carrying capacity of every existing road, not to mention greatly reducing the need for parking lots).