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As it turns out, drivers who wait until the very last second to merge aren’t jerks after all.

An increasing number of states, Utah being the latest, have enacted laws that actually require drivers to wait until “the last second.” Other states actively encourage it.  

Why? Because it works.

The so-called “Zipper Merge” might seem counterintuitive. One could even argue that it is human nature to get angry at drivers who pull in front of them.

However, when it comes to construction zones, lane closures due to crashes, and other issues that block lanes during high traffic periods, experts say the zipper merge approach keeps traffic flowing better and is much safer.

“Study after study shows the ‘zipper merge’ is the safest and most efficient way to merge in work zones and heavy traffic,” says Kurt E. Gray, a director of driver training with AAA. “To do so, use all lanes fully until you reach the end of the lane, then alternate into the open lane. It does take some cooperation, but it maximizes road space and helps keep things moving.”

The Missouri Department of Transportation shows us how the zipper merge works in this amusing video featuring adults in cardboard cars. Here is a less-cutesy video from Arizona’s transportation department.

The Zipper Merge approach. (Arizona Department of Transportation)

When drivers anticipate, plan for, and (cordially) allow drivers to merge into their lane at the end of the drivable road, traffic continues to flow smoothly.

However, when drivers try to merge early, experts say it causes cars in other lanes to slow down, sometimes suddenly. This increases the risk of accidents, and also creates pockets of valuable, unused roadway ahead of them.

Zipper merging can reduce delays by up to 40 percent in heavily congested areas, according to studies conducted by the Colorado Department of Transportation. 

For now, and for whatever reason, California isn’t interested.

“Caltrans is aware of the ‘zipper merge’ but we are not studying or researching it. We are not promoting it to the public,” a Caltrans spokesperson told KTLA.