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Taking Turns: What Is A Zipper Merge?

Written by Tom Crosley
Sep 05, 2019 Car Accidents, Texas Law, Vehicle Wrecks
  1. 1. Lane Closures Are a Part of Commuting Life
  2. 2. What Is a Zipper Merge?
  3. 3. Zipper Merging Can Reduce Traffic Bottlenecks by up to 50%
  4. 4. Shorter Wait Times May Cut Down on Road Rage and Aggressive Driving
  5. 5. Why Isn’t the Zipper Merge Part of Texas’ Traffic Laws?
  6. 6. Crosley Law: Fighting for Car Accident Victims in San Antonio

We’ve all been there: you’re approaching a lane closure, and you’ve already merged early so you don’t have to inconvenience anyone. Suddenly, a car zips by in the closing lane, passing by dozens of cars and trucks. They get all the way to the merge point, squeeze in, and avoid the wait. Watching someone do this feels like watching someone cut in line, and you’ve probably muttered some choice words at the offenders.

Prepare to have your world turned upside-down: by merging early, it’s you that’s making traffic worse, and those late mergers are actually doing exactly what traffic authorities want them to do. The Texas Department of Transportation actively encourages late or “zipper” merging in lane closure situations.

Keep reading to find out why zipper merges are often safer and faster for San Antonio drivers and how they can reduce the number of car crashes due to aggressive driving.

Lane Closures Are a Part of Commuting Life

At any given time, there are thousands of active road construction projects in Texas. When you add breakdowns and car crashes to the mix, drivers frequently encounter lane closures.

Unfortunately, many of us aren’t sure what to do when we need to merge, and the results can be dangerous. In 2018, unsafe lane changes caused at least 37,766 crashes in Texas. Another 37,719 crashes happened because drivers were operating in multiple lanes at once.

RELATED ARTICLE: The Top 5 Things You Need to Know About Pile-Up Crashes in Texas

What Is a Zipper Merge?

In a zipper merge, all the drivers in the lane that’s closing continue to drive forward until the very end of their lane. The point where the lane ends is where all the merging occurs in a proper zipper merge. At the lane closure point, each driver from the non-closed lane stops to let one driver from the closed lane merge, then continues.

“by merging early, it’s you that’s making traffic worse, and those late mergers are actually doing exactly what traffic authorities want them to do.”

If you watched the process overhead from a helicopter, this type of orderly one-by-one merge would look a bit like the interlocking teeth of a zipper on a jacket coming together to form a single line, which is where the name comes from.

Zipper Merging Can Reduce Traffic Bottlenecks by up to 50%

According to multiple studies, zipper merging significantly and consistently reduces traffic slowdowns. A 2008 report from the Minnesota Department of Transportation based on electronic detection system data at highway construction sites found that consistent zipper merging reduces wait times by 40–50%.

Once you start to think about it, late merging makes sense. Rather than bunching up in a single lane as soon as possible, drivers can take advantage of two lanes for longer. However, the zipper merge only works if the majority of drivers buy into the system. One angry driver blocking or straddling the closing lane can grind everything to a halt and create a hazardous situation.

RELATED ARTICLE: How to Handle Aggressive Drivers and What to Do in A Crash

Shorter Wait Times May Cut Down on Road Rage and Aggressive Driving

Research also suggests zipper merging can cut back on stress, aggression, and road rage. Between 1999 and 2001, researchers from Texas A&M’s Texas Transportation Institute (TTI) studied aggressive driving and bottlenecks. In a phone survey, the research team reported that almost 51% of survey respondents said they were significantly stressed when other drivers prevented merging in a bottleneck. Another 37% reported high stress levels when another driver blocked them from moving out of a closing lane.

The researchers at TTI noted that high stress levels correlate with aggressive or selfish driving maneuvers such as straddling lanes, blocking a closing lane, or refusing to let merging traffic in. In the worst cases, drivers can succumb to road rage and intentionally try to harm other motorists.

The TTI study suggested that the Texas Department of Transportation explore zipper and late merging as an option to reduce stress and aggressive behaviors. However, the researchers did caution that zipper merging doesn’t yield significant benefits unless the majority of drivers follow the system.

Why Isn’t the Zipper Merge Part of Texas’ Traffic Laws?

Texas has tested zipper merging in some construction zones for more than a decade. Recently, the Texas Department of Transportation implemented zipper merging during construction on I-35. The agency has also tested the system out during several other major road construction projects in the past few years. In these designated zones, all drivers must follow zipper merging protocols and allow for late merging.

Still, there is no state law in Texas to date that strictly requires zipper merging in all construction zones — probably because many drivers have been merging early for decades and still get annoyed by people they perceive as late mergers, regardless of what traffic studies show.

However, you don’t need to wait until Texas updates its merging rules. You can encourage zipper merging and help make our roads and highways safer by yielding to merging traffic and avoiding aggressive behaviors like straddling or blocking a closing lane.

Crosley Law: Fighting for Car Accident Victims in San Antonio

At Crosley Law, we encourage all drivers to follow the rules of the road, exhibit responsible driving behaviors, and keep an eye out for merging traffic. Together, we can make Texas’ roads safer and less stressful for everyone.

Unfortunately, even the safest drivers can become injured when other drivers engage in reckless and negligent behaviors. When an aggressive or reckless driver causes a crash, you have legal options. To schedule your free consultation with an attorney and learn about your rights and options, contact Crosley Law by filling out our quick and easy online contact form or by calling 210-LAW-3000 | 210-529-3000.


Late merge… The zipper system. (2008, October). Minnesota Department of Transportation. Retrieved from https://www.dot.state.mn.us/trafficeng/workzone/doc/When-latemerge-zipper.pdf

New merging technique to be tested on I-35. (2017). My Interstate 35. Retrieved from http://www.my35.org/news/newsletters/2017/01/zipper.htm

Project tracker. (n.d.). Texas Department of Transportation. Retrieved from http://apps.dot.state.tx.us/apps-cq/project_tracker/

Texas Department of Transportation. (2018). Crash contributing factors. Austin, TX: Texas Department of Transportation. Retrieved from http://ftp.dot.state.tx.us/pub/txdot-info/trf/crash_statistics/2018/21.pdf

Walters, C., & Cooner, S. (2001, November). Understanding road rage: Evaluation of promising mitigation measures. College Station, TX: Texas Transportation Institute. Retrieved from https://static.tti.tamu.edu/tti.tamu.edu/documents/4945-2.pdf

The content provided here is for informational purposes only and should not be construed as legal advice on any subject.

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