Tom Vanderbilt's Traffic: Why We Drive the Way We Do (and What It Says About Us) contains the same conclusion that late merging leads to less congestion because of fuller utilization of available lanes. Related reasoning supports the London Underground's Holborn Station experiment to encourage escalator users to stand on both sides, rather than the customary stand-to-the-right, walk-to-the-left.
the stations where they encouraged people to stand on both sides were so far underground that almost no one chose to walk up. In the case of the Bay Area the “walking” side is often fully utilized and it wouldn’t make sense to stand on both sides.
BART now discourages "stand right, walk left" because it leads to "'uneven wear' on the escalator's gears, which can lead to more breakdowns and need for repair."
Maintenance problems aside, I'm usually surprised at how consistently people follow the stand-right "rule." Typically, everyone ahead of me followed it in my experience with BART.
Standing is denser than walking, so the throughput is greater (at the cost of latency, for those who would walk). I believe the station only encouraged the break in tradition at peak times, when there are significant numbers of people waiting to get on.
> Standing is denser than walking, so the throughput is greater
Doesn't this depend on the walking/standing density ratio and walking speed/escalator speed ratio?
Let say the walking density is 1/2 of the standing density. If the walkers walk at the speed of the escalator (i.e. their speed relative to the ground is 2x the speed of the escalator), then the throughput is the same.
Holborn's escalators are over 23 metres tall, as tall as a six or seven storey building. Very few people will walk up the entire escalator, essentially limiting utilisation to 50%.
There are other issues than eagerness to walk, like physical disabilities and collision avoidance. Ultimately two-speed traffic only works better if you're far from congestion, I believe.
We do this in the US in many places. The difference is we don't need a law for every common sense rule. And for some road configurations, strict adherence to the rule wouldn't make sense.
Alternating merging yes, but many people probably don't wait until the last possible opportunity to do so. Some merge as soon as they can and think late-mergers are trying to cut ahead.
That's because a lot of people like me don't/didn't know about the zipper merge and asscoiate it with 1 lane exits where assholes try and merge into the backed up exit lane after flying by everyone else in the other non queued lanes and thus blocking other lanes.
There's no worse feeling than realizing the backed up traffic in the right lane that you've been buzzing by was waiting for the same exit you need. I hate being "that guy" but sometimes ignorance catches you unaware.
Totally, that's why I let people in at the start of the queue and get more aggressive about not letting in people the further I get into the exit lane queue. I still let in people but the further into the queue I get, the less permissive I am because if you fucked up, then accept the fact that you will have to miss your exit and reroute back to your destination and hopefully you won't be that asshole next time and enter the queue early.
Using the road available to you is not "cutting" ahead. If anything, people merging before necessary cause unnecessary backup as use of the road is not being maximized, and therefore the slowdown is pushed further back.
I try to follow the zipper rule when getting on the freeway. The problem I run into quite often in CA (and the thing that frustrates me the most in urban driving) is when people behind me on a highway on-ramp cut across the solid white line to "get ahead". That then forces me to have to slow down while they pass so I don't ram them from the side. If you factor in other through-way cars already in the lane, this can really congest merging and you get major backups in the rightmost lane.
A similar event comes to mind when you come across someone sitting in the left lane going under the speed limit but completely unaware or bother for the people passing them.
So I guess my point is, while these are great in theory, they don't really work in practice without buy in from the herd (I use herd as this problem can be framed in a similar light as vaccinations and herd immunity).
Yes, this is one of those concepts which works much better for everyone, if everyone else drives like a German driver.
In the US, when you get to the end of the merge region, most people in the continuation lane will blast by at full speed, leaving no room to get over. I have to sit at the end of my lane, stopped, until I see a gap, and then floor it. That's worse for safety, fuel efficiency, wear and tear on my drivetrain, my own transportation time, and overall road throughput (everyone blocked behind me).
This is a "boil the oceans" type solution. All you have to do is convince everyone to do it.
Here, we can't even get people to stop blocking the box. The SPD is making short YouTube videos with "PRO TIPS" like "Bus lanes are for buses" [1] and "Don't stop in the street" [2]. The average driver is not at the point of thinking about higher level strategy like merge location yet.
Merging onto a freeway from an on-ramp is different, and zipper merge doesn't usually apply. There's a reason the merge zone is 300-500 metres long (where space permits), and depending on the region, clearly marked with a dashed line. It's up to you to match the speed of traffic, then signal your intention to merge before merging into a gap in traffic. Some on-ramps even have metering lights to space out incoming vehicles to make this process smooth. The only time other vehicles should have to change their speed is in heavy traffic, when a gap might not exist.
> Merging onto a freeway from an on-ramp is different, and zipper merge doesn't usually apply.
I'm not talking about merging onto a freeway from an on-ramp. (I'm told the relevant law for on-ramp merging right-of-way varies by state, in the US.)
> The only time other vehicles should have to change their speed is in heavy traffic, when a gap might not exist.
Heavy traffic is the only time a zipper merge might be relevant in the first place, no? In light traffic, just get in the correct lane whenever you want. It doesn't affect anyone else no matter where you do it.
In fast heavy traffic (when drivers aren't leaving the requisite 4 seconds between cars), there's no reasonable gaps into which to merge. Signaling my intention doesn't change anyone else's behavior, and I don't have the guts to sneak my car into a 20' gap at 60mph. Even if I make it, if the driver in front taps the brakes even slightly, we're all going to have a real bad day.
This is a perfect example of how you can't just transplant one aspect of German driving, in isolation, to American highways. On the Autobahn, nobody's driving full speed for an extended length of time at only 1-1.5 car lengths behind the car in front of them. It's reasonable to say "just merge into the gap" because they leave a gap to merge into.
Lane straddling doesn't prevent people merging via the zipper rule. Rather, it prevents people already on the road from moving over to the merging lane, shooting ahead of a bunch of people, then merging again (slowing down everyone else by adding to the merging traffic). It's one of those behaviors where whatever convenience that person gets is greatly outweighed by the cumulative cost to everyone else.
Actually lane straddling doesn't even work to prevent someone from using the zipper rule. It prevents people from passing other people on the right (nobody should be passing anyone on the right most of the time anyway). But it doesn't prevent someone from merging into the other lane when the time comes. As long as you're pacing yourself vs. the speed of the traffic in the lane you want to merge into, everything's fine. Using the zipper rule doesn't mean you race ahead of everyone before merging, if anything it means waiting a little bit longer and maybe even merging behind a car you would otherwise be tempted to merge in front of.
Straddling prior to zipper merge at the last moment is absolutely intended to prevent proper zippering, which you would describe as "shooting ahead on the right."
Maybe I'm wrong, but my understanding is that proper zippering is simply waiting until the lane ends to merge. You align the right side of your car with the curb and let it weave you into the lane at its own pace. It doesn't necessarily involve speeding ahead to get to that point, although certainly lots of people do that. It minimizes the jostling and speeding up and slowing down that people do to try to actively find a place to fit in.
When traffic is at its peak, it approaches its ideal state: the on-ramp is fully occupied with cars (no space wasted), and everyone's driving at basically the same constant speed up to the merge point, where everyone neatly and cleanly merges, alternating lanes. But if traffic is not at its peak, zippering doesn't require you to race ahead to merge point.
It wouldn't hurt anyone if you did that, of course. Same for everyone else waiting to merge. But there really are lots of people (where I drive at least) who are already on the road/freeway/whatever, who will move onto the (about to end) merging lane, race up to the end of it and force themselves back on the road, a few cars ahead. I've seen so many bad traffic jams made so much worse by people doing this. It makes a bad situation so much worse for everyone. Those are the people the straddlers are guarding against, not the well-mannered zipperers trying to do the right thing.
Your earlier comment misunderstands zippering (IMO). This one starts off less problematically but still ends with the wrong understanding:
> But there really are lots of people (where I drive at least) who are already on the road/freeway/whatever, who will move onto the (about to end) merging lane, race up to the end of it and force themselves back on the road, a few cars ahead. … It makes a bad situation so much worse for everyone. Those are the people the straddlers are guarding against, not the well-mannered zipperers trying to do the right thing.
This is basically incorrect. Regardless of how you and straddlers feel about this, using up that empty merge lane on the right is more efficient than straddling or other forms of early merging. That's my understanding, anyway.
The point of the article is that your intuition is incorrect. By inhibiting zipper merging you are forcing congestion backward, and leaving carrying capacity of the road unutilized during congestion when it is most at a premium.
Pushing congestion backwards is exactly the cause of a lit of traffic jams. I've observed this myself every single GD day on the 210W freeway between Hill exit and the 134 exchange. People get over way early, causing huge congestion to the merge entrances. If they'd stay left and zipper, everyone in the jam would save about 5-10 minutes. This is thousands and thousands of dollars a day of cost in completely avoidable congestion in just one two mile stretch of highway ( albeit it a particularly egregious one)
I'm not normally one to complain about downvotes but I literally cannot imagine how any of what I wrote was remotely controversial. Like I'm trying to look at it with different interpretations and perspectives and I'm just not seeing it. I've seen hotter takes in DMV driving guides. I'd be very curious what the disagreeing opinions are and why. For the record, I've never straddled lanes, I was just explaining why people do it.
In the ideal scenario of lane straddlers, everyone trying to enter a particular lane at a particular point has to do so at the end of the line of people already waiting to enter. The right hand lane is completely unused and therefore the length of the line is double what it needs to be, possibly so long that it interferes with other intersections.
In the ideal scenario of zipper merging there is no free right hand lane to shoot ahead in: it is completely filled with people that are alternately taking turns with the other lane to enter the merged lane. The queue is half the length in this case then the prior case. The lane straddler doesn't feel taken advantage of since everyone is entering the queue in the first available location (left or right).
Lane straddlers perform an illegal maneuver (I assume intentional driving in two lanes is illegal in most countries) to pre-empt the more efficient usage of the road. Their righteousness is unjustified: the person that would otherwise pass them in going to the front of the lane would be increasing the utility of the road. They would be more considerate by entering the lane they are blocking and going to the front themselves.
This sounds good in theory, but it works less than one out of four times. (no negativity bias included) There's always someone not following the rules, which in human nature automatically grants every observer to do the same. Following local news right now it seems people aren't even capable of "Rettungsgasse" (leaving a corridor for emergency vehicle access in traffic jams) anymore, a concept also encoded in law here. Sincerely, a German who's on the Autobahn on almost daily basis.
Strange. I see it working in practice 80% of the time... I’m on the road a lot, too. “Rettungsgasse” is something that regained popularity in the last years due to strong media push.
For what it's worth, foreigners driving there may not be aware of the rule. I tried as hard as I could to be a conscientous, informed road user before my first trip to Europe (studied signs, rules of the road, etc.) but still got an angry motorcycle cop whacking my mirror in France because I thought emergency vehicles would pass on the shoulder and had moved over to allow this, not in this Rettungsgasse (or the French equivalent)
What makes it worse is that the rules differ, even in EU countries. In Germany you have to make a 'Rettungsgasse' when there is a traffic jam, whereas e.g. in The Netherlands, emergency services use the 'vluchtstrook' (outermost lanes not used for traffic) in such cases.
Except where they've decided to let regular traffic use the vluchtstrook to drive on. Some roads you just need to be aware that you might need to make room for an emergency vehicle coming between the lanes.
That cop was probably angry for another reason, as Rettungsgasse are virtually unheard of in France. Emergency vehicles use the "emergency lane" at the far right of highways.
1 in 4 is better than 0 in 4, which is what most of the worlds traffic sees outside northern europe. I also don't really believe it is close to as bad as 1 in 4. Studies I have seen seem to say it works almost every time but maybe not perfectly so.
It’s much worse in my city in the US. People will actually block the lane that is closing forcing you to merge early. Especially if there’s a long line in the open lane. I had it happen the other day.
That is illegal and you can call the police and report them for it. I don't know if it will do any good but I've wanted to - if only there was a safe way I could do that while driving.
Are they driving at the same speed as the congested lane? That's how it should be done, in my opinion. If driving in the ending lane isn't seen as "getting ahead" and is seen as "using available road without cheating", the behavior could actually change.
No congested lane stopped, lane where the zipper merge would happen had at least a half mile of space before cones started forcing a merge. 5 or so cars behind me doing the same merge. I was traveling 15-20mph and decreasing speed.
> Following local news right now it seems people aren't even capable of "Rettungsgasse" (leaving a corridor for emergency vehicle access in traffic jams) anymore
The problem with the Rettungsgasse is that you only need one idiot to screw it up, but you often get many.
When I enter a traffic jam, I see most cars building it properly, but then I see one or two cars ignoring all others. I can understand that people might forget about it right when they arrive at the traffic jam, but once everybody arounds you do it, some just don't seem to get what's going on.
In other countries, like Austria, the Rettungsgasse is formed on the rightmost lanes, while in Germany, its on the left most lanes. Disparity of rules across EU countries doesn't help here either.
Also, for some reason, once the first police car goes through the Rettungsgasse, I often see many cars that just stop building it. Like "good job everybody, the police went through, we don't need the Rettungsgasse anymore!" even though there is still a jam. The ambulance comes 1-2 minutes later, and it has to fight its way through because of all these idiots.
In Germany the problem with the idiots is particularly bad, because while there are a lot of German idiots on the road, you also get a lot of international traffic with their international idiots on the Autobahn. If you learned to drive in a different country, chances are that you haven't even heard about this, and learning about all the different traffic rules of all the countries you drive through is a PITA.
Interesting. In the UK we have (or had) a 'hard shoulder' (extra lane unoccupied at all times) on our motorways and some trunk roads for this purpose. The government have decided to get rid of this by moving to what they call 'smart motorways' (repurposing that to a new lane) but without really properly implementing a similar rule change.
This is interesting, because merging in New York is an extremely aggressive and hostile activity on the surface, but with the equally high noise floor of ambient, surly stink eyes, each individual instance of road rage’s signal to noise ratio achieves a normalization that leaves all participants within the cloud-like traffic mob in a state of mutually unhappy compromise.
To reduce this concept to four succinct words:
Yeah, fuck you too...
In the outer tri-state area, and among tourists, this can, and does boil over into real animosity in the surrounding smaller towns and suburbs, where heavy police activity usually muscles up against aggressive city driving tactics, to keep the peace, and establish normitive boundaries to clue the unititiated in on the fact that they’s outside city limits, and it doesn’t fly in other counties.
But to elaborate, city merging means maintaining sub-six-inch proximity to adjacent vehicles in slow moving traffic. This is done to acheive a number of effects, from preventing pedestrian induced gridlock/deadlock at crosswalks, to nosing in on corners, such that a wedge forces surounding vehicles apart, by way of slow-motion chicken. It requires an extremely accurate sense of vehicle volume and the bounding box definition of your car’s footprint/shadow in the lane.
This manner of merging also plays into the fact that most professional drivers, from taxi cabs to box trucks, will yield, because they kind of get paid by the hour.
The only wrinkles to this driving style are Wall Street Lambos, McLarens and such, and the occasional motocycle. More often than not, these exceptions will often appear within proximity before you register their presence, and typically outmaneuver you, before you have a chance to assert position, even if you do see them coming.
In many cases the lanes weren’t designed for zipper merging or drivers “zipper merge” at inappropriate places. Zipper merge is great! But not all merging is to be a zipper merge- this is constantly abused, and perhaps justified in the minds of offenders under the guise of the zip. A lane, such as an entrance lane, that terminates is a good time to zipper merge. But many many times, in Minnesota, people use any lane that allows them to cut to the front of the line. Regardless if that causes a massive slowdown as they leave the relatively free flowing lane and “zipper merge” - match speed of the slow lane. Articles would do well to mention the finer points before ushering us to 10% gains... maybe.
The "merge when you can" mentality that has predominated in the US is the major cause of this. If people would just go down to the merge point and then merge there wouldn't be an issue.
It only leads to the perception of "cutting" when more idiots merge well before the natural merge point then logically where the lanes pinch back down.
Glad to see lane design mentioned, it's a key component. In most zipper merge opportunities there is a predominant lane and another lane that is ending, leading to the idea of a 'right' and a 'wrong' lane which precludes intuitive zipper merging. If lane design (even just the markings) were such that both lanes were equal prior to the merge, zipping together would seem the most natural thing to do whether signposted or not.
To encourage this behavior, why not put a stoplight in the middle of the road at the merge point?
Just like the ramp meters that limit cars entering the freeway. But instead a dual light that encourages zipper merging via offsetting green signals for each lane.
A full stoplight requires a full stop which defeats a lot of the benefits of a proper zipper merge where traffic just keeps flowing with no stops.
In a more general sense on a highway any time a car comes to a full stop you have the chance to create a phantom traffic jam as the stop travels back along the incoming stream of cars.
I think this is a dangerous approach, as the more aggressive drivers are more willing to play chicken and risk a collision. of course I follow the same rule myself.
Kiwis have this rule, signs saying "Take this tip: merge like a zip!" (think of it said in a happy kiwi accent). Driving in Australia without the rule, merging gets personal quickly.
I can't believe this is even debatable. Near my house there are a couple of lights where the road opens up to two lanes before the light, then after the light narrows back down to one lane.
Obviously people should zipper off before the light to load both lanes evenly and get as many people through the light before it cycles. Then after the light everyone should go forward and re-merge back into a single lane again.
Yet people will stubbornly pile into the left lane before the light leaving the right mostly empty then play games blocking people from merging in after the light.
Well, that's when they actually move through the light in a timely manner if not distracted from texting while stopped at the light :/
Yes, we have roundabouts where this happens. I also see this at the interstate on-ramp by my office.
There is a long lane, often backup up past a stop light and then it goes to 2 lanes for about 50 yards before the light that lets you turn left onto the interstate.
Nobody ever turns from the rightmost lane, everyone stays in the left lane. When I use the right lane and pass people I get angry reactions, people trying to block me from merging back in, and a couple times people cursing at me and following my car.
Sweden has the same laws, but everyone still merges early because some sense of "fairness" kicks in, and people don't understand that they're making any queuing worse by not utilizing all available road surfaces.
I've stopped caring about other people's sense of fairness in these situations, and I always use the empty lane and merge late. The law is on my side, and people can glare and honk as much as they like. I just saved five-ten minutes of not queuing, they could too if they all learned to drive correctly.
As a Brit, I always merge early due to the sense of fairness. However, this is strongly enforced by the nature of road signs, which show, say 500m ahead, a diagram with an arrow on the right merging to the left.
All it would take would be a consistent change of sign showing merging in turn at lane-merge to change this behaviour
The odd thing is that you do see very occasional zip-merge signs in the UK, which tend to reinforce the idea that zip-merge should any be used in exceptional circumstance.
As someone who lives in Ontario, Canada, I merge early as a defensive/safety measure.
People here will follow each other incredibly closely, even at high speeds, and quite often they won't slow down to let you in if you're trying to merge.
Personally I like to merge at the first opportunity its comfortable to do so to save me the potential stress and hassle of having to force myself between two cars at the last minute. But I've also never felt any animosity for people who pass me while I'm chilling in my lane.
I felt that way, and while you may have to wait a few cars, someone will always let you in. The likelihood of continual dickishness is limited by the multiplicative effect of independent events.
I independently rediscovered this driving in Southern California. It's the obvious fair and efficient solution for two lanes merging.
What most Americans have a hard time understanding is that German driving school, or Fahrschule, requires the student to master these "advanced" techniques. Unlike in the USA where if you can operate the throttle and the brakes you're good to go.
It's not just drivers who don't let someone from the empty lane 'cut in' - there are those that stop completely and let
in 3 or 4 'poor sods who were stuck on the wrong lane'. This breaks the system just as badly! The trick is to merge 1-1 as fluently as possible or you've broken everything.
I can see the comment in the post about the UK; I am used to this practice in a lot of EU countries I go; in the UK however, they don’t do this and the amount of roadrage there is quite staggering. I do not drive there but when I am in taxis/Ubers, the amount of honking, cutting in, swearing, (racial) insults and flipping the bird I have not seen in other countries. Ofcourse mostly in/around large cities but I have seen it in tiny villages too; enough anyway for me (YMMV) to think it is not an anomaly.
Not sure where all that anger comes from but I am happy that a hardly ever saw it in other countries where I drive or take a taxi.
I drove in Bucharest a few months ago; I did not notice this. But might well be as this is all anecdotal anyway; I have been in the UK many times, I have been in Bucharest once (I did not like it compared to other cities in RO).
I've never actually seen this work in practice, so maybe i'm missing something: Isn't the overall flow of traffic defined by the speed of traffic within the narrow section? E.g. if the speed limit and actual speed of traffic in the one- lane construction zone is 45mph, how people merge prior to that point should be irrelevant. The same number of cars are going to get through at the same rate.
From my experience, the speed is most often lower at the merging zone then in the following stretch of road. So overall througput could be improved by a more strict merging regime.
There are a few other things in play: You get less of the wave-like behaviour from 2 lanes merging. That means fewer start/stops. If the line is long enough, it may also reach the previous intersection - with two lanes it gets much shorter, avoiding blocking other directions.
I personally have never seen more efficiency on the road than Manila. Merging is just on an entirely different level in the Philippines. I would recommend going of course (not just to observe their driving) but there is no shortage of YouTube videos of traffic/Driving in Manila.
Or other countries in SEA, for that matter. The way to cross the road, as a pedestrian, in Cambodia is this: Close your eyes and, with one hand raised, walk across the road at a steady speed. Traffic will flow smoothly around you. Any attempt to avoid traffic by walking faster/slower will confuse everyone and lead to accidents.
In a case of a highway it might not be as beneficial, but imagine a city with lots of road intersections. If you put cars on two lanes and merge, you have half as long line of cars. In case of one lane scenario, the cars might block the previous intersection for other cars.
In a city, you won't have this problems, as traffic will jam at the first road work it encounter anway. Besides, how do ones plan to make all those people collaborate ?
No, it's the opposite. In a highway/motorway situation with more queuing space it's not such an issue.
In urban situations where queuing space is limited, using both lanes is more important, as longer tail backs will cause problems with junctions further back on the route.
The drivers should know to leave just enough space in front of them for the car on the other lane to merge. Having to stop for a merge makes everything slower. It takes longer to accelerate so longer to clear the jam. Ideally one lane slows down and leaves some spaces between the cars, and the other one merges 1 to 1 without anyone ever having to brake to a full stop.
And I see this working every day since where I live the rule applies. Of course there will always be the occasional smart guy who rides in the ass of the car in front in order to not let anyone pass and save 1-2 seconds at the price of causing everyone behind him 10 times the delay. This forces the cars trying to merge to come to a full stop, then forces some of the cars on the other lane to fully stop in order for the merging cars to be able to accelerate and merge.
Sometimes there is an unplanned need to merge, for example if one lane is closed due to construction or an accident (as I think is indicated in the video).
A lot of traffic has no blockage at the front, it's just the compressed bit of a longitudinal wave of cars, which creates a feedback loop of holdups behind it. Having space between cars allows the waves to dissipate more quickly.
This is not really specific to Germany. Zipping is also used in e.g. in The Netherlands and Belgium. It's been required by law in Belgium since 2014 and has been campaigned in The Netherlands since 1989 (apparently).
Also, having lived in Germany for five years and having been in 'Stau' for many times, Germans are also not terribly good/efficient at it. Typical problems: people switch to the lane that is supposed to zip when traffic is going faster, which is obviously counterproductive; and not leaving openings for people to zip.
It's probably still better, but it would be far more effective if all drivers would actually cooperate.
Stau is a bad example for most cases, but yes you will always get some who think they know better, even if they had to learn in the driving school that lane jumping makes it just slower for everyone.
In my experience, zipping as described here - when getting onto the highway - isn't done properly in NL. People still try and force themselves onto the highway or other lane as soon as possible. My colleague called it "eerste blokjesangst".
Just keep going for a bit further, use the whole road, and make sure you're matching speed with the rest of traffic, instead of making them (unknowingly) slow down to let you in. Also keep in mind you ARE allowed to overtake slower traffic on the on-ramp, so if there's a truck there, just pass it on the right, then merge.
Not sure about that. Trucks generally have very powerful brakes and can stop faster than you'd expect. Crashing into the back of a truck can be catastrophic.
Truck do have big powerful brakes, (newer ones with disk-brakes are really awesome) but it still takes a LONG time/distance to slow/stop 80,000lbs from 100km/h.
Kinetic energy is a real bitch.
There are videos of new volvos with 'automatic emergency braking' that is impressive to watch; but that isn't real-world.
In the real world during a 'panic stop' the trailer brakes lock up and the trailer starts bouncing. If you are lucky the tractor wheels don't lock up, but while you have slammed on the brakes, you are still steering and trying to avoid hitting anyone.
316ft for a car vs 524ft for a truck.[1] Almost twice the distance.
And that does NOT match my real-world experience.
I'd say on average it takes 3x-4x the distance to stop a rig.
All the brakes can do is stop the wheels; you still have way more mass generally and momentum to actually get stopped.
While crashing can be catastrophic, I'd like to see some numbers on how many crashes into the backs of trucks were because the truck out-brake'd the smaller vehicle behind it as opposed to the smaller vehicle not paying attention.
The vehicles in the lane beside the truck do not have good visibility in the area in front of the truck. If a vehicle were overtaking the truck intending to immediately go to the lane with the truck, they'll not see the vehicle merging into the motorway from the other side. Thus the theory advises one that merging behind the truck is preferable.
Yep, can confirm - and it really irritates my Dutch wife.
One issue though is the same thing people have mentioned happens in the UK. Sometimes people just try really hard to stop you merging (large trucks seem especially guilty - maybe because many of them have driven from somewhere outside the NL). Most of the time I drive to the end and muscle in anyway, I think of it as expressing my newly approved "Dutch directness". :D
As self driving cars become more common I'm curious if we will see an opportunity to shift to more globally efficient cooperative behavior, or if the need to interop with human-driven cars means the same incentives and behavior patterns will persist.
I’ve heard of the zipper merge in the US too, many cities and states recommend it. I much prefer the zipper merge and I’ve always done it before I knew the name. Some states are even putting up signs about it.
I think the problem with adoption has less to do with the theory of zipper merging working than local culture and traffic enforcement.
I live in Ontario, Canada, and despite of our reputation for politeness, we have some of the worst/most selfish drivers anywhere. Part of this is because there doesn't appear (anecdotally) to be a lot of traffic enforcement, so people now push the limits as much as possible, whether it be texting while driving, running red lights, tailgating or merging improperly.
The only way I could see this work where I live is if there's strict enforcement to ensure it happens, otherwise you'll see behaviours like people not letting in mergers, or a second car trying to squeeze in after the legit merger.
This has seemed so obvious to me forever, but I remember two instances very clearly that illustrate how much people generally hate it in the US.
Once, (in Pennsylvania) there was construction coming up, with maybe still half a mile until the actual cones to merge. This one guy in a massive truck didn't like that people were using both lanes so he straddles his truck across both lanes causing no one to be able to pass on either side.
Second, (in Colorado) there were signs that construction was coming up in a few miles, and the right lane would be closed. So, I was riding in the right lane, passing a massive line of cars in the left lane, getting flipped off the whole time, only to find out there was no closed lane. The signs just hadn't been taken down yet. So I was being flipped the bird because I was using a lane that was fully open.
I think people just don't like feeling that other people are "getting ahead of them", in life in general, and especially in traffic.
Where I live, all too often there just isn't any runway to do this. When you're trying to merge, say, here: https://binged.it/2DTnemt then all you can really do is rip right into traffic and people will just have to make space. It's the worst possible layout for supporting a smooth traffic flow, and it baffles me that they don't lay the extra 200ft of asphalt to improve this, especially in a state that has a DOT that does know how to apply innovative solutions to increase traffic flow like SPUIs and CFIs.
Where I live there is a very strong culture of politeness and kindness in driving. For instance, I often see (and do it myself) that someone has let a person in who is trying to pull out of a hard-to-leave business driveway, with no hope of reward, just out of a sense that other people have helped you out in the past so now it is your turn.
In a recent construction on my way to work they put in two lanes where there was one, which must merge within a hundred yards to get over a narrow bridge. Filling both lanes and zipping would increase the capacity at that location, no doubt. But few drivers do it. Are others worried, as I am, that it would be part of a change in the overall driving culture, normalizing cutting ahead?
That is, could zipping be a local optimization that leads to a global suboptimization, an overall decrease in how reasonable it is to drive around here?
Wow where is this place where drivers are courteous? It is the polar opposite in the UK, many drivers are selfish, aggressive and ignorant, especially around London & South East.
Interesting, cause living in the South East I mostly find drivers that are quite polite on the roads (giving way, respecting crossings, stopping traffic to allow you to merge into the main road, etc).
I suppose it's a matter of expectations. Originally from Portugal so I'm used to seeing far worse people driving on the road.
That's not my feeling, I live in SE London and it's not that bad. There's just a lot of traffic, which makes it difficult and people can be pushy, but when I'm coming off a side road into a queue of traffic I'm usually let in OK and see the same courtesy given to others.
Conversely my mother lives near Worcester, and up there some of the drivers are insane. Nipping the wrong way round a roundabout, dashing across junctions on red. It's like they don't understand the concept of other traffic or sometimes even have actual control over the vehicle. Not everyone obviously, but enough to make my hair stand on end more than just once or twice.
Well said. UK drivers also pathologically avoid the outside/slow lane, exclusively use the middle or fast lane, and police don't fine people who do this. This leads to very miserable motorway driving and unnecessary queues.
" I often see (and do it myself) that someone has let a person in who is trying to pull out of a hard-to-leave business driveway, with no hope of reward"
You're not supposed to do that here (UK) except if you're already in slow moving traffic. You will fail your driving test for doing it. Not only that, but it's overall inefficient and causes traffic jams to form behind you if you slow down.
Like with people who hate zipper merging, sometimes what seems 'polite' isn't what's best for traffic.
I've had a car written off and had a very minor pedal bike crash due to people "being polite" and gesturing people out of side-roads when not safe to do so.
I sometimes do sort-of-the-opposite which is, if I spot someone trying to join the road, and there's plenty of room ahead and behind me, I'll speed up ever-so-slightly to give them more chance of getting on. It's not often, and it's nuanced, but I like to think it's an efficiency positive!
Same here (Scotland). I think the tendency to queue and not fill both lanes is out of a misplaced sense of fairness - you can't help but feel very judged if you run right up an empty right-hand lane all the way to a merge point. Because you really are queue jumping, even if it's the collective fault of all the drivers who created the queue in the first place.
It needs public education to get people over this suboptimal behaviour.
On a tangential note, what's up with everyone everywhere saying "my God, drivers in [where I am] are the absolute worst"? They can't all be right.
I think people just adjust the scale to what they actually see. Deveoping countries with a new car culture are probably objectively worse, but not many people go there and see what it’s like.
Norms change slowly and queueing is a strong social norm. But if it's actually tought in driving schools or even made into law then we can usually overcome it.
This is like how it's pretty natural to let people out of a lift or a train before you enter, regardless of who waited longest. It's just not efficient to get people in before others go out. So we are tought to let people out first.
> what's up with everyone everywhere saying "my God, drivers in [where I am] are the absolute worst"?
I think most of those people have not lived many places. My perception is that there are solid differences in driving culture between some cities. I found San Francisco traffic heavy, but with fairly courteous drivers. Vancouver same. Toronto was atrocious - lived there for ten years and never got used to the aggression and almost sociopathic attitude toward other drivers. Now I'm in Edmonton, where it's back to mostly OK - drivers here are a little more timid than other places but don't lean on their horn for every perceived slight or compromise the whole system to gain a 5 second advantage.
My completely unscientific take is that the most aggravating traffic comes when traffic gets dense enough to be a real irritant (I dunno - say maybe doubling a normal drive time between two destinations), but is still civil enough that most (say 90%) drivers are pretty polite and cooperative. That means that aggressive driving actually pays off, which makes it harder to take for people who don't zip past traffic in the turning lane only to forcefully merge back in.
yeah.. we have merge in turn here, the curved arrow on the road at the end of a lane means this. we also have text signs for "use both lanes" and "merge in turn"
but mostly people are not too keen to actually follow the rules.. i used to follow the pack, now i just follow the instructions and merge as late as possible. - probably this makes me an asshole
>Where I live there is a very strong culture of politeness and kindness in driving.
What happened in America? Has anyone studied the cultural driving differences and why they may be that way? I'm really interested in american road rage and the who/what/where/when/why if anyone has any good resources, I'd love to look at them.
I see the same throughout the US: everyone knows to alternate when a merge is required - and will even call this ‘zippering’ - but does not consistently (or often) do the throughput-maximizing practice of forcing this, by waiting until a merge is absolutely required.
Rather, people often try to avoid the ‘phase transition’ to a forced-merge flow-state for as long as possible, by ad-hoc merging earlier.
Partially that’s because the initial transition-to-zippering can be chaotic. Once established, zippering is easy to follow and well-respected. But, being the “first” to assert an alternating-right-to-merge depends on more judgement & recognition from a specific other driver.
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[ 3.3 ms ] story [ 207 ms ] threadhttps://www.amazon.com/dp/0307277194
https://www.nytimes.com/2016/06/13/world/europe/a-london-sub...
Maybe it's cultural or depends on how eager to walk people are as to utilization factors.
https://sfist.com/2017/01/16/bart_says_actually_standing_on_...
Doesn't this depend on the walking/standing density ratio and walking speed/escalator speed ratio?
Let say the walking density is 1/2 of the standing density. If the walkers walk at the speed of the escalator (i.e. their speed relative to the ground is 2x the speed of the escalator), then the throughput is the same.
Optimal Tip-to-Tip Efficiency is well studied mathematically. Here's the authoritative paper: https://www.scribd.com/doc/228831637/Optimal-Tip-to-Tip-Effi...
There are other issues than eagerness to walk, like physical disabilities and collision avoidance. Ultimately two-speed traffic only works better if you're far from congestion, I believe.
I don't understand what is being further proposed? Making it illegal to merge early?
A similar event comes to mind when you come across someone sitting in the left lane going under the speed limit but completely unaware or bother for the people passing them.
So I guess my point is, while these are great in theory, they don't really work in practice without buy in from the herd (I use herd as this problem can be framed in a similar light as vaccinations and herd immunity).
In the US, when you get to the end of the merge region, most people in the continuation lane will blast by at full speed, leaving no room to get over. I have to sit at the end of my lane, stopped, until I see a gap, and then floor it. That's worse for safety, fuel efficiency, wear and tear on my drivetrain, my own transportation time, and overall road throughput (everyone blocked behind me).
This is a "boil the oceans" type solution. All you have to do is convince everyone to do it.
Here, we can't even get people to stop blocking the box. The SPD is making short YouTube videos with "PRO TIPS" like "Bus lanes are for buses" [1] and "Don't stop in the street" [2]. The average driver is not at the point of thinking about higher level strategy like merge location yet.
[1]: https://www.youtube.com/watch?v=s_62iDA5Z-s [2]: https://www.youtube.com/watch?v=S3dUj6-Kx5k
I'm not talking about merging onto a freeway from an on-ramp. (I'm told the relevant law for on-ramp merging right-of-way varies by state, in the US.)
> The only time other vehicles should have to change their speed is in heavy traffic, when a gap might not exist.
Heavy traffic is the only time a zipper merge might be relevant in the first place, no? In light traffic, just get in the correct lane whenever you want. It doesn't affect anyone else no matter where you do it.
In fast heavy traffic (when drivers aren't leaving the requisite 4 seconds between cars), there's no reasonable gaps into which to merge. Signaling my intention doesn't change anyone else's behavior, and I don't have the guts to sneak my car into a 20' gap at 60mph. Even if I make it, if the driver in front taps the brakes even slightly, we're all going to have a real bad day.
This is a perfect example of how you can't just transplant one aspect of German driving, in isolation, to American highways. On the Autobahn, nobody's driving full speed for an extended length of time at only 1-1.5 car lengths behind the car in front of them. It's reasonable to say "just merge into the gap" because they leave a gap to merge into.
http://mynorthwest.com/474290/washington-traffic-law-reminde...
I certainly see it sometimes. I also see people preventing it sometimes by straddling both lanes.
Actually lane straddling doesn't even work to prevent someone from using the zipper rule. It prevents people from passing other people on the right (nobody should be passing anyone on the right most of the time anyway). But it doesn't prevent someone from merging into the other lane when the time comes. As long as you're pacing yourself vs. the speed of the traffic in the lane you want to merge into, everything's fine. Using the zipper rule doesn't mean you race ahead of everyone before merging, if anything it means waiting a little bit longer and maybe even merging behind a car you would otherwise be tempted to merge in front of.
When traffic is at its peak, it approaches its ideal state: the on-ramp is fully occupied with cars (no space wasted), and everyone's driving at basically the same constant speed up to the merge point, where everyone neatly and cleanly merges, alternating lanes. But if traffic is not at its peak, zippering doesn't require you to race ahead to merge point.
It wouldn't hurt anyone if you did that, of course. Same for everyone else waiting to merge. But there really are lots of people (where I drive at least) who are already on the road/freeway/whatever, who will move onto the (about to end) merging lane, race up to the end of it and force themselves back on the road, a few cars ahead. I've seen so many bad traffic jams made so much worse by people doing this. It makes a bad situation so much worse for everyone. Those are the people the straddlers are guarding against, not the well-mannered zipperers trying to do the right thing.
> But there really are lots of people (where I drive at least) who are already on the road/freeway/whatever, who will move onto the (about to end) merging lane, race up to the end of it and force themselves back on the road, a few cars ahead. … It makes a bad situation so much worse for everyone. Those are the people the straddlers are guarding against, not the well-mannered zipperers trying to do the right thing.
This is basically incorrect. Regardless of how you and straddlers feel about this, using up that empty merge lane on the right is more efficient than straddling or other forms of early merging. That's my understanding, anyway.
Pushing congestion backwards is exactly the cause of a lit of traffic jams. I've observed this myself every single GD day on the 210W freeway between Hill exit and the 134 exchange. People get over way early, causing huge congestion to the merge entrances. If they'd stay left and zipper, everyone in the jam would save about 5-10 minutes. This is thousands and thousands of dollars a day of cost in completely avoidable congestion in just one two mile stretch of highway ( albeit it a particularly egregious one)
In the ideal scenario of zipper merging there is no free right hand lane to shoot ahead in: it is completely filled with people that are alternately taking turns with the other lane to enter the merged lane. The queue is half the length in this case then the prior case. The lane straddler doesn't feel taken advantage of since everyone is entering the queue in the first available location (left or right).
Lane straddlers perform an illegal maneuver (I assume intentional driving in two lanes is illegal in most countries) to pre-empt the more efficient usage of the road. Their righteousness is unjustified: the person that would otherwise pass them in going to the front of the lane would be increasing the utility of the road. They would be more considerate by entering the lane they are blocking and going to the front themselves.
The ruling was also applied inside the OLG Köln: 24.10.2005 - 16 U 24/05) but there are other courts that ruled like that.
(The same ruling applies to "Bundesstraßen")
I’ve been wanting a dashcam. Maybe it’s time to get one.
The problem with the Rettungsgasse is that you only need one idiot to screw it up, but you often get many.
When I enter a traffic jam, I see most cars building it properly, but then I see one or two cars ignoring all others. I can understand that people might forget about it right when they arrive at the traffic jam, but once everybody arounds you do it, some just don't seem to get what's going on.
In other countries, like Austria, the Rettungsgasse is formed on the rightmost lanes, while in Germany, its on the left most lanes. Disparity of rules across EU countries doesn't help here either.
Also, for some reason, once the first police car goes through the Rettungsgasse, I often see many cars that just stop building it. Like "good job everybody, the police went through, we don't need the Rettungsgasse anymore!" even though there is still a jam. The ambulance comes 1-2 minutes later, and it has to fight its way through because of all these idiots.
In Germany the problem with the idiots is particularly bad, because while there are a lot of German idiots on the road, you also get a lot of international traffic with their international idiots on the Autobahn. If you learned to drive in a different country, chances are that you haven't even heard about this, and learning about all the different traffic rules of all the countries you drive through is a PITA.
To reduce this concept to four succinct words:
In the outer tri-state area, and among tourists, this can, and does boil over into real animosity in the surrounding smaller towns and suburbs, where heavy police activity usually muscles up against aggressive city driving tactics, to keep the peace, and establish normitive boundaries to clue the unititiated in on the fact that they’s outside city limits, and it doesn’t fly in other counties.But to elaborate, city merging means maintaining sub-six-inch proximity to adjacent vehicles in slow moving traffic. This is done to acheive a number of effects, from preventing pedestrian induced gridlock/deadlock at crosswalks, to nosing in on corners, such that a wedge forces surounding vehicles apart, by way of slow-motion chicken. It requires an extremely accurate sense of vehicle volume and the bounding box definition of your car’s footprint/shadow in the lane.
This manner of merging also plays into the fact that most professional drivers, from taxi cabs to box trucks, will yield, because they kind of get paid by the hour.
The only wrinkles to this driving style are Wall Street Lambos, McLarens and such, and the occasional motocycle. More often than not, these exceptions will often appear within proximity before you register their presence, and typically outmaneuver you, before you have a chance to assert position, even if you do see them coming.
It only leads to the perception of "cutting" when more idiots merge well before the natural merge point then logically where the lanes pinch back down.
Just like the ramp meters that limit cars entering the freeway. But instead a dual light that encourages zipper merging via offsetting green signals for each lane.
In a more general sense on a highway any time a car comes to a full stop you have the chance to create a phantom traffic jam as the stop travels back along the incoming stream of cars.
https://static1.squarespace.com/static/5005afd7e4b0a6953320b...
As an English driver: <extreme tutting> get to the back of the queue like everyone else!
As a Cambodian driver: we are all stuck in a sea of motos, and being on time for anything is unimportant. Of course you may merge into my lane.
What that means is if someone tries to push their way in, I will block them off.
If someone is stuck and trying to get out of a side road / park, I will always let them in.
Obviously people should zipper off before the light to load both lanes evenly and get as many people through the light before it cycles. Then after the light everyone should go forward and re-merge back into a single lane again.
Yet people will stubbornly pile into the left lane before the light leaving the right mostly empty then play games blocking people from merging in after the light.
Well, that's when they actually move through the light in a timely manner if not distracted from texting while stopped at the light :/
There is a long lane, often backup up past a stop light and then it goes to 2 lanes for about 50 yards before the light that lets you turn left onto the interstate.
Nobody ever turns from the rightmost lane, everyone stays in the left lane. When I use the right lane and pass people I get angry reactions, people trying to block me from merging back in, and a couple times people cursing at me and following my car.
Luckily I'm a big guy who's not easily scared.
I've stopped caring about other people's sense of fairness in these situations, and I always use the empty lane and merge late. The law is on my side, and people can glare and honk as much as they like. I just saved five-ten minutes of not queuing, they could too if they all learned to drive correctly.
All it would take would be a consistent change of sign showing merging in turn at lane-merge to change this behaviour
The odd thing is that you do see very occasional zip-merge signs in the UK, which tend to reinforce the idea that zip-merge should any be used in exceptional circumstance.
People here will follow each other incredibly closely, even at high speeds, and quite often they won't slow down to let you in if you're trying to merge.
What most Americans have a hard time understanding is that German driving school, or Fahrschule, requires the student to master these "advanced" techniques. Unlike in the USA where if you can operate the throttle and the brakes you're good to go.
Not sure where all that anger comes from but I am happy that a hardly ever saw it in other countries where I drive or take a taxi.
It all seems very theorical and not that useful.
And I see this working every day since where I live the rule applies. Of course there will always be the occasional smart guy who rides in the ass of the car in front in order to not let anyone pass and save 1-2 seconds at the price of causing everyone behind him 10 times the delay. This forces the cars trying to merge to come to a full stop, then forces some of the cars on the other lane to fully stop in order for the merging cars to be able to accelerate and merge.
Also, having lived in Germany for five years and having been in 'Stau' for many times, Germans are also not terribly good/efficient at it. Typical problems: people switch to the lane that is supposed to zip when traffic is going faster, which is obviously counterproductive; and not leaving openings for people to zip.
It's probably still better, but it would be far more effective if all drivers would actually cooperate.
Just keep going for a bit further, use the whole road, and make sure you're matching speed with the rest of traffic, instead of making them (unknowingly) slow down to let you in. Also keep in mind you ARE allowed to overtake slower traffic on the on-ramp, so if there's a truck there, just pass it on the right, then merge.
Truck do have big powerful brakes, (newer ones with disk-brakes are really awesome) but it still takes a LONG time/distance to slow/stop 80,000lbs from 100km/h. Kinetic energy is a real bitch.
There are videos of new volvos with 'automatic emergency braking' that is impressive to watch; but that isn't real-world.
In the real world during a 'panic stop' the trailer brakes lock up and the trailer starts bouncing. If you are lucky the tractor wheels don't lock up, but while you have slammed on the brakes, you are still steering and trying to avoid hitting anyone.
316ft for a car vs 524ft for a truck.[1] Almost twice the distance.
And that does NOT match my real-world experience. I'd say on average it takes 3x-4x the distance to stop a rig.
[1]https://www.hg.org/legal-articles/stopping-distances-for-com...
While crashing can be catastrophic, I'd like to see some numbers on how many crashes into the backs of trucks were because the truck out-brake'd the smaller vehicle behind it as opposed to the smaller vehicle not paying attention.
One issue though is the same thing people have mentioned happens in the UK. Sometimes people just try really hard to stop you merging (large trucks seem especially guilty - maybe because many of them have driven from somewhere outside the NL). Most of the time I drive to the end and muscle in anyway, I think of it as expressing my newly approved "Dutch directness". :D
That's the issue with most of solutions to traffic though.
Minnesota[1]. Other states[2]. My home town[3].
[1]https://www.dot.state.mn.us/zippermerge/
[2]https://www.fleetowner.com/driver-management-resource-center...
[3]https://www.ajc.com/news/local/gridlock-guy-transportation-o...
I live in Ontario, Canada, and despite of our reputation for politeness, we have some of the worst/most selfish drivers anywhere. Part of this is because there doesn't appear (anecdotally) to be a lot of traffic enforcement, so people now push the limits as much as possible, whether it be texting while driving, running red lights, tailgating or merging improperly.
The only way I could see this work where I live is if there's strict enforcement to ensure it happens, otherwise you'll see behaviours like people not letting in mergers, or a second car trying to squeeze in after the legit merger.
Once, (in Pennsylvania) there was construction coming up, with maybe still half a mile until the actual cones to merge. This one guy in a massive truck didn't like that people were using both lanes so he straddles his truck across both lanes causing no one to be able to pass on either side.
Second, (in Colorado) there were signs that construction was coming up in a few miles, and the right lane would be closed. So, I was riding in the right lane, passing a massive line of cars in the left lane, getting flipped off the whole time, only to find out there was no closed lane. The signs just hadn't been taken down yet. So I was being flipped the bird because I was using a lane that was fully open.
I think people just don't like feeling that other people are "getting ahead of them", in life in general, and especially in traffic.
In a recent construction on my way to work they put in two lanes where there was one, which must merge within a hundred yards to get over a narrow bridge. Filling both lanes and zipping would increase the capacity at that location, no doubt. But few drivers do it. Are others worried, as I am, that it would be part of a change in the overall driving culture, normalizing cutting ahead?
That is, could zipping be a local optimization that leads to a global suboptimization, an overall decrease in how reasonable it is to drive around here?
I suppose it's a matter of expectations. Originally from Portugal so I'm used to seeing far worse people driving on the road.
Conversely my mother lives near Worcester, and up there some of the drivers are insane. Nipping the wrong way round a roundabout, dashing across junctions on red. It's like they don't understand the concept of other traffic or sometimes even have actual control over the vehicle. Not everyone obviously, but enough to make my hair stand on end more than just once or twice.
You're not supposed to do that here (UK) except if you're already in slow moving traffic. You will fail your driving test for doing it. Not only that, but it's overall inefficient and causes traffic jams to form behind you if you slow down.
Like with people who hate zipper merging, sometimes what seems 'polite' isn't what's best for traffic.
I've had a car written off and had a very minor pedal bike crash due to people "being polite" and gesturing people out of side-roads when not safe to do so.
It needs public education to get people over this suboptimal behaviour.
On a tangential note, what's up with everyone everywhere saying "my God, drivers in [where I am] are the absolute worst"? They can't all be right.
I think people just adjust the scale to what they actually see. Deveoping countries with a new car culture are probably objectively worse, but not many people go there and see what it’s like.
This is like how it's pretty natural to let people out of a lift or a train before you enter, regardless of who waited longest. It's just not efficient to get people in before others go out. So we are tought to let people out first.
I think most of those people have not lived many places. My perception is that there are solid differences in driving culture between some cities. I found San Francisco traffic heavy, but with fairly courteous drivers. Vancouver same. Toronto was atrocious - lived there for ten years and never got used to the aggression and almost sociopathic attitude toward other drivers. Now I'm in Edmonton, where it's back to mostly OK - drivers here are a little more timid than other places but don't lean on their horn for every perceived slight or compromise the whole system to gain a 5 second advantage.
My completely unscientific take is that the most aggravating traffic comes when traffic gets dense enough to be a real irritant (I dunno - say maybe doubling a normal drive time between two destinations), but is still civil enough that most (say 90%) drivers are pretty polite and cooperative. That means that aggressive driving actually pays off, which makes it harder to take for people who don't zip past traffic in the turning lane only to forcefully merge back in.
but mostly people are not too keen to actually follow the rules.. i used to follow the pack, now i just follow the instructions and merge as late as possible. - probably this makes me an asshole
What happened in America? Has anyone studied the cultural driving differences and why they may be that way? I'm really interested in american road rage and the who/what/where/when/why if anyone has any good resources, I'd love to look at them.
Rather, people often try to avoid the ‘phase transition’ to a forced-merge flow-state for as long as possible, by ad-hoc merging earlier.
Partially that’s because the initial transition-to-zippering can be chaotic. Once established, zippering is easy to follow and well-respected. But, being the “first” to assert an alternating-right-to-merge depends on more judgement & recognition from a specific other driver.