Of all of the reasons for traffic snarls, impending lane closures bring out a particularly brutal combination of road rage and etiquette confusion. Most drivers know the pain of approaching two lanes in this situation; the left one is backed up much further because the right one will close in less than a mile thanks to, say, construction.

Which lane should a driver pick in this scenario? Steer to the left as soon as you see a closure notice and you'll almost certainly go slower; stay in the right and you'll catch stink-eye, honks, and even swerving drivers. Everyone is upset that you're about to essentially cut in line—an act that will require a tense, last-minute merge of your own.

Most driving schools and transportation departments in the United States don't instruct drivers on how to handle this situation or whether they must merge within a certain mileage, leaving this kind of merge up to the grace of your fellow, angry commuters. This week, however, Washington state joined Minnesota in sending a clear message to drivers: merge rudely. It's actually faster and safer.

“You don’t put your foot on the brake at all”

There's a name for it: late merging, though advocates prefer the term "zipper merging" because it doesn't have a negative connotation. According to Ken Johnson, a Minnesota State Work Zone, Pavement Marking, and Traffic Devices engineer, "We want people to merge at the point we’re asking them to, so it’s not 'late,' per se."

It works as follows: in the event of an impending lane closure, drivers should fill in both lanes in equal measure. Within a few car lengths of a lane ending, both lanes' cars should take turns filling in the open lane and resuming full speed.

If roads are clear enough that everyone is already driving close to the speed limit, zipper merging isn't as effective, but in the case of congestion, Johnson said that this method reduces backups by a whopping 40 percent on average, since both lanes approach the merge with equal stake in maintaining speed. "When the queue backup is reduced, the access points behind a work zone, like signals or ways to get on and off the freeway, those aren’t blocked," Johnson pointed out. "People have a better opportunity to get off or on the system at that point.

"I’ve been amazed at how consistent the flow is," Johnson added. "You don’t have to put your foot on the brake at all. You just coast ahead and take turns at the merge point."

The state of Minnesota began openly advertising the zipper merge in the early 2000s, even including its description in the state's driver's manual, but the measure didn't begin to widely catch on until a few years ago, thanks to a state-wide advertising campaign in both traditional and online platforms. Now Washington state has followed suit to encourage zipper merging as the result of highly publicized construction zones, particularly on bridges that connect Seattle to many tech offices (including Microsoft's campuses) in Bellevue and Redmond.

"There can be a weird idea going through people's heads of, like, 'Oh, these people are cheating, cutting in line!'" Washington State Department of Transportation representative Travis Phelps said to public radio station KUOW on Tuesday. "Well, it actually lets traffic flow if you can let folks in. Play nice. Treat traffic like a team sport. You gotta play the assist role. It's gonna help lessen the backups."

“People voluntarily leave a lane?”

Washington state has a ways to go to catch up to Minnesota's efforts, however. In particular, the Minnesota Department of Transportation has added sensors to key roads; when they recognize pile-ups and congestions, electronic signs turn on and tell drivers to fill both lanes and merge at a later point.

Johnson said that electronic, conditional signs have proven more effective than static ones, and he pointed to a study from 2010 which revealed that 80 percent of Minnesota drivers still considered themselves "early mergers." An advertising and public outreach campaign followed, and a follow-up study in 2012 showed a massive turnaround in thinking in which 73 percent of respondents thought zipper merging was a good idea after all. ("When we were starting the campaign," Johnson added, "we worked with an east coast advertising firm who said, 'Wait, you have people who voluntarily leave a lane?'")

The zipper's catch, of course, is that every driver on the road has to be aware of, and believe in, the style of merging before it reaches maximum efficiency. So long as enough drivers don't fill both lanes or intentionally block the soon-to-end lane in the form of vigilante car justice, the concept still has to contend with confusion, whether from out-of-town travelers or oblivious commuters.

"People have learned that it's polite to move over sooner," Johnson said, and that fact means his research and tweaking will continue for years to come to get his state—and hopefully others, as he's been consulted by other transportation departments—into a zipper-merging mindset. He encouraged other states to join in and advised them to try things like updated driver's manuals, public outreach campaigns, and partnerships with local law enforcement to stop lane-blockers.

This early on, at least, the results are clear enough for other states to take notice. The state's congestion reduction is easily measurable, and while crash reports can't be easily pinned to zipper-merging zones, Johnson is confident that "when both lanes travel at the same speed, we have fewer crashes across the board."