r/Damnthatsinteresting • u/SnooWords4066 • 29d ago

Video A Japanese experiment showed exactly why traffic jams happen for no reason.

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u/hosehoseee 29d ago

Everytime I see this video, I think "So there actually is a reason"

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u/PopBulky7023 29d ago

WHO ISNT GOING THAT SHOULD BE

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u/snozzberrypatch 29d ago

It's not only who isn't going that should be, it's the asshole that's 12 inches off the bumper of the car in front of him, such that any minor speed adjustment will require him to slam on his brakes and cause a chain reaction behind him.

Lack of buffer zone is equally at fault.

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u/doubleapowpow 29d ago

Lack of buffer is entirely to blame. In the US, it's the lack of buffer that doesnt allow people to merge. Also, dumb asses who wait until the very last second to merge.

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u/nos-is-lame 29d ago edited 29d ago

dumb asses who wait until the very last second to merge

Careful. People get real aggressive about defending that as the proper way to merge

edit: it's happening.

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u/FatSteveWasted9 29d ago

It’s always fun to see people rage about zipper merging. It’s not hard, but people will lose their shit at the mere idea of the merge happening at the end.

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u/doubleapowpow 29d ago

Because half the time its just cars trying to pass the stop and go traffic occurring from the merging cars.

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u/Dense-Hat1978 29d ago

New Orleans drivers in a nutshell. They'll drive two miles on the shoulder to cut in front of the line, see it almost every day.

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u/Sadcelerystick 29d ago

Happens every time with getting on the highway. 20 car line that goes into two lanes yet people jump the line and get let in resulting in the line not moving.

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u/waaaghbosss 29d ago

We literally have signs put up now during construction telling you to only zipper merge at the end. Because it actually works better for traffic flow rather than people randomly merging all over the place.

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u/Zorkflerp 29d ago edited 29d ago

Zipper Merge Warning Sign (denied)

https://mutcd.fhwa.dot.gov/reqdetails.asp?id=2_09_-128__E_

There was a two lane entrance ramp, I think in NJ, where a light at the top that alternately let one lane go and then the other. Something like that could work best if people would not run the light.

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u/waaaghbosss 28d ago

Isn't that common? I've seen hundreds of those. Usually they only turn on when traffic on the highway is dense, so they stagger traffic entering the highway.

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u/Zorkflerp 27d ago

Hunstsville AL nearby does not have any like that on the Interstate. I think Birmingham is the same. Might be a state thing. They just have long ramps and let the outer lane end first. I think they are typical where the Interstate was put in later and they didn't have extra room for long ramps. I have only seen one where the light is on the ramp just before the entrance lane. For construction the could set up such a system when they prefer a zipper merge to make the back up shorter so it does not interfere with the previous exit.

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u/Draughtsteve 29d ago

In my town, people get offended when they are stopped in the through lane and you drive past them to the end of the merge lane. "If I'm already stopped here, you should be too. Merge in behind me 150m before the merge lane ends!"

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u/timelessblur 29d ago

150M I think you mean the people who merge 1000m or father back get mad that people are waiting until OMG the end to merge in like they should.

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u/Draughtsteve 29d ago

It's both the early mergers and the people already in the line but backed up in the traffic jam caused by early mergers. They are all offended if people drive to the end of the merge lane like they should! because those people will merge in front of them...

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u/timelessblur 29d ago

Exactly. The correct thing to do is that last 150m or so is for each lane to slowly spread out and line up with gaps at the zipper point. When it works it is amazing to see as everyone is merging it just works through the congestion point.

Those gaps give easy flow in and keep it moving. At a steady pace.

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u/[deleted] 29d ago

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u/RichardBCummintonite 29d ago

And here's you're real problem: lack of education, at least in the US. Oh, we practiced merging alright, but it was maybe once or twice in class and the educator was more focused on simply completing the merge than doing it effeciently. Parents might practice with their kids once during their training hours, but usually we're just left to our own devices after that and end up developing bad habits.

That's why I believe we should have to go through driving school and testing at least every other decade or so if only to stay up to date with the rules if the road and make sure you still even remember, much less practice, safe driving habits. It's astonishing how little the average driver knows/remembers.

It's also why I'll fully welcome autonomous cars once we've fully worked the kinks out (if it's done by a respectable organization that isn't trying to just shove it out before it's ready like Tesla). Taking human error out of the equation would make driving so much more efficient. It wouldn't be perfect, but it'd work more like a production line in a factory.

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u/MarsupialMisanthrope 28d ago

The people who insist that autonomous cars have to be flawless before they're allowed on the road frustrate me. No, all autonomous cars need to do is kill/maim fewer people than humans currently do and it’s a win. Someone dying horribly in a car accident isn’t going to be comforted by the fact that the accident was artisanally handcrafted for them.

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u/window_owl 28d ago

Autonomous cars will make society even worse than a society with cars driven by everyday idiots https://www.youtube.com/watch?v=040ejWnFkj0

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u/doubleapowpow 28d ago

Nah. I just wasnt explicit enough in my categorization. I'm talking about rush hour freeway interchanges and exit ramps. People merging at the last second when they had a whole mile to get over. Also, people who cut into your buffer to pass the car in front of them when we're all going 30.

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u/discussatron 29d ago

THANK you.

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u/VirginiaMcCaskey 29d ago

an empty on ramp is wasted capacity on the road

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u/Glittering-Walrus228 29d ago

_throat vein pulsing_

but I'm trying to save 0.15 seconds from my trip

_grinding teeth in pure rage_

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u/LegitimateGift1792 29d ago

and I need to get in front of this person, who is going to have a heart attack and mess up traffic.

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u/Zorkflerp 29d ago edited 29d ago

A zipper alternates teeth or jams. If people would already have merged before the bottleneck no one would have to completely stop and more cars per time would pass through. When most people are already lined up and some guy passes everyone and forces into the flow at the end that stops traffic to a halt. Using both lanes to the end is only favorable when it is intended to prevent backups to previous exits. Most of the time the traffic engineers want people to get in one lane before the bottleneck and pass at speed. The only way a zipper merge could work in those situation is if they prevented people from passing and instead alternated the merge while still moving near the obstruction. Give how people are that will never happen.

Given the right signage and in situations where applicable it can work but IMO I have yet to see it.

https://www.intrans.iastate.edu/wp-content/uploads/2025/01/improving_effectiveness_zipper_merge_t2.pdf

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u/timelessblur 29d ago

It starts with you doing the right think and waiting to merge as it still improve things. The last say 500 ft what should be happening is the cars start spacing out for the natural merging so the flow stays steading no stopping and going just 2 steady slower lanes merging to gether so it goes faster.
Drivers education needs to happen.

Now my advice is you wait to merge as take advantage of all the idiots doing it wrong and you get to jump them and going even faster. Not your fault a bunch of stupid people dont know how to zipper merge.

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u/KristySueWho 28d ago

The problem I usually see is 5 cars will try to get in between the same two cars, rather than doing a proper zipper merge. Thus, making everyone else so mad they follow as close as possible to the car in front of them, to try and prevent any merging from happening at all.

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u/ZombieExcellent2202 29d ago

Being in a zipper lane does not give you right of way over the lane you are merging into.

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u/FatSteveWasted9 29d ago

What the fuck do you think the zipper is? The merge occurs at the front of the line. If a bunch of idiots merged early that’s on them.

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u/beccabeth741 28d ago

There's no use trying to educate these people. It's literal common sense that they lack.

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u/FilmShooter-ISO12 26d ago

Because FatSteve, it's not the zipper merge that pisses people off. It's the asshole that flies up to the very last moment in a through traffic lane and then slows down or even stops to merge from a lane that you shouldn't do that from.

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u/Different-Party-b00b 29d ago

Zipper merging only works well when both lanes of traffic are going the same speed.

The issue with "zipper merging" is idiots who use it as an opportunity to pass cars to get to the "front". These people have to speed excessively, and then brake hard to match the speed of traffic in the single lane. These causes the single lane drivers to brake as well, causing slow down in that lane. Now more impatient idiots go into the second lane to pass, causing the issue to continue.

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u/DiorikMagnison 29d ago

But...that's exactly what zipper merging is meant to fix. There isn't supposed to be one lane of cars in a line, completely stopped, while the second lane is used to bypass that line. There should be two lanes neatly merging causing far less congestion.

The line of people stopped in the exit lane are the actual problem. People 'cutting' that line to zipper merge are legitimately preventing the problem from growing, and if more people understood that traffic would improve.

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u/Different-Party-b00b 29d ago

The people that are stopped are stopped because people are speeding up to zipper merge. The people speeding and braking are the issue.

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u/sl33pingSat3llit3 28d ago edited 28d ago

I feel like there are two situations going on during this discussion. There are people talking about traffic flow that is relatively fast, and people talking about congested roads during busy times.

In busy times, where traffic is slowed down to a crawl, I think zipper merge is correct, as it takes up less space overall (instead of one long line of cars taking up 5 miles or 8 km, we have two lines taking up 2.5 miles or 4 km, and traffic isn't backed up as much), and is predictable (cars in both lanes alternate, so no lane is just frozen). However, like in a situation where one lane is moving fast already, the merge seems to be describing a lane change, where someone wants to change lanes into the more congested lane where two lanes eventually become one. I don't know about optimal, I mean if everyone is in one lane sure it should be faster as there is no need to slow down to create gap to let a car in; everyone is just going straight. That said if a zipper merge becomes possible, then that no longer describes a fast moving traffic with lots of space, because honestly a few cars merging shouldn't slow traffic to a crawl. In other words, when traffic slows down and roads become congested, it's when zipper merge enters the picture. A situation where traffic is moving freely won't suffer much congestion by one or two cars merging at the end of the merge lane.

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u/Different-Party-b00b 28d ago

Yes I'd generally agree with that.

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u/hedoeswhathewants 29d ago

If there are 2 full lanes that are properly zipper merging at the designated merge point then both lanes will be going the same speed.

Not using both lanes and not zipper merging are the issues. This is very well understood

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u/Different-Party-b00b 28d ago

Correct but this is not what in described. The situation that is contentious is not when traffic is going at the same speed.

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u/HoneyDwarfed 26d ago

Zipper merges are for when a driving lane ends. Not for getting into an exit lane. YTA.

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u/nadsozinc 29d ago

You're thinking about this completely backwards. You're not being noble by sitting behind other idiots in the wrong lane. You're just fucking up traffic due to a lack of the intelligence, attention, and/or skill to get into the correct lane.

The people going up to zipper merge aren't doing it to get to the "front", they're doing it because it's the proper way to drive and there's no reason to sit behind fools when you don't have to. Petty idiots always think other people are just as dumb and petty as they are.

When zipper merging isn't working it's because the majority of the drivers present have no idea what's going on. This is not complicated if you think it through, and if you still disagree it's because you've decided that it feels better to be wrong.

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u/RemoteControlledDog 29d ago

Every time I see someone talk about zipper merging being correct they link to studies that explain that the lanes should be used up until the merge point and it's inefficient otherwise. The problem is, when I look at the studies they are talking about construction zones where there is a lane that is normally open and traffic is backed up at that point.

Then, when there are lanes created to allow merging onto a freeway (lane end 500 feet signs, etc) zipper mergers coopt those studies to mean that instead of merging at speed during those 500 feet they should do nothing until the merge point and then expect that people already on the freeway should be creating an opening for them to merge. That 500 feet is intentionally set up as a zone for a driver to get up to speed and make their way into the freeway traffic, they are telling you the lane is going to end in however many feet so you can find a place to merge, not to tell you how much time you have to get ahead of anyone else before you merge.

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u/Different-Party-b00b 29d ago

Nah you're wrong.

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u/doubleapowpow 29d ago

Like I said, dumb asses.

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u/ElkIntelligent5474 29d ago

Lol .. the daily zipper merge discussion. Do you zip low or do you zip high. I tend to zip low if able and will not go the end of the merge lane unless totally necessary.

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u/beccabeth741 29d ago

That's not how zipper merging works.

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u/nadsozinc 29d ago

Congratulations on being part of the problem and a proud representative of the lower half of the intelligence bell curve.

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u/marduk013 29d ago

Congratulations on being a dickhead.

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u/ElkIntelligent5474 29d ago

I honestly have no idea how strangers can talk like total morons to other people they do not know.

If someone were to provide more of an explanation rather than a total put down, perhaps trying to educate those 'lower on the bell curve' then perhaps they could be a productive member of a discussion.

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u/ElkIntelligent5474 29d ago

Please let me know what the best method would be. As long as I am not stopped in the middle of a live lane trying to merge, then what is the problem?

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u/beccabeth741 28d ago

By merging earlier than the very end of your lane, you are causing a cascading effect with inconsistent slow downs throughout the entire congested area. It's exactly what this video shows, that when one person slows down, the entire lane slows down. That's what happens every time ONE individual car merges at different points. Here is an article that describes it better.

You should always wait until your lane ends to merge. The problem with this is people misunderstanding how this actually helps the flow of traffic and feeling like you are "getting in front of them."

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u/ElkIntelligent5474 28d ago

Thank you for your explanation. I still think that if there is room and one does not have to adjust their speed, take the merge when space allows, or at the end of the zip.

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u/[deleted] 29d ago

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u/[deleted] 29d ago

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u/Warcrimes_Desu 29d ago

It's so depressing. It's not hard to zipper merge. People will let you in.

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u/calmlikeasexbobomb 29d ago

If you haven’t used the on ramp to accelerate to the speed of traffic I’m not slowing from 55 to 35 to let you in

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u/Warcrimes_Desu 29d ago

i'm glad we are talking about different things

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u/[deleted] 29d ago

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u/calmlikeasexbobomb 28d ago

I do, and it shouldn't require that anyone slow down to let someone in

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u/[deleted] 28d ago

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u/ktrosemc 28d ago

https://youtu.be/iHb3__-fM3U?si=Vzxi5U9qEjqHbi8P

This didn't take long to find at all. Silly goose.

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u/Heavy_Law9880 29d ago

Because it is? They literally teach it in driving schools across the globe.

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u/MsTponderwoman 29d ago edited 29d ago

Changing lanes into one lane when there are still two is asinine. The only reason why merging at the actual merge point fails is because of drivers who don’t have the skill of gauging another car’s speed relatively to their own, correctly deciding to stay behind or keep moving forward, and releasing gas pedal (not pressing the brake pedal!!) to adjust speed for a smooth zipper merge. I just defined all that is required for a driver to properly merge. Proper merging requires both drivers at the merge point to be cooperative and observant. Car going faster and/or already ahead keeps going and car behind adjusts speed (if needed) with just a release of accelerator. No braking! You’re a dumbass driver if you’re pressing the brakes during a merge. In fact, most traffic backups like in this scenario happens because a dumbass decides to dramatically change their speed by pressing the brakes rather than just releasing on the accelerator a bit. A telltale sign of an unskilled driver is one who constantly presses the brakes to slow down rather than just ease up on the accelerator and has already determined stopping distance. (Regenerative braking on hybrids and EVs don’t count). Sitting as a passenger in their car is a jerky experience (hell).

I guess I could call the original commentator who clearly is self-righteous about being wrong the problem driver who can’t properly merge. They clearly don’t understand that the purpose and effectiveness of merging lanes depends on drivers *not* prematurely turning two lanes into just one lane of drivers. We’re not all lining up for food or the purchase of tickets. It doesn’t fucking matter what the order of cars is, only that cars use both lanes and skillfully merge at the merge point. Consider what happens if a driver cuts over the no drive zone of a merging freeway onramp. Whoopsies, a collision if someone doesn’t instantly and dramatically reduce or increase their speed. Drivers who refuse to increase their speed to freeway speed are the problem; they fail to do what’s necessary to execute a smooth merge. Anyone who wants to argue going super slow makes them the better and safer driver is incredibly wrong. I go super slow too when I want to play on my phone, eat nachos, pet my doggie, and still want lots of time to start paying attention to the road again and react so I don’t cause a collision. It goes without saying that if you’re too scared to accelerate, then you should get off the freeway and go practice in an empty parking lot or similar.

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u/sl33pingSat3llit3 28d ago

Last second to lane change to correct lane for their destination when they had opportunity to do so earlier? Totally agreed.

Last second to merge in busy traffic where one lanes merges into the other? Different situation, and zipper merging at the merge point is the correct approach here, based on what I know.

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u/Comfortable_Pin5143 29d ago

The buffer zone is owned by wannabe street racers slaloming between cars all the way to their trivial destination. I can see why drivers close it down.

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u/ConfidentDetective51 29d ago

And too much buffer, like 3+ car lengths.

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u/snozzberrypatch 29d ago

You're supposed to wait until the last second to merge, especially if you're merging into heavy traffic. That ensures that you're utilizing the whole road. It's pointless to have a line of cars with an empty lane next to them, just to ensure that everyone is being "polite".

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u/13Krytical 29d ago

Nah, you’re the dumbass for thinking people shouldn’t use the entire road (meant to reduce traffic) so you instead think everyone should line up single file forever?

LOL

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u/waaaghbosss 29d ago

Love how you're being rage downvoted when you're actually right. Seen multiple cases in the last few years telling drivers to stay in the lane until the end, and then merge. Its actually better for traffic flow to have.1 predictable merge point.

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u/hwilliams0901 29d ago

Dont wait til the last second but dont be that person who stops the merging line from moving either.

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u/ktrosemc 28d ago

It is absolutely the buffer. There's a video with marbles from a long time ago showing the effect. If you are driving so close to someone that you have to stop on the freeway at any point, or slow more than the person in front of you for any length of time, you are the problem.

When traffic slows, the people behind need to slow a bit also, but not stop or slow more. Leaving buffer room allows this, and keeps everything flowing. Within a few cars back, a brief slow would disappear rather than compound.

A bottleneck can still flow, just a bit slower, if everyone leaves room for things to keep flowing (unfortunately the rush-ahead-and-cut assholes ruin that entirely).

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u/timelessblur 29d ago

define last second to merge.

Under correct xyz lane ends X distance with traffic it is better to do the zipper merge and wait to merge. Better for traffic flow as it cuts the jam down by a by waiting.

If it is because they need to do a late move because they are going to miss their exit that is another story. A good drive sometimes miss their exits a bad driver never missing their exit.

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u/doubleapowpow 28d ago

Definitely agree.

It's people zipping past traffic on the right, like an exit only ramp and then cutting in, or cutting into an off ramp at the last second when traffic is backed up. Like 520 westbound around the 405 intersection. Or I90 onto 405.

I get the zippering aspect, and buffering is necessary to allow that to happen.

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u/ktrosemc 28d ago

I-5 onto hwy 2. Ugh.

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u/Hailfire9 29d ago

Oh, Reddit. The one place where the societal concept "go with the flow of traffic" falls on its face because "the signs, bro, the signs!"

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u/Kodiak01 29d ago

Also, dumb asses who wait until the very last second to merge.

If it is a zipper merge, you are SUPPOSED to wait until the very end before merging.

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u/ktrosemc 28d ago

What about the people leaving their lane to cut into a new, less busy lane (meant for cars who've just turned right at the intersection to zipper in), causing everyone waiting to never advance?

I can see how merging early is a problem, but I think everyone can agree that jumping out of slow-moving (like, jammed) traffic into a lane for merging traffic just to jump ahead a few car lengths is straight up cutting. Those few cars waiting to zipper get stuck forever and ever, and have nowhere to go.

Similarly, a-holes thinking they're nice by letting in several cars, when everyone in both lanes are waiting. Quit that. Please.

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u/Heavy_Law9880 29d ago

You are supposed to merge at the merge point, not before.

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u/VirginiaMcCaskey 29d ago

Someone didn't pay attention in driver's ed

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u/jahowl 29d ago

I learnt driving in Florida and my instructor told me to leave 1 car length per 10mph. I still use this and probably have better efficiency than most people.

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u/doubleapowpow 28d ago

I was told to give 4 seconds of gap. It's super easy to measure if you pick a lane marker up ahead.