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How Do You Merge? Early or Zipper?
Finally! Research that’s actually useful!
When you’re driving on the highway and you see a lane closed ahead, what do you do? Do you merge quickly into the other open lane? Or do you zoom ahead and try to merge at the last minute?
If you’re the former kind of person, the latter kind of person probably irritates you. Why don’t you just merge earlier, you may think, rather than being a jerk and trying to butt in?
Turns out, though, the rude mergers are (often) doing you a favor. From Ars Technica:
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.”
Here’s the diagram, in case you need it:
So it turns out that all of those rude late mergers were actually making things better, making them move faster. Who knew?
Now can we have some research on the reasons why people — especially in Los Angeles — take roughly 45 minutes to pull out when the light turns green?
Published in General
This may tie in with Louis Beckett’s post on individualism….
Like any decent pilot, I set up well in advance of the target zone, so I can concentrate on that when I arrive instead of trying to play catchup.
Eric Hines
I’m with Sam. You know whose job it is to keep society together? Mine. I pick my spot and then parallel it in the disappearing lane. Sometimes I’ll swing out of the through lane just to get this done. The video is like most studies — a poor simulation leading to the wrong answer. Perhaps the video poorly represents the study itself, which would not be a first.
Discussions like this put me in mind of dear old Dad, who died in 2007, and who I miss very much. Many things remind me of him. He was that sort of Dad.
Driving with him was always full of excitement, whether going forwards or in reverse (deeply imprinted in my memory banks are the 1970’s family adventures in backing up the 19-foot trailer which we towed to Prince Edward Island every summer, the day after school ended, and in which five of us, and one or two dogs spent the entire summer, only to arrive home at the last minute, the day before school started). To this day, I would rather stick forks in my eyes than reverse the car with our very small utility trailer attached, and I will go to almost any lengths to avoid it.
As Dad aged, his driving skills became ever more rudimentary and direct. I’ll never forget (it was the last time I went to England and didn’t rent my own car) my experiences getting onto and off the M5 motorway between Worcester and Birmingham in about 1998. (Keep in mind that we’re on the ‘other’ side of the road, and the entrance and exit ramps are all ‘wrong,’ and everyone’s travelling at about 90mph in cars the size of child strollers (pushchairs), so I am already a little freaked out . . . )
Dad getting on the motorway:
ME: “Dad, careful!” (as he tries to get in between two cars going at speed).
DAD: “It’s all right, he’ll just have to bloody well move over. I want to get on!”
Dad getting off the motorway:
ME: “Dad, careful!” (as car attempting to get on almost drives up our tailpipe)
DAD: “It’s all right, he’ll just have to bloody well wait. I want to get off!”
I really miss that version of England.
Little Story:
I was driving a beat-up 1967 Ford pickup when some dork in an Audi tried to fight me for the lane. I could almost hear his gasp when he realized I wasn’t going to move no matter how he crowded me. Go ahead, hit me — my truck will be fine.
“I’ll be battered and deep-fried [those may not have been my exact words] before I let him in,” I said. My lady friend sniffed and said “Well, I guess I was wrong about you.” “Oh, how so?” “I thought you were different. I didn’t think you were all macho about driving.”
I let that go for a while and said “Well, I guess I was wrong about you, too.” At length she looked over and asked how so. I told her “I never thought I’d hear you say you were wrong.”
Is there any research on why Southern Californians insist on driving 10-15 miles less than the speed limit in the far left lane?
What about the case where the lane in question doesn’t end, but instead continues in another direction, e.g. an exit-only lane or a freeway split?
In that case it seems clearer to me that the late-mergers are just trying to cut in line, and that slowing down to merge at the last minute (or worse, stopping to wait for an opening) is just blocking a lane and potentially creating a hazard.
Semi-related anecdote:
This morning, I was driving down a road with some (though not heavy) traffic… 2 lane road. I glanced in my rear-view mirror to see a middle-aged woman in a volvo convertable zip out a few cars back and zoom up to the car adjacent to me (it was a pickup hauling a trailer). She didn’t make it, of course, because we had all moved over to get around the slow vehicle. She ended up zipping back in a few cars behind me. A block later, she zipped back into the other lane to try to get ahead, again. So, naturally (by this point I was just having fun with her), I slowed to match the speed of the truck. She predictably swerved back in behind me. I passed the truck and on to the next slow-mover (my lane was moving faster, and patient drivers just waited it out) – she again tried to zip ahead but, of course, the space between slow-moving cars was not big enough.
Eventually, several of the cars ahead of me turned left (as did I), and I saw her chugging a large coffee drink as she passed….
This reminds of roundabouts. These things are popping up like dandelions in my region, and almost everyone hates them, but the DOT has “studies” that “prove” that they are better than 4-way controlled intersections. Except human beings in the real world can’t or won’t react like they are “supposed” to when approaching a roundabout, so accidents and back ups increase along with citizen frustrations.
All this goes to show is why self driven cars will increase life expectancy and improve the economy. From both decreasing stress and reducing traffic accidents, but also because the scientifically proven method will be employed therefore traffic will move faster and we will waste less time in traffic. However, it will also remove all the fun out of driving.
I actually heard a physicist talking about this on the radio years ago. He said the quickest and most equitable way for everyone to get through the bottleneck of an ending lane was to ‘use all the real estate’ – stay in your lane and merger zipper-style (as its called here) at the front.
The people who merge early are helping cause problems, not the least of which is providing an opportunity for people to jump the line.
I read once that “studies show” that there are more accidents in roundabouts — but fewer fatalities.
That’s because the deaths mostly occur when one car goes through the 4-way intersection at full speed and another car pulls out in front of it. Whereas with roundabouts you get more low-speed fender-benders, but usually everyone involved lives to tell the tale.
So I guess it depends which variable you want to optimize for.
It sounds like most of these problems resolve to bad road design and inattentive drivers.
It has always been self-evident, that in a lane reduction situation one should stay in one’s lane until it ends. It is generally better to stay in the lane that is being closed because some people merge early, getting out of the closing lane before they need to. This makes the lane that is open go slower in the backup. Zipper is the only way to go.
What seems to be missing from the comments (pardon me if I missed it) is that the problem with “zoomers” is not when a lane is being closed, but rather when they are forcing their way into a lane that is backed up. Say 100 cars are in line to exit, backing up on to the freeway. The driver that drives to the front of that line and forces their way in is essentially cutting in line. There is no zipper here as there is no lane being closed. It is a line pure and simple.
I tend to move over earlier rather than later, though it really depends upon which of the options seems likely to be the smoother transition.
Anecdote:
Last year I’m driving home from work and move over pretty early into a mildly congested lane. I found a good spot, so I was driving relatively fast. On my left (the closing lane) an SUV is coming up just a bit faster than me; it seems to be trying to put our two cars into exactly the same space at the same moment. I ease up a bit and let it in because I have much more room behind than in front of me, and I’m gaining on the cars in front. The SUV seems a bit familiar… I realize it’s my wife.
She recognizes me behind her at the light of the off-ramp and waves.
So here’s the view from the cab: It’s hilarious! I’ve watched people engage in something approaching mortal combat as they endeavor furiously to get home 7 seconds earlier if only they could just cut off that sorry jerk over there whose parents didn’t have any children that lived. My rule of thumb when driving a semi, is typically to leave plenty of room in front of me for people to get in. Then I watch in fascination as they ignore the three or four car-lengths I’ve left for them in front of my truck so they can speed ahead of a half dozen vehicles or so and then cut them off. Studies or not, it seems like studied asininity from my perch.
As for truckers running along side each other, typically they are talking on the CB and trying to prevent a great stampede of vehicles from rushing forward to cut others off. I’m not endorsing the practice, but that is usually the reason behind it.
My own philosophy when merging into a congested highway in my rig is to look for another 18 wheeler, since they will typically let other trucks in. Cars, not so much. As ever, I find the courtesies extended differ from one region to another, and so I have to adjust my own level of aggresiveness accordingly. There are places where kindness is seen as weakness that must be exploited. There’s a foreign policy lesson in there somewhere…
Somebody warn Jonah Goldberg. The Amish do use the internet!
One of the few things I can say I like about Europe is that in Germany it is mandatory to let someone in when they are trying to pass.. Seems to take the passion and competition out of getting back into a lane.
I drove a truck one summer back in the 60’s before going into the Marine Corps. Saw enough bad behavior towards truckers that I always make a point of letting a truck in if he signals that he wants to move over. EVEN if it means I hit the brakes. It is SO much harder to move a tractor-trailer over a lane than my Corvette. OTOH I get irked when truckers clog up the highway side-by-side. I don’t mind them passing – everyone has a right tto the road – but if you’re going to pass PASS for goodness sake! Don’t just sit there and scratch.
:P Not Amish just poor. The poor car hasn’t had an oil change since 2011.
On the plus side, a manual transmission works as anti-theft device. Someone tried to steal it last winter, only to discover they didn’t know how to drive it. They hit the wipers, the parking brake, and moved the seat around, but in the end, all they could steal was my ice scraper.
It appears to me that some commenters took a lesson from the quote that wasn’t offered. It didn’t say that traffic will move faster if both lanes are used to the merge point. It said back-ups will be shorter. 100 cars in one lane is 100 cars long, whereas 100 cars in two lanes is only 50 cars long. There are advantages in this, particularly on roadways where exits are closely spaced, but it doesn’t necessarily get you home any faster.
Some of the consequences of the early/zipper dichotomy do result in slower traffic flow, but that’s really a result of people being rude to those who use the opposite approach. I actually think this article endorses genuine courtesy. If traffic is moving well and you’re not going to cut somebody off it is not discourteous to change lanes wherever you like. If traffic is slow or at a standstill, the courteous thing is to take turns. Put another way, drive as fast as you care to without being dangerous or rude. Courtesy is rarely arbitrary.
My motto: Don’t be an aggressive driver, or a defensive driver. Be a conservative driver.
As someone with a CDL, I always flash My brights to let truckers in front of Me… then I whip around in front of ’em.
I’m a fan of the carpool lane when husband and I have to drive in LA and already looking forward to the implementation of the HOT lanes on the 110, 10, and possibly even the 405.
To assess the objective merit of a strategy, just check the rate of cars going through the single lane portion. Cars/minute at the choke is the only meaningful assessment of overall timeliness. individual or subjective merit (for time anyway) will probably have a different source.
If my boorish behavior profits me but detracts from the rest, why should I change?
It ain’t just Californians that do that. Trust me, from here in Tennessee.
I stay in the lane that is ending as long as I can. But I don’t rush to the end – I either match the speed of the car next to me or go just a little faster. I figure that way I will force both lanes to fill up all the way to the merge.
I figure this out on my own a long time ago. Early merging vehicles create what I call “nodes of instability” – whereby traffic must stop to let in the merger, which produces phantom braking behind in th eline, and which also then creates indecision of other mergers – making them they feel they should move over early like the other person, creating more instability. This creates multiple nodes for a significant distance along the merging lane, slowing traffic down. By having only one node of instability (directly at the merge lane) traffic can slow down naturally and alternate merging more efficiently. I keep on trying to tell everyone about it – but it’s a lost cause (light telling people they can make a dual turn left from a one way to a one way street).
Head fake, then gun it — judiciously — when all else fails. Usually after it appears the other person doesn’t intend to do me any favors. Zipper is the norm in Seattle, but you can never count on how much meth a person has had before getting on the road. Be on the lookout for drivers exhibiting their territorial imperative. Keeping a cool head is paramount in these situations.
Before exercising my last resort, I usually consider the relative age and condition of the paint of the respective vehicles. I love the good looks of my car, but it is a nine year old car and its paint has seen better days. Also, you have to take into account driver reaction time, car inertia, car response, braking response, how many targets you can keep track of in your head beyond your peripheral vision. Almost the skills of a fighter pilot.
Another thing to consider is that in WA state, they do have a minimum following distance, which is exactly one car length. If you can’t fit and you had to merge and there’s a collision, there will at least be some fault on the other party.
I suppose I should qualify Zipper being the norm in Seattle. Looking at the video, ‘zipper’ is the euphemism for the late merge. I Seattle we do have HOV lanes and there is a place at Northgate on I-5 where the reversible express lanes ends. When the express lanes are in use northbound, the southbound HOV lane ends at the express lanes. Electric signs advise from a mile before that the lane is closed ahead. Whenever there is a southbound backup in the main line, drivers in the HOV lanes get to scoot ahead of sometimes up to a mile of backup. HOV drivers want to merge as late as possible (‘zipper’), and though I-5 drivers in the passing lane are frequently happy to make room, occasionally some drivers, having already spent many minutes in a backup, will move to close up the space and hold the HOV driver from merging. That creates a situation where you, in the HOV lane, will compromise on merging as late as possible and just settle for the first available spacing that looks doable. You think that spaces have to open up, but you’ve got to be nimble to grab it.
A similar thing goes on anytime a single occupancy vehicle has cross a fast moving HOV lane to merge with the main line from an on ramp. Now you’ve got the interesting (and sometimes scary) situation or having to slow down — sometimes abruptly — to find your spot and merge, while you’ve got HOV traffic, including buses, barreling right behind you, but the mainline is st0p and go. This is typical of a merge onto westbound WA 520 floating bridge. The irony of this situation is that the HOV lane itself ends and has to merge into the two lanes going over the bridge in just an eighth of a mile, but everyone who has the right to use the HOV lane wants to exercise their right of way to the maximum and delay merging until they can ‘zipper’ it.
Merging from an on ramp does not allow a choice necessarily of where to merge, whether early or late. “Filling the lane” as it were — by waiting to merge until you’ve run out of acceleration lane for the on ramp — in this case almost certainly will lead to disruption in flow in the HOV lane.