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Experiment Shows Traffic 'Shock Waves' Cause Jams

Zonk posted more than 6 years ago | from the science-in-the-wheels dept.

Japan 642

Galactic_grub writes "Japanese researchers recently performed the first experimental demonstration of a phenomenon that causes a busy freeway to inexplicably grind to a halt. A team from Nagoya University in Japan had volunteers drive cars around a small circular track and monitored the way 'shockwaves' — caused when one driver brakes — are sent back to other cars, caused jams to occur. Drivers were asked to travel at 30 kmph but small fluctuations soon appeared, eventually causing several vehicles to stop completely. Understanding the phenomenon could help devise ways to avoid the problem. As one researcher comments: 'If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred.'"

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Brakes. Not breaks. (4, Informative)

caluml (551744) | more than 6 years ago | (#22635528)

1. It's brakes. Brakes. Breaks is when something stops working. 2. This is obvious to anyone who has driven much. Try not to use your *brakes* on the motorway. Try to "iron out" the waves by ever so slowly dropping back when you see them approaching.

Re:Brakes. Not breaks. (3, Funny)

wattrlz (1162603) | more than 6 years ago | (#22635554)

Well, it's an understandable mistake. They're, "Breaking" the flow of traffic, after all.

Re:Brakes. Not breaks. (0)

Anonymous Coward | more than 6 years ago | (#22635828)

well, it's their braking that is causing the breakage in the first place...

Re:Brakes. Not breaks. (2, Insightful)

bassgoonist (876907) | more than 6 years ago | (#22635578)

If someone breaks their car I'm sure it could cause traffic to stop moving...:-P

Re:Brakes. Not breaks. (0)

Anonymous Coward | more than 6 years ago | (#22635610)

Yeah, I always thought this was fairly obvious. If heavy traffic is moving smoothly at 70 mph, and one person slows down inadvertantly to 65 mph, the driver behind him would overcompensate and slow to 60 mph. In heavy enough traffic, this would eventually lead to drivers being completely stopped. Annoying? Yes. Scientific breakthrough? No.

Re:Brakes. Not breaks. (5, Interesting)

Yold (473518) | more than 6 years ago | (#22635654)

Tailgating is a problem too. It really pisses me off, that even in non-rushhour traffic, some idiot is always less than a car-length off my back end. Leaving a buffer zone allows you to avoid using your breaks when traffic slows.

I wonder how much aggressive driving (someone speeding up to 90, and then cutting in front of you for seemingly no reason), contributes to breaking shock waves. I've seen it happen often enough where someone will make an unnecessary maneuver to get 30 feet ahead of traffic.

Re:Brakes. Not breaks. (5, Insightful)

Strawser (22927) | more than 6 years ago | (#22635902)

It's a combination of people who ride slow in the left-hand lane and speeders. The people (whom I'd like to shoot) that pull over to the passing lane and then drive the same speed as the car to their right cause rolling road-blocks. When faster-moving traffic inevitably catches up to them, it can't pass, so it builds up into a massive pack of slow-moving crap. Then, sooner or later, someone taps his brakes, and then the one behind him does it just a bit longer, and so on and so forth, until there's a stop for no reason. Meanwhile, the jerk-off in the left hand lane at the head of this rolling traffic jam is still doing just fine at 50 MPH.

If police would enforce rules against driving too slowly (generally defined as being passed on the right (because if traffic is passing you on the right, then you need to get the fuck over)) as they do aggressive driving, the problem would be much less prevalent. Then, the faster moving traffic could pass the slower moving traffic, keep on going, and there wouldn't be any problems. Sadly, though, that's not the case in any metro-area I've dealt with. Instead, the jerkoff Sunday Driver creeping along at 50 in the passing lane just has to be dealt with, usually by getting around him in the right hand lane, then speeding up to 90 and cutting in front of him so you can pass the traffic on the right.

Re:Brakes. Not breaks. (2, Interesting)

T-Bone-T (1048702) | more than 6 years ago | (#22635998)

Sadly enough, getting passed on the right can't be reason alone for a ticket. While I was moving, I had to block traffic with my car so my parents and my stuff could move back over into the left lane. They passed a slow truck and everyone was so impatient to get around they just started squeezing by on the right until I got in their way.

Re:Brakes. Not breaks. (4, Insightful)

sm62704 (957197) | more than 6 years ago | (#22636062)

Tailgating is THE problem.

I try to stay far enough behind the car ahead of me so that when he brakes, I merely have to remove my foot from the accelerator so I don't convert my kinetic energy to heat. Of course, some dipshit always sees the three car length hole in the thirty mph traffic (you're supposed to maintain 1 car length for every 10mph anyway but none of the fucktards in Springfield do) and fills it in.

If people maintained a reaonable distance (the 1 car lenhgth for each 10 mph) you wouldn't have this effect, or if it occurred it wouldn't be so bad.

Every time you touch your brake for any reason whatever you throw fuel away as waste heat.

<jk>(global warming comes from the hot air blowing out of the world's capitols)</jk>


Re:Brakes. Not breaks. (-1, Troll)

chakan2 (1106731) | more than 6 years ago | (#22636084)

As a representative of the asshats that tailgate...try to go a little faster than the speedlimit in the left lane, you won't get tailgated as much.

Re:Brakes. Not breaks. (4, Funny)

0100010001010011 (652467) | more than 6 years ago | (#22635694)

Dude, don't loose your mind. I was just making a joke up they're. If you come off you're rocker that quickly I wonder what you have up their in your noggin. Sounds like a screw lose or something. I mean I didn't try to effect you in anyway, but now look how you've gone and disrupted the affect the original poster had. Here me out, there are a lot of people that are knew hear. You should calm down than come back later.

(stolen from myself [] )

Re:Brakes. Not breaks. (4, Funny)

The Night Watchman (170430) | more than 6 years ago | (#22635980)

Damn you, sir! That post managed to hurt my brain even when I knew it was meant in jest. Grammar... terrible... must... correct...

Congratulations! (1)

illegalcortex (1007791) | more than 6 years ago | (#22635702)

Your astute criticism seems to have accomplished the unthinkable - a slashdot correction. At least this is my assumption, since other people also quoted the original "when one driver breaks" phrase.

Amazing that they will fix this but often leave completely inaccurate articles uncorrected.

Re:Brakes. Not breaks. (1)

CmdrGravy (645153) | more than 6 years ago | (#22635842)

Exactly, the most annoying people are in the world are the ones who are constantly touching the brakes on the motorway because they are unable to judge the speed of the traffic in front of them properly because you have to leave a massive gap behind them which people then jump into and also begin to randomly break when the guy in front of them gets back up to his tricks again.

In Soviet America: (0)

Anonymous Coward | more than 6 years ago | (#22635988)

Jams cause shock waves.

Vote: Communist to save democracy

Filipino Monkey

Interesting, but not a solution (0)

Anonymous Coward | more than 6 years ago | (#22635544)

UbuntuDupe [] here, posting AC because some errant mods have been going through my history to mod me down long after the fact.

Anyway, I think research like this is interesting, but I strongly caution people against reading too much into it. What I mean is, this doesn't fundamentally make road travel in dense areas more efficient long-term. Even if you were to implement the cars that drive themselves and could have any driving algorithm and eliminated all of these unnecessary jams, the actual effect would be,

"Hey! Check out $CITY! Their highways are ultra-efficient! Let's all move there!"

The higher capacity simply draws more people to relocate such that they depend on that capacity, eventually using it up and bringing you back to square one. This has happened everywhere roads have been expanded.

Furthermore, keep in mind that not all roads can be highways or freeways. Eventually, roads have to "dump their load" onto streets of lower density. No matter how efficient you make the big roads, if you're over the capacity of the small roads, you'll simply cause a backlog and jam as people go from the big to the small.

Now, before you rip my head off, let me just say, I'm not suggesting that we just throw up our hands and do nothing, never expand roads, expect people to stick in existing arrangements. What I'm saying is, you can't solve the problem of traffic unless you fundamentally change the incentives drivers face with respect to driving. That is why I suggest [] having tolls at peak times (and *only* at times where there would be traffic jams) sufficient to let the traffic flow and thus making people avoid the travel, or travel more densely, to make the roads actually work and not sacrifice tons to time in traffic.

Of course, this won't happen, because (like people in former communist countries) people have a deep resistance to paying for a scarce good (highway usage at peak times) that they are accustomed to being "[monetarily] free", even if it does save them hours of valuable time every day. Furthermore, for most couples with children, and chime in if you are one, the difficulty of traveling to and from your home, is a *feature* rather than a flaw -- you don't want people to be able to easily take a bus to a place near your home.

So, traffic wave research is interesting, but don't expect it to be a cure-all.

Re:Interesting, but not a solution (5, Interesting)

FuzzyDaddy (584528) | more than 6 years ago | (#22635880)

As someone who has been commuting at least 45 minutes for most of my career, I've had a lot of time to think about traffic. I've always thought that traffic can be compared to a phase transition, such as ice freezing. Now this is fuzzy, I haven't done mathematical models or anything.

Breaking or other external factors (an accident or flashing lights by the side of the road) can certainly precipitate a change from a swiftly moving flow to a slow moving flow. However, they only cause a transition when the density is high enough. If there's an accident during a low traffic time, you whiz by it. If they close two lanes out of four, and it's low traffic, you get a little backup, but it reaches a modest steady state size in low traffic. In high traffic you get a "wave" - the backup moves steadily backwards from the scene of an accident, and remains after the accident clears.

I often tell my wife that I can tell if a slowdown is just due to high volume or an accident by the abruptness of the slow down. An abrupt slowdown, I think, means heavy traffic "precipitated" into a jam by an external event.

So braking as described may be a precipitating event, but it's the sensitivity of the traffic flow to it that is the fundamental issue. I'd guess that even if people didn't brake so much, in those sensitive conditions a fender bender by the side of the road could cause a major backup.

(Clearly, I've thought about this WAY too much.)

Re:Interesting, but not a solution (1)

PoliTech (998983) | more than 6 years ago | (#22636040)

Might I suggest that people use something completely crazy, like public transportation?

While I too would like to see improvement in the streets and roads infrastructure, the problem here is NOT with the infrastructure, it societal and anthropomorphic. The issue is not overall capacity; most roads are nearly deserted during certain parts of every day.

Society requires that the populace generally start and finish work at roughly the same times daily. Human nature and our anthropomorphic instinctive reactions while traveling as it turns out, is primarily responsible for traffic jams.

Increasing taxes while providing no alternative means of transportation is not really an answer, it's just an excuse for another governmental cash grab. The transportation problems and requisite solutions are quite a bit more complex than that.

"Charge a toll" is simplistic at best, penalizes the productive for their productivity, and is simply counterintuitive to what you say you would be trying to achieve. To say that a toll would "save them hours of valuable [commuting] time every day" might not necessarily be the net result, because those same workers would have to spend work hours to pay for the tolls, while at the end of the day they may still find themselves sitting in the same traffic.

Re:Interesting, but not a solution (1)

j-pimp (177072) | more than 6 years ago | (#22636134)

Furthermore, for most couples with children, and chime in if you are one, the difficulty of traveling to and from your home, is a *feature* rather than a flaw -- you don't want people to be able to easily take a bus to a place near your home.

I see a logic flaw here. I'm well aware of the "think of the children/not in my back yard" mentality that says "I don't want a bus stop near my home" and it has some merit. However, the people I don't want near my home are not necessarily traveling a great distance, and can easily take local roads that are not subject to a great deal of rush hour crunch. Also, most of those concerns are best dealt with by making sure their are responsible adults around, be they relatives, neighbors, or paid caregivers.

Also, kidnappings and break ins tend to occur in the small hours when their is little traffic.

That's why I never use my brakes (4, Funny)

Reality Master 201 (578873) | more than 6 years ago | (#22635550)

I have respect for my fellow drivers, and only use the gas pedal. Breaking is for pussies.

Re:That's why I never use my brakes (1, Funny)

Anonymous Coward | more than 6 years ago | (#22635642)

Apparently spelling is for pussies too.

Re:That's why I never use my brakes (5, Insightful)

afidel (530433) | more than 6 years ago | (#22635728)

Actually if you're following at the correct distance you shouldn't need your brakes in all but the most extreme situations like getting cut off. I know I try to minimize breaking most of the time and in non-gridlock situations I can keep from touching my break pedal probably 80% of the time when the car in front of me touches theirs. It requires looking several cars ahead and easing off the gas well ahead of the ripple location but if more people drove like this I bet most of those stupid sudden stop points could be eliminated.

Re:That's why I never use my brakes (1)

jdavidb (449077) | more than 6 years ago | (#22635866)

I follow the rule of taking my foot of the accelerator at a "yellow light condition" and hitting the brakes at a "red light condition." A yellow light is obviously a yellow light condition (unless for some other reason of safety I need to start hitting the brake), but several other things are "yellow light conditions" to my brain and this actually makes my driving real smooth: if the brake lights of the car two cars in front of me come on, that's a yellow light condition. If the turn signal of the car in front of me comes on, that's a yellow light condition. And if I'm in a situation where I want to get over a lane or the lane near me is ending, cars in that lane that are further ahead of me are also considered to be the car in front of me/two cars in front of me as appropriate. (A sort of logical OR occurs in my brain considering the cars in my lane + the other lane in question.) The brake lights of the car in front of me coming on is a "red light condition."

The practical upshot is I don't have to hit my brake as often, and when I do I've usually already slowed down to a much safer and smoother speed for braking.

Re:That's why I never use my brakes (2, Insightful)

coop247 (974899) | more than 6 years ago | (#22635768)

In case it hasn't already been said, GET OFF YOUR F***ING CELL PHONE AND DRIVE MORON. Whew, needed to get that off my chest.

Re:That's why I never use my brakes (1)

Ngarrang (1023425) | more than 6 years ago | (#22635840)

I try to maintain a safe distance in front of the cars behind me at all times through the proper application of the gas pedal.

I just wish that more Americans followed the concept of "Drive Right". The far left lane is NOT for doing the post speed limit or less. Oh, and that turn signal thingy...try using is occasionally.

Sorry, I will stop ranting now.

no such thing as perfection (1)

LiquidCoooled (634315) | more than 6 years ago | (#22635552)

There is no such thing as perfection.

If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred.

If they had done this, there would have either been a big pile up as the combined error causes one car to go into the back of another, or if they put a feedback loop altering speed then they would have also had these jams.

Re:no such thing as perfection (4, Insightful)

RyuuzakiTetsuya (195424) | more than 6 years ago | (#22635598)

You're missing the point of the experiment. Yes, in reality, something like that is incredibly likely. But the idea here is to study the effects other humans have on each other in dense driving situations.

Re:no such thing as perfection (1)

LiquidCoooled (634315) | more than 6 years ago | (#22635646)

Its not humans, its feedback in general.

Computers, robots, ants, elephants and fish would all do the same based upon feedback.

Re:no such thing as perfection (2, Insightful)

gwait (179005) | more than 6 years ago | (#22636074)

Agreed, this is a classic feedback loop control problem, nothing really new at all, except that an electronic control system could easily iron out the resonances in this case. []

In the human case the basic problem is with reaction time, a little worse than a tenth of a second.

Say a driver slows down for 5 seconds then returns to normal speed. The one right behind him has to slow down, but takes a tenth of a second to respond. The one behind him also has to slow down, now two tenths of a second later than the originator, and so on, by the time you get one hundred cars back the slowdown is 10 seconds behind the original event. The slowdown event in this case travels backwards like a wave at a rate of a tenth of a second per car "space", which is the car length plus the gap that the driver leaves in front of his car for safety.

If the slowdown wave travels backwards at the same speed that the cars are driving, you get one of those annoying events where everyone has to slow down at the same point on the highway (because the car in front had to slow down and so on), but there seems to be no reason for the holdup.

Being humans, the model is a poor approximation, some drivers might see the brake lights of a few cars ahead and react sooner, others are busy talking on cellphones and react later etc..

A reasonably well designed computerized driving system could easily remove the resonances, reacting far faster than humans, it would not be too difficult to design one that reacted in less than a millisecond or better.

I'm surprised the researchers seem to be discovering this now? Anyone bored and stuck in this kind of stop and go traffic on a freeway (and a little bit observant..) would have noticed this long ago.

Re:no such thing as perfection (1)

digitalaudiorock (1130835) | more than 6 years ago | (#22635916)

Here's an interesting related theory that definitely affects traffic: []

Apparently you perceive cars passing you differently than those you pass, causing you to always think the "other lane" is faster.

The real point... (1)

crh3675 (874238) | more than 6 years ago | (#22635956)

Actually, the real experiment results were to show that the Japanese also understand Newton's Law of Motion. Humans are just the catalyst. I wonder who paid for that stupid experiment?

Re:no such thing as perfection (3, Insightful)

Goffee71 (628501) | more than 6 years ago | (#22635620)

The M25 they mention isn't a perfect circle, which is a shame and most non-android drivers studiously ignore the speed restrictions until everything grinds to a halt. Its either 80 or nothing on the road and all the science in the world won't help.

There is such thing as logic, which doesnt need it (1)

poetmatt (793785) | more than 6 years ago | (#22635864)

You do realize that speed limits are not accurate [] , right? The only reason they are there is to monetize away your driving privileges that they granted to you in the first place. In reality, the minute you have a drivers license, you just lost a ton of rights on the US.

If people realize that the reason the world goes 80 instead because that is the natural point that people feel safe to drive given current conditions and someone wasn't driving in the fast lane (going excessively slow and causing the feedback), such a situation wouldn't occur.

Exactly as someone else said, this is not automotive specific, and the only solution to excess feedback is to reduce whatever is slowing things down, not to "slow things down further". If roads were unrestricted for speeds and had more lanes people would go 100+ more frequently (and more safely), of course roads would wear faster among other things like that.

Additionally, this feedback driving creates a "safety-minded" driver, aka someone who drives so slow in the snow/rain/etc that it creates pileups for hours. "I see a drop of rain on my windshield = lets drive 15 under the limit (as if the limit wasnt bad enough)" = feedback at its finest.

Re:no such thing as perfection (1)

mwvdlee (775178) | more than 6 years ago | (#22635966)

Given robots with perfect behaviour, they'd still have to change speed if other perfect driving robots got on the road at a junction.

Re:no such thing as perfection (1)

_14k4 (5085) | more than 6 years ago | (#22636002)

To be honest, the only reason the Japanese researchers want more robotics driving is because they all look damn hot. I think it's a Japanese thing - we have real-dolls, they have robotic women who can cook, clean, and apparently drive. :P

Linux (0)

Anonymous Coward | more than 6 years ago | (#22635560)

Is this what happens when I start up an application in Linux and it thrashes the drive for ages?

Faulty drivers (4, Funny)

mhifoe (681645) | more than 6 years ago | (#22635566)

caused when one driver breaks
Maybe some more reliable drivers would have made the experiment more successful.

Re:Faulty drivers (0)

Anonymous Coward | more than 6 years ago | (#22635704)

> Maybe some more reliable drivers would have made the experiment more successful.

Maybe some more reliable drivers on real roads would make for fewer traffic jams.

Oh, wait----

Never mind

"caused when one driver breaks" (5, Funny)

Kingrames (858416) | more than 6 years ago | (#22635574)

Well there's your problem right there.

You wouldn't have this problem if you wrote your own drivers.

physorg (4, Informative)

_14k4 (5085) | more than 6 years ago | (#22635580)

It's already been done here, on Slashdot - already solved [] by the math guys, outlined on physorg.

But really any time I can see math at work in my day-to-day commute, is a good day to me. Also, it's fun to reach out and "touch" the asshole 200 yards behind you...

Re:physorg (2, Insightful)

RyuuzakiTetsuya (195424) | more than 6 years ago | (#22635660)

Yes, and the other part of science is...


By the look of it, it looks like these researchers confirmed what the mathematicians predicted would happen. Someone brakes too hard, or too early, and the rest of the flow of traffic behind them is now all fucked up.

I swear, I've seen people bitch that "oh, problem could've been busted on mythbusters if they just did the math and left it at that" and not realize that the follow through is to... DO THE EXPERIMENT. Science occasionally is fun work out in the field and not just theoretical models.

Re:physorg (2, Insightful)

_14k4 (5085) | more than 6 years ago | (#22635978)

I mentioned no such nonsense... I was reiterating that it was shown, mathematically... and my reply stated that "omg I enjoy it when math backs up real life. btw here is the physorg link." I didn't really bitch about /. reprinting a story, or "old news" and all of that.

Frankly, I think the only reason one could do this experiment is for the excuse to drive little cars in the name of science.

So, quityerbitchin' and realize that I was backing up the experiment with math.

Re:physorg (0)

Anonymous Coward | more than 6 years ago | (#22636090)

Or just ask people working in office building along the roadway ... I used to work in one overlooking Central Expressway in Dallas and always got a kick out of watching the idiots that zoomed and stopped, zoomed and stopped ... those lanes always moved slower than the ones with the laid back drivers that coasted from one slowdown to another

Re:physorg (2, Informative)

Lumpy (12016) | more than 6 years ago | (#22635756)

Yup and researched and discovered more than 5 years ago. Unless there is something vastly different from Japanese drivers compared to the drivers here in the usa it's simply confirmation that the research done by grad students here is 100% correct.

Anyone that has paid attention and driven in heavy city traffic has seen this. The hill coming into detroit on I96 you can watch in the early morning a wave of breaklights coming to you from a mile away. the undulation continues for the next 30 miles and probably lasts for most of the commute times.

Re:physorg (1)

dyslexicbunny (940925) | more than 6 years ago | (#22635844)

Yea, I thought I'd seen this before here and other places including this simulation [] (java warning). A lot of the modeling is interesting because it simply captures a lot of the real behavior you see every day.

A couple of early posters are making jokes about faulty drivers and writing your own. But honestly, eliminating the human component from driving would significantly improve traffic flow across the board and would allow it to be optimizable. It's really just the problem of so many different drivers making such a system a complete failure - it's like General Motors and their 31 different models (gratuitous car analogy). But until people become less lawsuit happy and unless such a scheme can work with people that want to drive, I doubt that such a system could be implemented. It's far more likely that we'll see passive incremental improvements such as intelligent braking instead of more active disruptive improvements like auto-drive.

Even older than that (2, Interesting)

Scareduck (177470) | more than 6 years ago | (#22636086)

I read a study prepared for Caltrans back in the 70's that deduced exactly the same thing. The state of traffic "science" seems to be about repeating the same insight over, and over, and over ...

dark helmet (4, Funny)

twoboxen (1111241) | more than 6 years ago | (#22635588)

I knew it... I'm surrounded by *ssholes.

Keep braking, *ssholes!

The solution is to speed up (1)

blueZ3 (744446) | more than 6 years ago | (#22636102)

You can get away from the *ssholes by speeding up until you go to plaid

Old news? (0)

Anonymous Coward | more than 6 years ago | (#22635592)

Hasn't this been known for a long time? There was even an article on here a few months ago where researchers found a mathematical model that came to the exact same conclusion. Even that story was tagged as "duh".

I'm not normally one to complain, but I thought that everyone knew this.

Re:Old news? (0)

Anonymous Coward | more than 6 years ago | (#22635718)

from TFA:

"The mathematical theory behind these so-called "shockwave" jams was developed more than 15 years ago using models..."

"Now a team of Japanese researchers has recreated the phenomenon on a test-track for the first time."

stability (3, Interesting)

backwardMechanic (959818) | more than 6 years ago | (#22635614)

'If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred.'

Is that true? If the robots had been fixed to a set driving speed (open loop), maybe. But if the robots had some sort of collision avoidance, it could still happen. It's instability in the control algorithm, no?

prehistoric (2, Funny)

cinnamon colbert (732724) | more than 6 years ago | (#22635624)

I can't find the reference, but clearly remember reading about the physics of traffic jams 20 years ago.
there are a lot of complex things going on, but two simple principles stand out
  when someone ahead of you brakes, you need some time (distance) to react
if you are far enough away, you will slow the same amount as the person ahead of you
if you are to close to the vehicle ahead of you, then your reaction time is such that you will over compensate and over brake; the same to the person behind you and so forth
the trnasition between these two regimes is quite sharp

second, people slow for any distraction - a bright sign, a hill, whatever....

Re:prehistoric (2, Informative)

foobsr (693224) | more than 6 years ago | (#22635772)

I can't find the reference, but clearly remember reading about the physics of traffic jams 20 years ago.

I do as well, and I recall there was even software (e.g. GPSS) to simulate the phenomenon. But nice to see how an experiment validates historic findings (which have probably not made it to Google yet and thus practically do not exist).


Re:prehistoric (1)

mikael (484) | more than 6 years ago | (#22635860)

Most researchers describe the field as Phantom Traffic Jams"> []

Re:prehistoric (0)

Anonymous Coward | more than 6 years ago | (#22636046)

This is very old news, i also tried to find a reference, but i guess that it is too old!
In the UK, on motorways, at busy periods, they lower the speed limit from 70mph to 50mph, to improve traffic flow

Research in Japan (1, Funny)

Anonymous Coward | more than 6 years ago | (#22635632)

I'm now really tempted to go to Japan. I'm pretty sure I couldn't get that experiment past human subjects review in the U.S.

I love discussing traffic jams... (2, Informative)

explosivejared (1186049) | more than 6 years ago | (#22635636)

... as much as the next guy, but it's been done here [] many times. Slow news day I guess, but nobody is surprised by this. It's pretty much common sense.

See when you put cars in the article, that immediately takes away the ability to use a car analogy. No car analogies = no lively discussion, or something like that. It's an approximation. Adding Natalie Portman or something involving Ron Paul changes the equation slightly, but car analogies are where it's at.

Re:I love discussing traffic jams... (1)

cretog8 (144589) | more than 6 years ago | (#22635730)

it's been done here many times. Slow news day I guess, but nobody is surprised by this. It's pretty much common sense.

Still worthwhile. Common sense can be good, or can be completely wrong. Math (well done) is right and provides strong theory to work with, but might not say anything about the real world if the analogies are off. Real experiments tell you what really happens. (0)

Anonymous Coward | more than 6 years ago | (#22635684) []

i guess this needs to be posted so others can read it.
i wish i could get a grant to study the obvious.

Wow, big news. (2, Interesting)

Ihlosi (895663) | more than 6 years ago | (#22635690)

So they managed to re-create a phenomenon under controlled conditions that anyone who has ever driven on a crowded highway can readily observe ? Whoop-de-doo.

Then again, I remember seeing stuff like that back at the university, where they were trying to combine traffic models with a Kalman filter to achieve better traffic jam prediction. That was, uh, over five years ago.

Re:Wow, big news. (1)

91degrees (207121) | more than 6 years ago | (#22635816)

It makes sense to do an experiment. Even if something is obvious, it isn't always true (e.g. heavy objects obviously fall faster, but actually tend to fall at the same speed). It's also good to have actual measurable data to determine the effect of any attempts to reduce the traffic jams.

Re:Wow, big news. (1)

belthize (990217) | more than 6 years ago | (#22635888)

I was thinking similar thoughts. I've seen this phenomenon discussed multiple times
over the years. I'm sure it dates back to at least the 70's and probably earlier since
it's an easily observed and understandable condition. The only thing that's 'news' is
that they came up with yet another way to demonstrate it.

    Kind of like the article a few days ago regarding the 'physicist' who had 'identified'
the fastest way to board a plane. Congrats Skippy, now go stand in line behind the
bazillion other mathematicians/physicists/random people who ever boarded a plane who
came to the exact same conclusion.


Re:Wow, big news. (1)

belthize (990217) | more than 6 years ago | (#22635942)

    Bad form replying to my own post blah blah blah ...

    Just google for 'highway slinky effect'. This paper []
discusses the phenomena and others in decent detail. It
references papers dating back to 1960 and even the '39 World's Fair.


Experiments not needed (1)

Irish-DnB (161087) | more than 6 years ago | (#22635696)

Who needs an experiment to prove this. I get stuck in jams every bloody day because of this effect

Intelligence is all it takes... (1)

PC and Sony Fanboy (1248258) | more than 6 years ago | (#22635698)

Each small fluctuation will be magnified.
What ALSO makes sense (to me) is intelligent driving! If you keep a constant rate of speed, then you're not causing problems. It is the people who don't know how to use cruise control (or insist on admiring the view, while driving in the fast lane).

It might also help if we didn't have so many transport trucks on our roads! I'm not sure if this is a problem in japan, but in north america, it is VERY difficult to keep a constant speed with transport trucks (grumble grumble).

... The other side of this problem, is the ROAD design! If the roads were designed properly, we wouldn't have people making waves at every turn!

Re:Intelligence is all it takes... (0)

Anonymous Coward | more than 6 years ago | (#22636110)

If people didn't mind paying the HIGH COST for designing and building GOOD QUALITY ROADS and didn't mind ROAD CONSTRUCTION we wouldn't be having this problem. But people don't pay directly for roads (at least not toll roads) so they don't see the true costs.

It's all the aggressive drivers... (2, Insightful)

NetDanzr (619387) | more than 6 years ago | (#22635700)

...that cut people off, forcing them to brake. What makes this even worse here in Atlanta is the fact that nobody uses blinkers to indicate they are about to cut you off. I propose a system where cars of people who cut others off are immediately stalled. That'll help the traffic flow...

Its all the SLOW drivers. (2, Insightful)

PC and Sony Fanboy (1248258) | more than 6 years ago | (#22635736)

Its all the people driving SLOWLY that makes us aggressive people cut them off!

Re:Its all the SLOW drivers. (1)

splutty (43475) | more than 6 years ago | (#22636006)

Its all the people driving SLOWLY that makes us aggressive people cut them off!

Making them slow down even more, and consequentially making everyone behind them slow down even more, shockwaving to a total standstill some miles down the road.

Yeah.. So actually cutting someone off makes sure you won't have anyone behind you for a while. Hmm... There might be merit to that idea :)

Re:Its all the SLOW drivers. (1)

NetDanzr (619387) | more than 6 years ago | (#22636028)

Won't help you much, because n front of you is an aggressive driver who cuts people off, creating another traffic slowdown that you're just gonna hit in the next minute or two ;)

Re:Its all the SLOW drivers. (0)

Anonymous Coward | more than 6 years ago | (#22636024)

Its all the people driving SLOWLY that makes us aggressive people cut them off!

100% wrong.

It is the folks cutting in that cause the problems. If we could all maintain proper following distance, then we could ALL go faster and no jam would occur. These "waves" happen because folks aren't spaced far enough apart to absorb minor fluctuations in speed without braking.

The problem with driving correctly is that someone who thinks very well of themselves will see the large space in front of you and cut in.

Result? Everyone slows down.

Your aggressive driving doesn't slow you down. But the aggressive driving of the asshat a mile ahead of you sure does. (and the folks a mile behind you are suffering from your asshattery)

Re:It's all the aggressive drivers... (0)

Anonymous Coward | more than 6 years ago | (#22636020)

I agree completely! Better yet, make it a voting system.

1. Every driver gets three ballots per hour on the road to use as they see fit.
2. Any driver you feel is driving poorly may be electronically given your ballot.
3. You may vote for any driver only once during a one hour period.
4. Any driver receiving 3 ballots within a 15 minute period has their car disabled for 15 minutes.

We also need to install penalties for those who wait until the last second to exit the highway. The penalty is a graduating rate according to how far past the exit stripes they travel before they actually exit.

These are just off the top of my head. It's not like I've been sitting in traffic, seething over the stupidity, wondering if thermite can be delivered in a controlled way to a car wheel...

Did they try putting the drivers in SUVs? (0)

Anonymous Coward | more than 6 years ago | (#22635734)

Traffic jams have nothing to do with morons commuting in the left lanes and forming flying roadblocks.

Figured this out a long time ago (0)

Anonymous Coward | more than 6 years ago | (#22635742)

Make enough trips through the Chicago area and anybody should be able to figure this out. That's why I started keeping a good distance between myself and the car in front of me and tried keeping a slow constant speed instead of the speed up and brake pattern that would only make the wave worse.

Can I have a research grant please?

robots (2, Interesting)

MyDixieWrecked (548719) | more than 6 years ago | (#22635766)

If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred.

I, for one, welcome our new japanese robot driver overlords.

but seriously, I take this as a hint as to what is to come in the future for japan.

Another cause (0)

Anonymous Coward | more than 6 years ago | (#22635770)

That's all well and good, but if other cities are like Seattle, there are many more important causes that are responsible for all of my traffic jams-
Forcing people merging onto the freeway from the right to shift 2 lanes left because it turns into an HOV.
Having 4 lanes go down to 2 because the bridge was built too small.
Putting the fucking on ramp 10 meters in front of the off ramp so that the cars trying to enter and exit have to turn each other into swiss cheese.

In my opinion, it's bad road design and then 4 years of patchwork changes on top of that which causes all of my pain.

Easily explained phenomenon: (1)

Ihlosi (895663) | more than 6 years ago | (#22635778)

1. First car decelerates.
2. Due to reaction time, the second car has to decelerate at a higher rate in order to maintain a safe distance from first car.
3. Due to most drivers only looking at the car in front of them (instead of also checking whether the cars farther ahead are braking), repeat #2 for the following cars - each of them has to decelerate at a higher rate than the car in front of them (-> positive feedback, which is usually a bad thing in systems theory. At least if you want a stable system).
4. Eventually, you'll get to the point where one car has to stop. Traffic jam ensues.

Solution: Use computer to eliminate/reduce the influences in bold print above. No traffic jam.

3 Options. (0)

Anonymous Coward | more than 6 years ago | (#22635780)

Yes but most losers don't realise that Gravity will slow you down.
You have 3 options you retards.
1. Breaks
2. Gas
3. And lay your foot off either pedal.
* note your call will slow down with option 3

Chaos anyone... (1)

ibm1130 (123012) | more than 6 years ago | (#22635868)

I expect some bright spark somewhere will sooner or later come up with a chaos model that describes the phenomenon to a reasonable approximation. Whether or not it will have any practical benefits in my lifetime is another question entirely.

it's mindboggling (1)

Trailer Trash (60756) | more than 6 years ago | (#22635878)

how many times people keep "discovering" the same thing. This has been on /. at least twice in the past.

Everything you need to know: []

More: []

People need to do a simple google search before starting research.

30 kmph? (0)

multipartmixed (163409) | more than 6 years ago | (#22635882)

> Drivers were asked to travel at 30 kmph

Man, they drive fast in Japan!!

In the US, I have seen freeways posted with speeds as low as 55 mph! That's 545 times slower!

Leading cause of traffic jams? (1)

iminplaya (723125) | more than 6 years ago | (#22635884)

Tailgaters!! Not slow drivers, not left lane hogs, not people slamming on the brakes.

speed limits prevent these... unproved. (1)

leuk_he (194174) | more than 6 years ago | (#22635896)

"One strategy already in use to reduce shockwaves is imposing temporary speed limits, a method TRL introduced on London's M25 orbital motorway."

Here in the Netherlands 90% of all the highways have traffic detection and automated speed limits. However this does not prevent the shockwaves and is not proved by any data. People just repeat this over and over, but little actual research is done, and most research that is done is putting some traffic rules in effect and look at the behaviour of the road.

The lights minimizing the speed limit work however excellent for head-tail collisions, since everyone knows that as soon as the "50" above the highway is flashing a traffic jam is forming ahead of them. This is a self forfilling proficy, since the "50" above the road is below the optimal speed of 80 where the capacity of the road is maximal. (Again a number that is not supported by research data)

And the last is the problem of non-engineers setting these limits. If you tell that 80(km/hour) is the optimal road capacity, this means that you have to set a speed limit ABOVE 80, and probably 100 or so, or else the average would not be reached.

Re:speed limits prevent these... unproved. (1)

Twisted Willie (1035374) | more than 6 years ago | (#22636140)

Here in the Netherlands 90% of all the highways have traffic detection and automated speed limits. However this does not prevent the shockwaves and is not proved by any data

It's hard to get that data, because nobody bothers keeping those automated speed limits. I've tried to follow those automated limits, but people just passed me left and right, looking at me like I was the one causing the traffic jam.

Ren Potts research in early 1970s showed the same (1)

Swordfish (86310) | more than 6 years ago | (#22635900)

Every few years, someone does research to show exactly this same result. My applied math lecturer Prof. Ren Potts gave us a whole term of lectures on the subject of traffic behaviour in the early 1970s at Adelaide Uni. He wrote a book about it, which was the course textbook. In particular, he based the theory (involving Laplace transforms) on experiments in a tunnel between New Jersey and New York. He drove a car in the tunnel and put on the brakes, and the traffic came to a halt. But then he advised that there should be traffic-slowing vehicles in the traffic stream to prevent excessive speed, and as a result, the traffic did not get the wave effect which stops the traffic totally. This just goes to show how important it is to do a literature search before doing "new" research!

Research I wish someone would do... (1)

WormholeFiend (674934) | more than 6 years ago | (#22635908) how to prevent rubbernecking.

It cause jams in BOTH directions.

Open source drivers! (1)

tedhiltonhead (654502) | more than 6 years ago | (#22635910)

If the drivers were open source instead of provided from the vendor as "black boxes" with just a wrapper interface, we could *fix* this instead of waiting for new ones to evolve...

Speed of light trumps wave speed (4, Interesting)

starglider29a (719559) | more than 6 years ago | (#22635912)

I have long thought that if there was a pair of LED's in the upper left corner of the vehicle, that indicated "at/above speed limit" or "below speed limit" this would solve many problems. The problem is that, like sound in gas, the notification to slow down is given by the car in front of you only (the molecule about to bump you).

But I could see a half a mile of cars all with little green lights, I could see (at the speed of light) the wave of yellow lights approaching and ease off the gas. The wave would be absorbed by this 'viscosity'. Traffic would flow near the speed limit or average flow rate, whichever the LED's were keyed to.

And don't even get me started on those GPS nav screens. Don't show me were I am. Show me where everyone else is. Let me see the compression 2 miles ahead and I'll chill (heh heh kinetic gas pun).

Tolls can do the same thing as well as other choke (1)

Joe The Dragon (967727) | more than 6 years ago | (#22635928)

Tolls can do the same thing as well as other choke point on roads. You can fix part of the toll part by going to ETC but to fix the points you need to add more lanes and or make merging point have more room to work at the traffic in to the main line of the road I'm looking at you I-90 / I-190 / I-294 going inbound on I-90. AUX lanes also help when you have ramps that are right next to each other.

"Those who forget the past", etc, etc, etc (3, Interesting)

Ancient_Hacker (751168) | more than 6 years ago | (#22635940)

Very silly article. IIRC traffic researchers in the mid 60's figured out the same thing, by running simulations on a 0.22 MIPS IBM/360. In FORTRAN.

Guys, there really is a benefit to hitting the library and thumbing through back issues of ld technical journals.

Modern Marvels (3, Interesting)

Ranger (1783) | more than 6 years ago | (#22635944)

I saw a History Channel Modern Marvels episode in highway tech and one researcher was using computer models and he determined it only takes one car to fuck things up for the rest of us. Let me repeat that it only takes one car driving slower than the rest of us to cause congestion and traffic jams on the highway.

Robot driving question (0)

Anonymous Coward | more than 6 years ago | (#22635958)

Why don't they build cars with a radar on the front which automatically decelerates a car to avoid collisions and maintain a safe distance? It seems like it would be relatively easy to do. I'm not talking about automated steering. Just a controller which cuts the acceleration and engages the brake if it detects that unless these actions are taken a collision will occur. Ie, kid runs out in front of the car, it brakes automatically far faster than a human could react. Or, you pull forward when at a stop light behind another car, and the other car brakes suddenly, your car also brakes instantly to compensate even though you're still pushing the gas pedal because you're looking at the radio or reacting too slow to avoid the collision yourself.

I can't think of any situations where you wouldn't want the car to do this automatically. It could also be used when parking. Why beep when you're baking into something when you could just stop the car? I guess you might need a switch or something to turn it off when you need to give someone a push or something. But that should be allowed to engage only at safely low speeds.

not quite ready to be sheeples/robots yet? (0)

Anonymous Coward | more than 6 years ago | (#22635962)

you have the 'right' to drive poorly, & don't forget, to remain silent. let yOUR conscience be yOUR guide. you can be more helpful than you might have imagined. there are still some choices. if they do not suit you, consider the likely results of continuing to follow the corepirate nazi hypenosys story LIEn, whereas anything of relevance is replaced almost instantly with pr ?firm? scriptdead mindphuking propaganda or 'celebrity' trivia 'foam'. meanwhile; don't forget to get a little more oxygen on yOUR brain, & look up in the sky from time to time, starting early in the day. there's lots going on up there.;_ylt=A0WTcVgednZHP2gB9wms0NUE [];_ylt=A9G_RngbRIVHsYAAfCas0NUE [] []

is it time to get real yet? A LOT of energy is being squandered in attempts to keep US in the dark. in the end (give or take a few 1000 years), the creators will prevail (world without end, etc...), as it has always been. the process of gaining yOUR release from the current hostage situation may not be what you might think it is. butt of course, most of US don't know, or care what a precarious/fatal situation we're in. for example; the insidious attempts by the felonious corepirate nazi execrable to block the suns' light, interfering with a requirement (sunlight) for us to stay healthy/alive. it's likely not good for yOUR health/memories 'else they'd be bragging about it? we're intending for the whoreabully deceptive (they'll do ANYTHING for a bit more monIE/power) felons to give up/fail even further, in attempting to control the 'weather', as well as a # of other things/events. []

dictator style micro management has never worked (for very long). it's an illness. tie that with life0cidal aggression & softwar gangster style bullying, & what do we have? a greed/fear/ego based recipe for disaster. meanwhile, you can help to stop the bleeding (loss of life & limb); []

the bleeding must be stopped before any healing can begin. jailing a couple of corepirate nazi hired goons would send a clear message to the rest of the world from US. any truthful look at the 'scorecard' would reveal that we are a society in decline/deep doo-doo, despite all of the scriptdead pr ?firm? generated drum beating & flag waving propaganda that we are constantly bombarded with. is it time to get real yet? please consider carefully ALL of yOUR other 'options'. the creators will prevail. as it has always been.

corepirate nazi execrable costs outweigh benefits
(Score:-)mynuts won, the king is a fink)
by ourselves on everyday 24/7

as there are no benefits, just more&more death/debt & disruption. fortunately there's an 'army' of light bringers, coming yOUR way. the little ones/innocents must/will be protected. after the big flash, ALL of yOUR imaginary 'borders' may blur a bit? for each of the creators' innocents harmed in any way, there is a debt that must/will be repaid by you/us, as the perpetrators/minions of unprecedented evile, will not be available. 'vote' with (what's left in) yOUR wallet, & by your behaviors. help bring an end to unprecedented evile's manifestation through yOUR owned felonious corepirate nazi glowbull warmongering execrable. some of US should consider ourselves somewhat fortunate to be among those scheduled to survive after the big flash/implementation of the creators' wwwildly popular planet/population rescue initiative/mandate. it's right in the manual, 'world without end', etc.... as we all ?know?, change is inevitable, & denying/ignoring gravity, logic, morality, etc..., is only possible, on a temporary basis. concern about the course of events that will occur should the life0cidal execrable fail to be intervened upon is in order. 'do not be dismayed' (also from the manual). however, it's ok/recommended, to not attempt to live under/accept, fauxking nazi felon greed/fear/ego based pr ?firm? scriptdead mindphuking hypenosys.

consult with/trust in yOUR creators. providing more than enough of everything for everyone (without any distracting/spiritdead personal gain motives), whilst badtolling unprecedented evile, using an unlimited supply of newclear power, since/until forever. see you there?

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all is not lost/forgotten/forgiven

(yOUR elected) president al gore (deciding not to wait for the much anticipated 'lonesome al answers yOUR questions' interview here on /.) continues to attempt to shed some light on yOUR foibles. talk about reverse polarity; []

Ok, now ask yourself... (1)

starglider29a (719559) | more than 6 years ago | (#22635968)

We have these cars that automagically follow the car ahead at the same distance. What happens if you put a chain of them on the freeway?

*scoff* (1)

to_kallon (778547) | more than 6 years ago | (#22635972)

caused when one driver brakes

a good driver doesn't need brakes.

They needed research to know this? (0)

Anonymous Coward | more than 6 years ago | (#22636022)

WTF happened to common sense? Fluid dynamics seems to cover this quite well.

Duh (1)

dreamchaser (49529) | more than 6 years ago | (#22636038)

Am I the only one who said 'Duh' when I read this? I've known this for many years. It took a STUDY to figure it out?

A series of events (1)

downix (84795) | more than 6 years ago | (#22636050)

90% of traffic jam's issue stem from everyone trying to rush. They go faster than the speed limit, but then encounter someone actually going the speed limit, so put on their brakes, or they cut in traffic, again, needing to use brakes. This cascades backwards rapidly.

If people just stuck to the speed limit, used their signals properly, and did not rush around like piglets at feeding time, a lot of traffic jams would be nonexistant. It's just being courteous to your fellow driver.

I wonder... (1)

OrochimaruVoldemort (1248060) | more than 6 years ago | (#22636056)

should this go on mythbusters? it would be nice if they explained it, or if something went horribly wrong, it would look cool

Waste of gas (1)

Zerth (26112) | more than 6 years ago | (#22636064)

I don't see why they needed to actually go driving. It is easy enough to see that anything with accumulating fluctuations that are positive-limited(i.e., you can't go faster than the guy in front of you) will eventually end up in such a state. Driving, line manufacturing, network traffic, etc.

Just take a number of 6 sided dice(or whatever polyhedra you have handy) and have them represent each car and the varying distance driven per turn. Each should average 3.5 in the long run; however, each die cannot go faster than the one "ahead" of it. So if one rolls higher than the one in front, it gets capped and so does every one behind it.

Despite the dice averaging 3.5 individually, the last die's average will drop like a rock. If you have enough dice, the line will even develop the waves one sees in rush hour traffic.

I found their comment about robot drivers particularly funny, since the same thing happens in roboticized production lines. Even with robots, there is a tiny variance in the time it takes to produce a unit of work and I've seen it happen after several days of continual operation.
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