Isn’t it obnoxious when a driver waits until the very last second to merge? According to a number of states’ traffic laws, it’s actually the best strategy.

While the commonly-named “Zipper Merge” may seem counterintuitive, a growing number of experts have argued that the merging strategy helps keep traffic flowing more smoothly and safely. A growing number of states, including Kansas, Utah, Missouri, and Washington, have begun to require drivers to use it in recent years.

However, many drivers misunderstand what a “Zipper Merge” is, and many may be confused about how Texas traffic laws handle merging at all.

What is a “Zipper Merge”?

According to the Kansas Department of Transportation, a “zipper merge” happens in a lane closure or lane-ending situation when drivers use both lanes of traffic up until the defined merge area, where they then alternate turns in a “zipper” fashion into the open lane.

“When traffic volumes are heavy and traffic is moving slow, it is much safer for motorists to remain in their current lane until the point where traffic can orderly take turns merging,” said Kansas DOT on its website.

The department noted that congestion is a frustration that all drivers share and that they should be considerate in taking turns while merging and allowing merging space for other drivers.

“Research has shown that this method is safer and helps to keep things moving more smoothly through the merge point because drivers are cooperating and creating gaps, thus eliminating brute force injections into the through lane,” the Texas Highway Man wrote in a blog post. “It’s those sudden, unexpected forced merges, especially from a standing stop, that causes shock waves in the traffic flow that creates the stop-and-go conditions often seen in these situations. When people take turns and know that’s the expectation, they can gradually open a gap earlier while still moving. Drivers in the closed lane can predict where they’ll merge, align themselves, and merge smoothly without having to stop.”

The Texas Highway Man went on to note that another advantage of the strategy is that filling the closed lane can prevent “opportunistic drivers from taking advantage of an empty lane to cut in the front of the line.”

However, he also contended that when traffic is free-flowing, it may still be best to merge early to avoid forcing drivers in the through lane to slow down and allow others to merge at the last second. Both the idea that the zipper strategy works best in congested traffic, as well as the benefits of avoiding more sudden forced merges, were also promoted in a blog post from the Texas Department of Transportation in San Antonio.

Studies conducted by the Colorado Department of Transportation showed that the zipper strategy can reduce delays by up to 40% in heavily congested areas, and a 2008 study by the Minnesota Department of Transportation proposed the method could reduce traffic by somewhere between 40 and 50 percent.

What does merging look like in Texas?

TxDOT San Antonio published a long list of studies, officials and laws from around the US promoting the “Zipper Merge” method. However, it still seems largely unknown and unused in Texas and has not been officially adopted. Meanwhile, the Texas Transportation Code has more to say on the subject of right-of-way and yielding when merging onto multi-lane roads.

The Texas Transportation Code states that, on a roadway divided into three or more lanes providing for one-way traffic, a driver must yield to traffic on the left when entering a lane from the right. This means that when entering a Texas highway or freeway, drivers must legally yield to vehicles already driving on that road. While drivers already on the roadway might yield to those trying to merge in order to avoid a crash or as a courtesy, that isn’t a part of the law.

That statute also applies to regular lane changes on multi-lane roadways. While it doesn’t give much of a hint as to how early drivers should merge when a lane is expected to end, the law does say that it’s a merging driver’s duty to slow or come to a stop until it’s safe to enter a lane to their left.

If necessary, the Texas Transportation Code also says that a driver can enter the shoulder of a road while merging into traffic and accelerate there until they have a sufficient speed to safely merge to the left.

On the flip side, the Texas Transportation Code says that drivers on a frontage or service road to a freeway or expressway are required to yield to traffic exiting that freeway or expressway, even if there are no yield signs.

Altogether, whether using a zipper method, entering or exiting highways across Texas, drivers are encouraged to take account of the situation around them and, when in doubt, yield. More information on driving safety and laws in Texas can be found on the TxDOT website.