Seattle lane closures toyed with the ‘zipper merge’

The in basket: Petra Hellthaler heard a report on a KUOW radio show called “Here and Now” this month about the use of the “zipper” merge tactic, and highlighted a couple of Web sites discussing it. She knows of my campaign to get it signed and used at the Bremerton merge of highways 3 and 304. She said she’s all for it too.

One of the Web sites decried the use of what it called “the jerk merge” on a troublesome San Francisco highway, saying that forcing one’s way into a line of bumper-to-bumper traffic “may exacerbate the city’s already horrendous traffic problems.”

The other one,  on the Ars Technica Web site, says that the state of Minnesota “began openly advertising the zipper merge in the early 2000s” and “now Washington state has followed suit to encourage zipper merging … in the highly publicized construction zones in Seattle.”

Its article was headlined “The beauty of the zipper merge, or why you should drive ruder” and included the following, from Minnesota traffic engineer Ken Johnson:

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.”

One might think that the article about the San Francisco “jerk merges” would be an argument against the zipper, but it’s not. It’s the series of merges all along the backup that makes things worse, and makes tempers flare, not the orderly alternate merges where the one lane ends.

TV news was abuzz this summer about those Seattle freeway lane closures, but I hadn’t heard mention of the zipper in all that.

But if it was true, I wondered about the possibility of it migrating over here to the 3-304 merge. A study is under way of making that merge work better, with a public meeting coming up this year.

The out basket: News of the zipper movement catching on in this state hadn’t reached our Olympic Region. Spokeswoman Claudia Bingham Baker said, “I’ve not heard of us going to the type of system you referenced.

 “As regards zipper merging in general,” she added, “studies show that if traffic is moving well, it’s better to merge before you reach the end of the merging lane.  If traffic is moving slowly, it’s more efficient to continue down to the end of the merging lane, and ‘zipper’ into traffic there.” 

Claudia then referred me to Travis Phelps, her counterpart in the state’s Northwest Region, and he confirmed what Ars Technica had reported.

I’d call it a “toe in the water’ approach, as it was limited to the Seattle construction zones, was temporary, and official advocacy of the zipper merge was mostly by Twitter, he said. There were no signs posted depicting the maneuver.

Phelps said the practice worked with varying degrees of success during the multiple freeway lane closures in King County. “One of the big hurdles is it’s a cultural thing,” he said, “getting people to see that, ‘Hey he’s not being a jerk by using an open lane.'”

Claudia didn’t express an opinion about the wisdom of installing signs on Highway 3 calling for use of the zipper movement at 304 to keep traffic flowing better than it does now. I’ll do what I can to make sure the stakeholder committee studying the congestion problem there knows of the idea.


5 thoughts on “Seattle lane closures toyed with the ‘zipper merge’

  1. Travis, I’ve noticed more people are starting to do it on 3 and 304. It’s working well. Not as well as if Mayor Jarstad hadn’t complained when the intersection was built, causing the state to give Bremerton equal ‘standing’ as #3. That’s politics.

  2. Merging one and one ~ or zipper is you like ~ is how it is done and has been done for years in other countries. Learning to drive many many years ago in Canada we were taught to do that. Crossing the Lions Gate bridge going from 4 lanes to 2 was routine. Everyone knew what to do and what everyone else was going to do.
    The biggest problem with malfunction junction at 3 and 304 is the merging of lanes on 3. The signs indicate the right lanes are to merge to the left and as hard as you try the folks in the left lane are not going to let you in, it is as if you are being punished for your lane closing. A simple one and one approach would clear this up significantly. If only they would give it a try!

  3. If sleepyjean is having trouble getting into the left lane because drivers there won’t make way for her, I’m guessing she is trying to change lanes too soon. Merge where the right lane ends, not before. Drivers trying to get into the left lane before the right one ends contribute to the backup. The banking at the actual merge point allows me to smoothly join the single lane flowing through without causing anyone else to slow down.
    Road Warrior

  4. I have been doing my own version of the “zipper” merge for several years. I choose not to “race” to the end of the right lane, but rather “creep” at nearly the same speed as the left lane. In all my merges, I’ve only have one other left-lane driver force himself into the narrow space left of the merging lanes to insure that he was there first.

  5. You know Travis you make an excelant point on one of the problems with the merge right there, but you know another contributing factor is the fact that cars come to almost a complete stop until they get under that overpass and then they decide to punch the gas and spped up when they realize that there is nothing in front of them or those who decide not to pick up speed real quick rather they just ease into their speed and slowly get back up to 50 mph. I see it everyday working out there on the highway. I do not think the speed drops below 50, it might go to 40 but there is no reason to crawl at a slow speed. I know there is a yellow sign out there that has a suggested speed on it and I think it might be 40 but even if it is 40 mph, drivers should not have to slow way down. Do the zipper merge at the end of the merge and keep going and those people in the left lane should just leave enough space between cars to allow the next car to merge and the merging car should keep the speed up and not hit brakes the second you merge. Drivers standing on their brakes causes a real backup.

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