New Mexico’s Zipper Merge Experiment Is Failing, Producing Pollution

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In theory, the “zipper merge” is a great idea. The road space in both lanes is utilized fully, and when it comes time to merge, people alternate and everyone gets where they’re going without a traffic jam. If everyone maintains a steady speed, leaves space between themselves and other cars, and everyone gets in at the last second, everyone wins. This was something I genuinely hoped to see succeed.

No plan survives contact with the enemy, though. I drove across four states that take different approaches to merging, and learned that the zipper merge doesn’t really work in the real world. It only leaves traffic stranded and idling on the interstate, creating a waste of time and increased pollution in its wake.

The New Mexico Approach

When I crossed into New Mexico from Arizona on I-40, we were already encountering our first construction zone. The signage for this began in Arizona, and I’m guessing that the proximity to the state line forced them to do things somewhat normally. People got over for the most part, and semi-trucks even split the lane to keep people from bunching up in the lane that ends. Traffic quickly cleared up and everyone got through the construction zone quickly.

The second construction zone had signs encouraging people to keep using both lanes and “take turns at the end.” I recognized this as a directive for people to try the zipper merge, and figured that with enough direction from the signs, it might just work. I was hopeful, but this was when all hell broke loose.

The same exact vehicles that basically sailed through the last construction zone on the state line got jammed up this second time. Instead of keeping a steady speed and merging up at the end, both lanes of traffic were brought to a standstill, which only moved on into the construction zone at a very slow and painful pace. This continued over the course of the next 100 miles or so, as there were several other construction zones with signage encouraging the zipper merge technique, along with at least one billboard.

But hey, I figured, this was just one day on one road. “Surely I’ll run into another construction zone down the road where it would work well,” I said to myself. Even late at night further east in the state, zipper merge signage snarled up even the lightest of traffic and left most of us emitting pollution for nothing.

The Texas Approach

The next morning in Texas, I saw that it wasn’t trying what New Mexico was trying. There were several construction zones in the panhandle, none of which clogged up, despite very similar traffic levels to what I’d seen in New Mexico the day before.

The Oklahoma Approach

Oklahoma does basically the opposite of what New Mexico does. It gives more advanced warning of the upcoming closed lane, and as the end approached, there was a “Do Not Pass” sign. After that (but before the end), there was a sign saying “State Law – Merge Now.” This led to only one traffic jam, and that was in rush hour traffic near Oklahoma City, so it’s not a good comparison.

Everywhere else, people were able to get into the zones, get through, and get out with very little in the way of traffic problems. It was smooth sailing.

Arkansas Takes This Further

As I-40 went into Arkansas, I saw that it was taking this one step further. For as many as 7 miles before a closed lane was coming up, there were big digital signs warning of the coming merge. As the merge approached, there were signs encouraging people to go ahead and merge as early as possible, which nearly everyone did.

The only traffic jam I encountered at any point along I-40 in Arkansas was when we got to the state line with Tennessee. At that point, I-40 is closed entirely, and vehicles have to go on I-55 to get across the river due to an aging bridge that suffered a structural failure.

Once again, the evidence seems to indicate that the zipper merge is hogwash.

Why Isn’t The Zipper Merge Working?

With all of the experts I’ve seen over the last few years claiming that the zipper merge was the superior choice, my real world experience with it failing doesn’t make a lot of sense. Given New Mexico’s particular stubbornness about this, surely it has studied this out in some fashion, and found good evidence for its approach. So, why did it fail?

First, I tried to find video of successful zipper merging so I could see if it works somewhere. All I could find were various computer simulations, animations, and even video of people wearing weird car costumes doing a zipper merge. I did find one video of what appeared to be a successful zipper merge, but it was still very slow and awkward, and only a small handful of cars did it. On YouTube, I did find a great number of examples of it not working out.

The obvious answer is to blame the drivers, but I have to question the wisdom in that. If a merging system is designed to work on a road with real drivers, and too few of the drivers participate to make it work, then that’s not an argument in favor of zipper merging’s success. It’s more evidence that it doesn’t work in a particular place.

I’ve similarly seen many comments on YouTube videos saying that it works in Europe, but no videos of it working in practice. Even so, the average European driver gets a lot more training and scrutiny than the average American driver, and Europeans tend to be culturally very different from Americans, leading to very different outcomes.

As I’ve pointed out several times, I was hoping to see it work as advertised by the experts, but my experience and then subsequent attempts to find it successfully working somewhere doesn’t give me a lot of hope for it at this point.

Have you seen it work well somewhere? Or can you find a video of it working with real drivers in real cars on a real road? I’d love to hear about it in the comments so I can learn more.

Featured image: Screenshot from NMDOT’s Zipper Merge campaign website. Fair use, commentary.


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Jennifer Sensiba

Jennifer Sensiba is a long time efficient vehicle enthusiast, writer, and photographer. She grew up around a transmission shop, and has been experimenting with vehicle efficiency since she was 16 and drove a Pontiac Fiero. She likes to get off the beaten path in her "Bolt EAV" and any other EVs she can get behind the wheel or handlebars of with her wife and kids. You can find her on Twitter here, Facebook here, and YouTube here.

Jennifer Sensiba has 1902 posts and counting. See all posts by Jennifer Sensiba