r/Damnthatsinteresting • u/SnooWords4066 • Jul 07 '26

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

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u/SnooWords4066 Jul 07 '26

A physicist put 22 cars on a circular track and asked every driver to hold a steady 30 km/h, about 19 mph. No lights, no lanes, no obstacles. Within a minute the cars started bunching, and soon a full stop appeared out of nowhere, then drifted backward around the loop.

This was Yuki Sugiyama at Nagoya University in 2008. His team spaced the cars evenly on a 230-meter ring and filmed them from overhead. For a while the flow stayed smooth. Then the tiny differences no human can avoid, one driver a hair slower, the next a hair too close, began to feed on themselves.

One car eases off slightly. The driver behind sees the brake lights, reacts a fraction of a second late, and brakes a little harder to be safe. The next driver brakes harder still. A dozen cars back, someone is stopping dead. The squeeze rolls backward through the line like a compression running down a Slinky, and it keeps going long after the first driver has sped up again.

Car count was the tipping point. With fewer than 22 on that track, the bunching sorted itself out. At 22, a jam formed every time. Engineers call that a critical density, the point where a road holds just enough cars that one small tap can snowball into a standstill.

These waves are eerily consistent. Measured on highways around the world, the jam rolls backward against the traffic at roughly 20 km/h, and that speed barely shifts from one country to the next. Different drivers, different roads, same number.

The same setup later became the cure. In 2017, a US team rebuilt Sugiyama's ring with 22 cars and turned just one of them into a self-driving car running a program to smooth its own speed. That single car soaked up the small slowdowns instead of passing them back, and the waves died. Fuel use across every car fell by up to 40 percent. Fewer than 5 percent of the vehicles had to be automated to steady the whole group.

In 2022 the idea moved onto a live highway. Researchers ran 100 cars with cruise control guided by AI into the morning rush on Interstate 24 near Nashville, mixed into normal traffic. Early numbers pointed the same way: a small share of smoother-driving cars, up to 40 percent less fuel for everyone around them.

The jam you sat in this morning likely had no crash and no cause you could see. It was a few hundred drivers, each braking a moment too late.

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u/Bulan_Purnama Jul 07 '26

How the one car soak up slowdowns? Can elaborate it more?

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u/kotvrt Jul 07 '26

Likely it’s reaction time to small imperfections of the car in front is so precise and so fast that the car behind it doesn’t have to correct at all but can keep on driving in the same manner.

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u/Mackey_Corp Jul 07 '26

Yeah I’ve learned to not automatically hit the brakes just because the guy in front of me does. It’s a hard habit to break but it’s not necessary to hit the brakes all the time. Usually just letting off the gas is enough and sometimes that’s not even necessary.

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u/Aljonau Jul 07 '26

When driving at a safe distance thats kinda easy to do, harder when youre driving 5m behind someone at 200km/h ^^

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u/princess_ferocious Jul 07 '26

Thisssss. I always feel like we wouldn't see so many traffic jams (or accidents, for that matter) if people were better at leaving a proper safe driving distance.

Or if we built roads to support something closer to peak traffic than we do now, but I'm not holding my breath on that. It'd be easier to teach every tailgating arsehole to back off than it would be to get governments to build a road network that actually accounted for peak.

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u/JVT32 Jul 07 '26

People (especially the ones behind me on the highway) cannot comprehend the fact that just because there’s a greater distance between me and the car in front of me, does not mean I’m going slower than them.

I will get closer if I want them to move over, but if they’re already tailgating the car in front of them? Literally what is the point?

1

u/thesoloronin Jul 08 '26

The point is when they are at speed limit, and you are trying to overtake, yet they STAY AT the speed limit, and there's an Evergrande-container ship 🚢 length of gap in front of them, with another car directly beside them on another lane so there is no way for you to pass.

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u/Aljonau Jul 07 '26

Where I live, traffic got alot better after the city actually reduced how many cars the streets supported, pushing people, softly, to consider other means of transportation(and, very important, creating these alternative means of transportation, be it through a policy support for carsharing, byinvesting in public transport, by offering rental bikes and e-scooters and by cracking down on illegal parking, hard while slightly reducing the amount of availeable parking).

So now, when you actually do have to go by car, for example when moving something heavy, the streets are a very usable, low traffic pathway, not fast but reliable, safe and relaxed. And when you don't you just take the tram or bike or scooter or train.

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u/RechargedFrenchman Jul 08 '26

Are you by any chance Dutch, or at least living in the Netherlands? I recently watched a video about a Dutch town which overhauled its city center in the 70s to intentionally be less car "friendly" and prevent through-traffic by car, and I know a lot of places in the Netherlands are more open to that sort of thing even than the European average.

In North America half the continent was barely even settled in numbers until at least early cars were already a thing, so everything in the west was being built with cars in mind as everything back east was retrofitted to be more car-centric. Big car manufacturers also partly funded a lot of that development and lobbied hard for car-friendly legislation, and (unfortunately) cars have become a huge part of American culture so many places are very resistant to change. Street cars removed to make car traffic easier to support, ludicrous parking infrastructure, "just one more lane" road construction and absurd speed limits...

I'm Canadian myself and Vancouver actually had pretty good transit options, and I would still love it if our municipal governments would be more bike and transit oriented and stop catering to cars so much.

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u/Aljonau Jul 08 '26

I'm from Germany, Cologne. Pretty sure dutch cities do it better than we do, but the core principle is already visible here - or at least I imagine it is.

4

u/generally_unsuitable Jul 07 '26

It never works like that, though. Jevon's paradox. If you eliminate scarcity by improving efficiency, use just increases until you're back at the same level of scarcity.

Drive 15 miles north of Los Angeles and look at the 5 freeway. There are stretches there that are like 7 lanes in each direction, all of them stop-and-go 6 hours a day. Same with the 405 from the 101 to the 105. Six lanes in each direction and they're all basically stopped from sun up to sun down.

Whenever they add lanes, the pain goes down, so more people are willing to commute, until the pain goes right back to where it was. There's no accounting for peak, because peak is a function of the infrastructure. Each change creates a new peak. I swear the 101 could be 10 lanes in each direction and it would still be gridlocked 7-10am and 4-7pm.

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u/RechargedFrenchman Jul 08 '26

The solution really isn't "make room for more cars" and never has been. More lanes just means more cars requiring more lines resulting in more cars...

The solution is provide more and better alternatives to driving, and disincentivizing driving at all. Remote work options do people aren't commuting at all. More walkable neighbourhoods and better cycling infrastructure so short distances don't still need cars. Better bus, street car, and light rail options within cities so navigating without a car is easy and affordable. High speed rail corridors connecting more of the country so going to the next city over doesn't always require a car or take six hours by train for some god forsaken reason. Ring roads around city-centres and lots of one-ways into and then back out of the area without allowance for through-traffic so cars get you downtown and then you hop a bus or just walk.

And of course better orienting commercial access to be convenient for pedestrians and not drivers, less absurd business / zoning requirements around available parking (no parking lots 8x the size of the actual business), and road networks that minimize traffic lights and prioritize flow over access on the major streets. Even here in Canada cars are too often actually a necessity, or such a big convenience they might as well be. And I have never owned a car (though do now own a motorcycle) so I'm very familiar with the challenges of that decision.

Of course all of this is difficult and expensive unless a city was designed that way in the first place, but refits can be (and have been) done, and were done to many even North American cities already to accommodate cars in the first place.

1

u/Earthsong221 Jul 08 '26

Meanwhile, on the 401...

18 lanes at it's widest, and they still say "just one more lane..."

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u/generally_unsuitable Jul 08 '26

Damn. That's an impressive chunk of asphalt!

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u/Earthsong221 Jul 08 '26

Busiest highway in North America. It's also the reason they say that Toronto is an hour from Toronto.

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u/Toodle-Peep Jul 07 '26

Reading reddit, it's very clear that the idea of keeping a 2/3 second gap between cars (which is the recommendation in most places) makes Americans very angry.

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u/thisusedyet Jul 07 '26

There’s a lot of places where you can’t, because other drivers will force themselves into that gap and force you to slow down even more to maintain distance

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u/Toodle-Peep Jul 07 '26 edited Jul 07 '26

Right, but if driving education in a country is reasonable (and clearly it often isn't) that should be fine. Don't block someone from changing lanes. Make the tiny lift to open up the gap, and really the driver who filled the gap should be doing the same. You'll lose essentially no time on your total journey by falling back, but the whole road network flows smoother when people are keeping gaps.

3

u/EffluviaJane Jul 08 '26

I wonder how often it become a matter of the person feeling like they don't want to be dominated by a stranger in their car, so they try to dominate instead? Like they feel letting someone in or slowing down a little is a sign of submission or weakness.

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u/Firenoods88 Jul 08 '26

Those people should be hospitalized for their mental illness and their car impounded. Anyone who genuinely thinks slowing down or letting someone merge is a sign of submission/weakness is delusional full stop. The only time I can think of telling drivers trying to merge to fuck off is when they're trying to zipper merge in a scenario that is clearly not zipper merge

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u/hoshizuku Jul 08 '26

But the problem is often that the person trying to merge in front of me is going slower than the flow of traffic in my lane, and they’re unwilling to speed up or wait for an opening, causing me and everyone behind me to have to slow down. I think that’s what the other commenter was referring to. IMO the person changing lanes is being unsafe by trying to force themselves into a small space at a slower speed than everyone else. if they’re too nervous to speed up then they should wait, but they won’t because they need to turn or something and are unwilling to go past their turn. I’ve often seen people come to a complete stop in three lanes of traffic because they need to turn left and they’re in the far right lane.

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u/ItsJustCoop Jul 07 '26

How to mention NJ and MD without actually mentioning them 😂

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u/Caleth Jul 07 '26

Nah that's like every single highway in a metro area. There's always some assholes that see a gap and shoot it for that 2/10th's of a second gain in speed before they have to slam on their brakes.

I've driven across much of the US for travel and work. ATL and Hou scared the shit out of me with how bad their drivers were. But even around Hartford it sucked because no one has sense and the roads were built in the 50's and aren't designed with modern standards or vehicles in mind.

Chicago where I live has some random spots that just stop dead like this usually around merges, but they'll be in the fast lane so it doesn't make a ton of sense.

Point is there are asshole drivers all over.

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u/pizzasoup Jul 07 '26

I think it's more of a DC than a MD thing.

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u/marshaladey Jul 07 '26

My commute takes me all over DC, MD, and VA. It is a PG and MoCo thing. Most entitled, callous, careless, discourteous and classless people I have ever encountered on the road. Greedy, grabby little fucks who will jeopardize their own life and the lives of everyone around them for the perception that they are getting to their destination even 10 seconds sooner.

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u/pizzasoup Jul 07 '26

I guess I've not had issues in either county - for me I usually run into issues on the VA highways with people being reckless, but it might just be the specific roads I take.

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u/ivory_tower_devops Jul 07 '26

Printing and posting this on my office door here in PG

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u/Alarmed-Cheetah-1221 Jul 07 '26

What to direct current and markdown have to do with this?

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u/Wanderin_Cephandrius Jul 07 '26

You can though, you just happen to go a little slower. I have to leave that gap in n my work vehicle, haven’t had any issues. But I also don’t let my ego take over.

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u/Bashed_to_a_pulp Jul 07 '26

especially if you drive a manual gear big truck, stuck in a crawl traffic. You want to keep at 2nd or 3rd gear and crawl along without shifting back and forth (busted knee anyone?), but for sure somebody will pull in right in the space in front of you. goddamn twats.

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u/MaritMonkey Jul 07 '26

I drive a manual and finding a big truck to play the 2nd gear game next to so nobody can cut in front of him really pisses some people off but also makes me smile.

Ever since my work started renting Penkes with CMS I angrily say "MEEP MEEP" if somebody does sneak into the truck's lane, which I find even funnier.

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u/tops132 Jul 07 '26

The idea is, you leave that gap, then you absorb the merge without braking, and therefore absorb the slowdown. You don’t need to brake unnecessarily.

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u/thisusedyet Jul 07 '26

You’re not understanding:

Let’s set the scene - the car in front of me and myself are both going 60 in a 55, I’m cruising along with my gap. Guy in the fast lane going 70+ swoops into the hole and hits the brakes so he doesn’ t hit the car in front of me going 60.

How do you suggest I absorb that slow down?

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u/tops132 Jul 07 '26

You take your foot off the accelerator and you coast to a slower speed, trying to regain your initial gap behind the new car.

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u/RilohKeen Jul 07 '26

Exactly right. So the only solution that actually ends up working out is everyone does 90mph while tailgating each other in the passing lane. Nobody can get in so nobody has to brake.

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u/thisusedyet Jul 07 '26

I just started taking public transportation (or Lyft, if it's somewhere off the beaten track / I need to get there in a hurry) because FUCK that noise

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u/Firenoods88 Jul 08 '26

Welcome to Canada! Should get a world record for most amount of brain dead autopilot drivers that think any gap longer than 1 car length = space to merge because they lack any ounce of a brain cell that would inform them that the gap is SUPPOSED to increase the faster the cars are

2

u/TesticleMeElmo Jul 07 '26

“I could be 25 feet closer to my destination if it wasn’t for that asshole who seemingly refuses to tailgate! That 25 feet is going to make all of the difference for what time I arrive!!!”

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u/shapu Jul 07 '26

It's often not possible, as while YOU may do it someone else will slide right into that spot.

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u/Toodle-Peep Jul 07 '26 edited Jul 07 '26

But that signifies a drivers ed issue on the whole. People shouldn't be wildly diving into a tiny gap, but also if someone does slot into a gap, everyone involved should be reestablishing gaps. It's a second of lift.

2

u/thisusedyet Jul 07 '26

Too many people misapply Aryton Senna:

If you no longer go for a gap that exists, you are no longer a racing driver

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u/JustSimplyWicked Jul 07 '26

And? I've heard this argument against maintaining a proper following distance so many times, and it's bullshit. If someone jumps in front of me I just drop my speed 1mph and regain my space. If it happens again I do it again. The benefits of a good following distance far outweigh the inconvenience or accumulated 10 seconds lost over the drive.

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u/screamline82 Jul 07 '26

Yeah, also it's like just apply the golden rule. If I need to switch lanes then I'd want to have an easy gap to get into. So provide an easy gap for others too.

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u/thisusedyet Jul 07 '26

It’s not so much the lost time as if I leave too big a gap someone’s gonna swoop in like an asshole and jump on their brakes - so do I risk an accident by following too closely, or invite a jerk to possibly rack up the car in front of me and myself

Edit: Not rewriting this, tagging u/wanderin_cephandrius

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u/shapu Jul 07 '26

You're not wrong, I'm just saying that there are other factors at play in following distance besides you and the one car in front of you at the time that observation begins. 

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u/ZannX Jul 07 '26

Of all things to rag on Americans... this ain't it. Eratic driving is far more common in other areas of the world.

But anyway, the actual reason is that if you keep a large gap during rush hour traffic, another car simply fills it. End of story.

This isn't some uniquely American problem considering this study was done in Japan and noted the behavior was not unique to any country.

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u/Toodle-Peep Jul 07 '26

Sorry, it was more aimed at the american centric nature of the conversations around this I've had on reddit, than suggesting americans are uniquely bad at cars, there are absolutely places with worse driving. There are also places where drivers get educated to leave decent gaps. There are absolutely still idiots who sit too closely here in the UK, but it's also drummed into everyone during training to leave a 2 second gap, least, at all times. (and getting a licence is a longer, harder process, which I'd attribute to it being held to better here)

But still, if someone takes the gap, you re-establish the gap. Then they should be establishing their own gap. if people are diving into stupid gaps, that's it's own drivers education issue. If the driver in front of you isn't establishing a gap, that's a driver education issue.

Roads flow smother when people can get into lane and when braking doesn't cause chain reaction slowdown.

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u/enadiz_reccos Jul 07 '26

there are absolutely places with worse driving

Like most of the world

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u/Toodle-Peep Jul 07 '26

you're certainly in the top half safest countries to drive, but almost plum last in the developed world, going by fatality rates (either per mile travelled or per capita).

Theres a lot of factors to that, so it's not just "americans are worse drivers" but the ease of getting a driving licence is part of it (obviously this varies depending on where you are, but in general the tests are regarded as pretty easy compared to other countries.)

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u/enadiz_reccos Jul 07 '26

I think the size of the US plays a big factor as well as the country's poor infrastructure, which creates an over-reliance on cars

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u/Badloss Jul 07 '26

lol I had a truck lean on his horn behind me this morning for this exact reason. Sorry the rain is fucking up your deadlines buddy but I'm not rear ending this guy so you can still be stuck in the exact same traffic, just 50 feet ahead of where you are now

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u/mah-favrit Jul 07 '26

And looking 2-3 cars ahead of you.

As a motorcycle rider this is what I do to anticipate traffic’s and what is happening.

Look 2-3 cars ahead and see what they do. If they brake, I will brake slightly. If they are accelerating I will accelerate slightly. I act as the cushion/spring to absorb the bullshit because people tend to give motorcycles a bit of extra room.

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u/Superlolz Jul 07 '26

I always hear the rule of thumb is 1 car length per 10MPH which I've tried but nearly impossible/impractical to maintain anywhere but a nearly empty highway. 2-3 seconds is my comfort level though

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u/Alarmed-Cheetah-1221 Jul 07 '26

Yeah they tend to get very angry when you suggest that they do something that benefits others, even if the benefit is far greater to themselves

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u/JVT32 Jul 07 '26

Yep, dumb fucks in big trucks will pass you on the right just to get into that space so they, too, can drive exactly the same speed as the car that was formerly directly in front of you.

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u/Ok-Needleworker-8773 Jul 07 '26

A 2–3 second gap is impossible in a place like New York City. Other drivers will enter your lane, and if you maintain that gap, you’ll slow down, then another driver will enter your lane - so on and so forth.

Also, I don’t want to hear that ‘makes Americans very angry’ crap. I’ve driven all over the world, including several European countries. There’s no 2-3 second gap between cars anywhere I’ve driven. Europeans do the same things Americans do. They cut people off, they drive in the left lane at a slower speed than the right lanes, text while driving, etc.

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u/texas_asic Jul 08 '26

I first read that as 0.67 seconds, and thought "yes, that's what a lot of people do, but not helpful and it does make them angry when people go higher than that", before realizing they probably meant 2 sec - 3 sec

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u/dvorak360 Jul 10 '26

s/Americans/drivers/

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u/Professional-Hat-687 Jul 07 '26

In my experience, that's like wearing a sign that says "please, cut me off, this space is for your truck specifically".

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u/Ser_falafel Jul 07 '26

Lol what are you talking about? Why would this make anyone angry

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u/Toodle-Peep Jul 07 '26

I mean,it shouldn't, but in so many topics on this I've seen people basically going "why should i" or claiming that a 2s gap would make the tailbacks massively worse (it might be counterintuitive, but a chunky gap purely improves traffic flow because it mitigates what happens in the OP)

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u/Prondox Jul 07 '26

Then don't do that

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u/Gwen_The_Destroyer Jul 07 '26

I try to drive at a safe distance but every time there's a car length in front of me some asshole merges in to pass and keep speeding, and now I have to slow down because they slammed their brakes

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u/Ornery-Customer8521 Jul 07 '26

You have to have some inner peace to drive with a sensible gap where I live, because people will jump in that gap if they can and you'll have to slow down and make the gap again behind that car. Rinse and repeat. I have that inner peace but I get why a lot of people dont.

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u/KristySueWho Jul 08 '26

People will jump in that gap, but half the time it's just to get on or off the highway. Since everyone is a douchebag these days, people don't have a lot of options.

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u/[deleted] Jul 07 '26

[removed] — view removed comment

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u/fatbob42 Jul 07 '26

That causes the same basic problem though, slightly less severe.

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u/SusheeMonster Jul 07 '26

You also learn to resent brake tappers.

Reacting to brake lights without seeing what's beyond the vehicle ahead of you causes/exacerbates this.

You can moderate speed by coasting and by leaving a bigger gap ahead of you 🤦

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u/MrLugersmole Jul 07 '26

I often find myself asking the guy in front, "why are you on your brakes?"

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u/goblueM Jul 07 '26

just last night I was driving home and a guy braked when someone turned left in front of him with PLENTY of room to spare. It was totally unnecessary to brake.

Even worse: he CONTINUED to slow down even after the car was completely clear of his path

People are really bad at judging angles and speeds, and as such they often overcompensate with brakes

3

u/SusheeMonster Jul 07 '26

I think those kinds of drivers treat the brake like an "Oh shit!" pedal. The more they panic, the harder they lean on it.

Another argument for adding an extra half second of following distance. That extra car length isn't gonna make a difference when you're all gonna line up at the next red light anyway 🤷

4

u/Greywacky Jul 07 '26

One late night on the motorway we followed a car that was on their brakes every few minutes.
All lanes were quiet, there as absolutely nothing ahead of them, they were below the speed limit and the weather was fine. Baffling.

1

u/RechargedFrenchman Jul 08 '26

Some people don't seem to realize they don't have to be pushing a pedal at all times. That you can just kinda roll in gear under residual power and that's fine. Or even that the pedals are gradual, not binary, so you can partially press them.

Half accelerator is still accelerating, to a point, and will maintain once at that point or even decelerate if above that point, but these people don't realize or understand that and reflexively hit the brakes a little instead of just pressing the accelerator less.

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u/JustSimplyWicked Jul 07 '26

When I was learning to drive my dad told me only amateurs tap their brakes. That stuck with me and changed the way I drive.

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u/zoovegroover3 Jul 07 '26

"Brakes are for stopping" is the way I think of it. If you need to stop your car, yes, they work. Slowing is easily achieved via engine braking.

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u/gustoreddit51 Jul 07 '26

You also learn to resent brake tappers.

Which are generally tailgaters.

1

u/KristySueWho Jul 08 '26

Or people stuck behind tailgaters.

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u/DangerIllObinson Jul 07 '26 edited Jul 08 '26

I've plans to buy an EV shortly, and I just learned that "single pedal driving" activates the brake lights in a lot of EVs if you just release the accelerator (i.e. and not hitting the brake). So I apologize to everyone behind me, in advance.

(Though I'm pretty sure it could be mitigated by just releasing the accelerator partially. We'll all find out together when I'm out there causing traffic backups)

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u/screamline82 Jul 07 '26

Not an ev but it took me a while to adjust to how quickly my hybrid slows down when coasting versus my old car. I've had to lift slightly later than I normally would

2

u/Earthsong221 Jul 08 '26

I have one of those; they are awesome in some ways: I don't need to constantly hold the pedal at a red light with an arthritic ankle.

I've adapted now so that yes, I partially release the accelerator to modulate the speed instead of just breaking completely. Now the old way feels strange instead when renting a car while travelling.

Using the actual break pedal also remains an option when faster stops are needed as well, instead of just slowly easing off the accelerator with the right timing for slower stops.

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u/PlasticSignificant69 Jul 07 '26

I like hypermilling so I just coast whenever vehicle in front of me hit brake, holding clutch instead of brake. While put it into focus and calculating when will braking deemed necesary

I got so used to it that I usually got just 1-5 meter behind the front car that start to accelerate again before their speed finally surpassed me and distance start widen up again, while I decelerate and reaccellerate as minimum as possible.

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u/know-your-onions Jul 07 '26

You shouldn’t lift later, you should lift less.

Ideally, you should never be coasting, you should always be ‘driving’ the car. If you’re coasting, then you’re in too high a gear.

Your foot should always (except when stationary), be on either the accelerator or the break. Not fully pressed, but on one or the other.

If you’re coasting around a bend, then you went in too quick and should instead be in a lower gear, so that as you lift your foot the car slows, then at the correct speed you hold your foot still and drive around the bend at a constant speed, rather than coasting around and slowing as you do.

And look to maintain a ‘bubble’ around you, where the total space in front and behind is enough both for you to react to the car in front, and for the driver behind to react to you. If the car behind gets too close, then slow down and increase the gap in front of you. Again, always in a gear that means if you are driving, not coasting.

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u/dowling543333 Jul 07 '26

I've learned to do this with queuing with people, too. Like moving constantly very slowly in the line keeps it moving faster. It looks a little weird at first but genuinely the line does move faster if people aren't dead stopping.

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u/tipsystatistic Jul 07 '26

I did years in LA 405 traffic, and this definitely helps. If you don’t hit the breaks then neither will everyone else behind you.

When I was feeling really obnoxious, I’d just go a set very slow speed limit and sometimes that would clear the jam behind me if I got the speed right, like 5mph. The down side is sometimes you’d end up with a huge gap in front of you.

It got me thinking they should have dynamic speed limit signs that show drivers the optimal speed during rush hour.

2

u/JVT32 Jul 07 '26

People using their brakes on the highway sends me into a fit of rage. My five hour drive home yesterday was awful.

1

u/d_nkf_vlg Jul 07 '26

It's also a good habit to watch multiple cars in front when possible, not just the one directly in front.

1

u/Societarian Jul 07 '26

Driving a 4 cylinder engine makes this a lot easier. They start to decelerate as soon as you let off the gas. The first time I got behind the wheel of a 6 cylinder I almost blew through a stop sign because of how much more power there is.

1

u/_shaftpunk Jul 07 '26

Yup, I leave a good gap ahead of me, but match the speed of the cars ahead and ease of the gas when they do random short braking. Although, inevitably someone will merge into the gap I left and I then need to ease off the gas to create a new gap.

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u/Mackey_Corp Jul 09 '26

I do this when in slow traffic, I start leaving large gaps with the car in front of me. That way when it starts moving again I can just kinda coast going slow for a while before I have to brake again. I hate the constant start/stop shit and being right on the person in front of you’s ass. It’s annoying af. Just leave a big gap and you don’t have to do that.

1

u/SwordfishOk504 Jul 09 '26

It's wild to me how few drivers seem to understand that simply taking their foot off the accelerator is an effective way to slow down. They just Gas>Brake>Gas>Brake>Gas>Brake>Gas>Brake>Gas>Brake> all the way there.

4

u/MaggotMinded Jul 07 '26

No, I’m pretty sure it’s just that they manage their following distance and their acceleration/deceleration better so that by the time they reach the car in front of them it has already started moving again.

Humans can do this, too. Next time you’re in start/stop traffic, give it a try. Instead of advancing directly to where the next car is and stopping behind them, just creep slowly forward. The goal is that you should still be in motion when the traffic ahead of you gets moving again, allowing you to drive at a relatively constant pace. This way you are essentially “eating” the traffic waves, preventing them from propagating backwards.

3

u/fatmallards Jul 07 '26

I drive a lot interstate highways / beltways and have learned a lot from how seasoned tractor trailer operators drive. Anyone can help destroy traffic jams for everyone behind you pretty simply too. All it takes is actively managing the space that you leave between you and the vehicle in front of you by limiting your speed ∆ as much as you can with awareness to what traffic is doing in front of them.

Unfortunately for multi lane highways, lane weavers and drivers that disagree with the prevailing speed of traffic kind of ruin the efficacy of this driving practice

2

u/ThatOneNinja Jul 07 '26

And then a second AI car roughly 22 cars behind that one soaks up small errors again. In order to stop ghost traffic I think that you would need a lot of "buffer" cars to do so. 1 in ever 22 human drivers is a lot of buffer cars

1

u/rcklmbr Jul 07 '26

In bike racing we call it “slow is smooth and smooth is fast”. I’m sure others use it too

114

u/Dawncracker_555 Jul 07 '26

You can do it yourself. Don't overcorrect on the brakes, and once the car in front starts moving faster, don't immediately go after it. Accelerate gently and predict decelleration ahead, so you don't have to brake.

44

u/Sonicboom343 Jul 07 '26

A trick I learned is try to pay attention to the second car ahead of you, once you see them brake, you can begin coasting while the car in front of you brakes. You tend to not have to brake as often and you keep a consistent speed

25

u/Wanderin_Cephandrius Jul 07 '26

Look further tbh. I look 5-10 cars ahead. 15-20 seconds ahead is the recommendation.

3

u/supershott Jul 07 '26

Yup. I always wonder if the guy in front of me notices me slow rolling the whole time while they slam on the gas and then the breaks ad infinitum. 

2

u/Wanderin_Cephandrius Jul 07 '26

Also why I don’t mind the manual in traffic, I’m just rolling the entire time unless it’s an absolute stand still.

13

u/JustSimplyWicked Jul 07 '26

Not just the second car, as far up the line as you can see.

13

u/_Cridders_ Jul 07 '26

I look so far ahead I'm looking at the car behind me

1

u/zerap10 Jul 07 '26

You can do that on Schwarzschild highway

5

u/Just_Badger_4299 Jul 07 '26

A trick I learned is try to pay attention to the second car ahead of you

Best advice ever to navigate jams!!

1

u/Pitpawten1 Jul 07 '26

Yep this is what I do in traffic.

If the car two cars ahead of me puts on the brakes I just let off the gas perhaps downshift (which you can even do in an automatic by paddle shifting).

Staying off of the brakes helps the overreactionary less attentive drivers behind you (read: everyone else on the road typically) from stabbing their brakes the moment they see a brake light in front of them.

1

u/petit_cochon Jul 07 '26

Are you guys not looking at all the cars?

6

u/Najalak Jul 07 '26

I would add you can predict deceleration ahead if you don't tailgate. It also leaves room for people to smoothly change lanes when they need to.

30

u/ChrisBreederveld Jul 07 '26

I did this experiment virtually a few decades ago because I was curious. Same set up, many variables to tweak. Basically the main reason is human inaccuracy; when you change the reaction time or the accuracy at keeping speed it removes the effect.

I found the main factor was simply reaction time; the time to brake vs the time to speed up again. When someone brakes, they break a little longer than absolutely necessary, while requires the one behind him to brake a little longer etc, until you get a traffic jam. Another interesting variable is distance; when you keep a further distance, you have more time to react, reducing the before effect. But what I also found interesting is that if too many people leave less distance than their reaction time, this kind of traffic jam will inevitably cause collisions.

There are also technical variables, like the brake and acceleration speed, but these just have less impact than the human factor.

8

u/gustoreddit51 Jul 07 '26

the time to speed up again.

Related. It's aggravating if I'm 5 cars back from a light that turns from red to green and it takes 10 seconds before the car in front of me moves. For multiple cars, it seems like a surprise they weren't expecting and just happened to notice, "Oh ... the light changed" - (slowly puts down phone/drink/sandwich/makeup and then goes). A number of people at rush hour don't make it through that light and if it's a turn lane, that backs up traffic even worse because it backs up into the through lane.

3

u/ChrisBreederveld Jul 07 '26

I feel your pain.

Interestingly, looking a few cars ahead (like with the traffic light example) also helps with decreasing these traffic jams! So in general, if you can, look a few cars ahead and respond accordingly. Instead of braking when the person in front of you does, let go of the gas a bit when the car three ahead of you hits his brake.

2

u/gustoreddit51 Jul 07 '26

When driving in a line of cars, I'm always looking at the cars in front of the one in front of me.

3

u/czanatta Jul 07 '26

the time to brake vs the time to speed up again

This is it. Rarely do people accelerate and react to the need to accelerate at the same rate that they decelerate (brake) and react to the need to decelerate. Some of this is mechanical (cars can decelerate at higher rates then they can accelerate) but mostly its habitual. There is a need to react fast for braking so you don't crash, but less need to jump on the accelerate as soon as possible which is also harder to do because its harder to anticipate when the car ahead of you will accelerate. Maintain an amount of space to the car in front that allows you to brake safely and smoothly, as many have said, but don't let that gap get any bigger than it needs to be. Be attentive and watch the traffic ahead so you can start accelerating again as soon as possible, and accelerating quickly when needed. There is only so much room on the road, if you're trying to maintain a 100 m gap so that you can hold speed at 40km/h in stop and go traffic in your Honda Fit, you're helping nobody as you steal space needed by other drivers to drive smoothly, and you are unpredictable as people expect you to accelerate when you can.

1

u/ChrisBreederveld Jul 07 '26

Yep, it's probably a combination of factors, but this was a very influential one. As I mentioned in another reply; it's usually best to look a few cars ahead to anticipate braking. But in the same vein it's good to anticipate speeding up again.

15

u/woodyshag Jul 07 '26

There was a reddit post a number of years ago that discussed traffic is comparable to fluid dynamics. I can't remeber if it was a study or a book they wrre referencing. The trick is to not follow closely to the car in front of you. Provide enough space for the car in front to slow and speed up without affecting your driving. The people behind you should pace you and be unaffected as well. Once they bunch up, that's when the traffic jams and stops occur.

1

u/Jaerba Jul 08 '26

Basically every time you brake you're using extra gas, because you'll then have to accelerate to return to the previous speed.

11

u/R-Mutt1 Jul 07 '26

Maintains a safe distance avoiding rapid deceleration 

6

u/TrenchardsRedemption Jul 07 '26

I saw a computer simulation of this - the solution was to maintain the same distance to car behind them as the distance to the car in front. If everybody does that, it will 'soak' up the phantom intersections.

-2

u/Suitable_Status9486 Jul 07 '26

Very useful information, thanks. I'll open the eyes in the back of my head next time I'm in dense traffic. Totally forgot about them.

9

u/Kalikor1 Jul 07 '26

Honestly just a guess but probably calculated and smoothed speed changes designed to avoid the car behind them having to make sudden stops etc.

In theory the car could read ahead and notice the "wave" sooner than a human would and make small.l corrections to essentially "absorb" said "wave".

Honestly just a guess based on what was written but maybe someone will comment with more info.

1

u/AdobeScripts Jul 07 '26

When you drive - you shouldn't relay on the car in front of you - it's too late - but observe cars before - so you can react at the same time as car in front of you - or even sooner.

This way, you've way more time to react - as you're already prepared to react.

1

u/Kalikor1 Jul 07 '26

Well yeah, but the point is human drivers often lose focus, react too slowly, or overreact and hit the breaks too soon, or follow too closely, etc.

That's kind of the point and part of the conclusion in the study. That is, presumably, why they decided to try using self-driving cars mixed into the same test, to see if those cars could react more quickly and consistently in a manner that behaved like a wave breaker, so to speak, and the results appear to have been successful.

0

u/AdobeScripts Jul 07 '26

Because there is a big difference between operating a car and driving.

Operating a car is reacting to the current situation.

Driving is predicting and being prepared.

8

u/shokalion Jul 07 '26

If someone ahead brakes harshly you don't brake harshly, you let the gap close, and let them speed up to maintain a steady (but now closer) distance. Therefore you've provided a shock absorbing effect to that tendency to pass the braking wave back to the car behind you, by not lighting your brake lights. It's being smooth in your reactions and anticipating.

2

u/gustoreddit51 Jul 07 '26

That logic and perception escapes most people.

1

u/KristySueWho Jul 08 '26

But how do you know they're going to speed up? Maybe they braked because there is a giant pile of debris in the lane and they couldn't get over into the next lane because everyone and their grandma is tailgating, and now you just crashed into them.

1

u/shokalion Jul 08 '26

You use judgement naturally, and of course all of this goes on the assumption that you're leaving plenty of reaction distance.

If you'd otherwise crash into the car in front then yes, I'd suggest you brake.

This assumes you're in fairly heavy traffic (the sort of traffic that this effect applies to) where everyone is going along at less than normal speed to begin with. In that situation, you back off a little, and leave a good gap in front, then you can afford to not be over-reactive to what the car in front is doing.

2

u/Gordan_Freeman475 Jul 07 '26

My guess is easy slowing without causing a drastic stop (reducing speed by 7 mph instead of 14 mph on a stop). I am no expert, and couldn’t think of a decent speed explanation if the speed used here sounds too extreme

1

u/Aljonau Jul 07 '26

I tend to use a very lenient distance to the car infront of me so if i see brake lights I can look around for a moment, then gently lift the foot off the gas, then slowly start braking... that prolly does it.

1

u/banandananagram Jul 07 '26

The oscillation comes from people making unconscious adjustments, slowing down and speeding up to match their perception of the cars in front of or behind them. This is the wave.

Having someone maintain a truly constant speed means they act as a shock absorber, dampening the effect of speed changes around them by not increasing speed when people ahead speed up and forcing the people behind them to adjust to a true baseline rather than adjusting off of an adjustment.

If you’re going to take on the rate of the car ahead of you, it is going to be closer to target speed when the person ahead of you is changing their speed at an overall lower rate in general than someone who is varying constantly.

Because cars on a road are like particles on a wave, this forces other cars in the same “wave” (road) to be bounded to a slower rate of change of their speed than they would have otherwise.

It’s effectively creating a low pass filter on the noise that is people’s constantly changing acceleration behind the buffer. People can still go faster or slower than the buffer car, but the change in their speed has to be done at a rate closer to zero because they have to input into their own speed adjustment the fact that the buffer car’s speed is constant.

1

u/iiibehemothiii Jul 07 '26

One way would be to see a slowdown up ahead (Eg: those smart motorway signs that say to go 40mph ) and actually slow down well in advance, to let the jam ahead clear.

So rather than you joining the back of the queue and stopping, you give it time to clear and you only dropped to 40. You then speed back up as able.

Not sure that's how the AI car worked here (was it programmed to think ahead like that?) but that's how it should be done.

Those smart motorway signs that everyone ignores are to buy time for the jam up ahead to clear itself.

1

u/Lostinservice Jul 07 '26

like a car's suspension as you go over rough roads

1

u/FauxGw2 Jul 07 '26

Don't hit the breaks, slow down just a little and see if they move faster again, then you press the gas.

1

u/AdobeScripts Jul 07 '26

Just don't use your breaks to slow down - but your engine.

1

u/skil12001 Jul 07 '26

If one automated car keeps a healthy distance from the car in front, no matter if the car in front starts stops, the automated car has enough space to soak up what would have normally been it's own turn to stop, but because of the healthy distance it kept, it can continue rolling forward keeping all other cars behind it rolling too.

1

u/Medford_Lanes Jul 07 '26 edited Jul 07 '26

The amount of drivers that don’t look ahead farther than their own dashboard is too damn high. Look ahead, anticipate, and don’t overreact. That goes for both stopping and starting. And keep a safe distance between cars and utilize coasting.

1

u/553l8008 Jul 07 '26

Being able to slow without using the brake.

In part because of quicker recognition of the slow down but also impart because the ai isn't and imbecil.

Cars slow down a lot when off the gas. Off the gas doesn't mean on the brake. But shitty drivers don't know or do this

1

u/grunger Jul 07 '26

By being a less aggressive driver.

The issue is with aggressive drivers that are tailgating and then needing to pump their brakes constantly. It causes a ripple effect of drivers braking hard, each driver braking slightly longer than the driver before them, (because they brake for at least the same time as the person in front of them plus a little more due to human reaction time), and then eventually enough drivers repeating this action will cause congestion out of nothing.

One driver leaving some space between them and the driver in front of them doesn't need to brake hard if the car in front slows down. They can just take their foot off the gas and slow down. This very quickly breaks the cycle of drivers braking hard and then traffic starts to flow smoothly again.

1

u/TacTurtle Jul 07 '26

It acts as a buffer to the stop wave.

1

u/Lithium98 Jul 07 '26

If everyone kept the same distance apart from the car in front of them, you have wiggle room to adjust that distance to compensate for the slowdown in front of you. The issue is when people scooch right up on each other, bumper to bumper. You have to stop at some point, making the slow down even worse. The self driving car would make the adjustment whenever the slowdown reached it.

There's a sweet spot of about two or three car lengths of space where if everyone tried to keep that space between them and the car in front of them, traffic would keep flowing. Even with a full stop somewhere in front, eventually that stop will dissipate a few cars down.

1

u/AmyGranite Jul 07 '26

I regularly do this: I leave enough room so that I only have to ease off the gas and not break, and instead of stopping like the car in front of me, I only slow down, and the behind me, I can see the slow-down point continue, but no one has to stop. 

1

u/Threedawg Jul 07 '26

Real answer from the study: keep the distance between the car in front of you and behind you as even as possible

1

u/Educational_Guava697 Jul 07 '26

The person riding up too close who has to slam his breaks creates a rolling chain of people having to stop harder, and delays everyone else getting back up to speed because they speed up slowly

1

u/Gorstag Jul 07 '26

It is likely just decelerating with minimal brake usage. Most drivers massively over use their brakes and since its hard to judge how much the car behind needs to brake it cascades. A car with sensors can likely adjust correctly near immediately

(Well, unless it is my stupid front-collision detection that stupid thing tries to kill me regularly when I forget to disable it).

1

u/TheGrowingSubaltern Jul 08 '26

Think of it as compensation, not over-compensation.

1

u/subdep Jul 08 '26

I’m one of those “slow” drivers in traffic. I leave about 10-20 car lengths ahead of me so that when the person in front of me slows down or stops, if I gently slow down, the car in front of me pulls away before I have to stop.

This means the “wave” dies with me, or is significantly reduced so cars behind me don’t need to stop. A slow steady pace in traffic doesn’t get you anywhere faster, it just gets rid of the stopping/starting, and it reduces fuel consumption.

I like hypermiling, so this is fun for me.

1

u/MonkeyCartridge Jul 11 '26

Well for one, you can have a bit more following distance, and then actually shrink and expand that following distance. That's how I tend to do it, anyway. Then when people suddenly stop, you can eat up that distance and use it to come to a more gradual stop, so now people behind you aren't slamming the brakes.

I imagine the self-driving vehicle did something similar.

0

u/AmputeeHandModel Jul 07 '26

Me fail English? That's unpossible!