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Experiment Shows Traffic 'Shock Waves' Cause Jams
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.'"
If someone breaks their car I'm sure it could cause traffic to stop moving...:-P
You can tell I'm an aries because of my ram.
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.
Non impediti ratione cogitationus.
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.
If he's the Walrus then can I be a penguin please?
Yes, and the other part of science is...
GOING INTO THE FIELD AND DOING PRACTICAL EXPERIMENTS.
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.
Non impediti ratione cogitationus.
...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...
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.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
Its all the people driving SLOWLY that makes us aggressive people cut them off!
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.
//TODO: Insert catchy phrase
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.
The louder he talked of his honour, the faster we counted our spoons. -- Ralph Waldo Emerson
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.
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>
-mcgrew
mcgrew's razor: Never attribute to stupidity that which can be explained by greedy self-interest
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.
http://en.wikipedia.org/wiki/Control_theory
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.
Bavarian Purity Law of Rice Krispie Squares: Rice Krispies, Marshmallows, Butter, Vanilla.
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.
;)
In response: you can't always speed up, since sometimes the guy in front is driving slow and the people in the next lane over are driving too close to move over. You being a dangerous driver is not helping anyone and I'll more likely brake to piss you off - that way we are both being dangerous
What gets me are middle lane drivers that drive at 90km/h, when the right hand lane is free, forcing everyone to over-take (ok), or under-take (not ok)
Jumpstart the tartan drive.
Perhaps I should elaborate on the economics of this mechanism (although much of this is a repeat of the journal entry that you might want to check out).
When roads suddenly cost a lot at peak times, that *creates a market* for someone to start a bus service. The bus pays a higher toll, but takes more people, so it costs less *per traveler*. The genius of the toll is that it puts a price on a scarce resource and allows for *whatever* solution is compatible with the correct price of the scarce resource. People could do a van pool, or move closer, or rearrage work hours, or more densely pack businesses when they build them so a bus line has more potential passengers.
Nobody worries about "privatizing agriculture without providing another means of food" -- once the food is correctly priced, entrepreneurs work around it.
Now, like his journal entry mentions, you could, perhaps as a transitionary measure, run a free bus service, but probably the middle class would prefer to just pay $8 (much less than an hour of labor) to ride a clean, restrictive, private bus. Moreover, it's guaranteed that they won't end up "in the same traffic again" because the plan, as stipulated, keeps raising the tolls until it accomplishes the goal of smooth traffic flow. Presumably, you agree that some toll exists high enough to do this. (People seem to pack into airplanes just fine when the price is right.)
I agree that governments mismanage money and do cash grabs, but that's not an argument against the merit of properly pricing roads. If that's an issue, divert the funds to a specified trust so the government can't touch it.
Do you now agree that the proposal has effectiveness you didn't appreciate before?
Information theory is life. The rest is just the KL divergence.
I really hope that this isn't truly a "new" discovery. If someone sits and thinks about it it should be really obvious. I have posted a basic explanation as a comment to a number of blogs and I'm not a traffic engineer.
Once traffic reaches a point of saturation ANY change is flow will bring traffic to a halt. This includes things like a road feature that makes people accelerate, a merging or diverging ramp, or a hill or corner that allows people to see farther ahead inducing them to adjust their speed.
Any change in relative speed will at some point cause a person to slow down. If they are accelerating they will slow when they get close to the car in front. If they are slowing then that is obviously a slow down. Each car behind this change reacts to it after a delay. The longer the delay the more they have to react. People tend to react much slower then they normally would because very few drivers focus primarily on driving. They only use the minimum attention that is necessary. This just makes the problem worse. It only takes a few cars for a subtle adjustment to become a complete stop. The length of time each successive car is stopped will become longer and longer.
To make the problem worse the same 1 to 2 second delay in reaction applies to the acceleration of the vehicles after the slowdown/stop. Every fraction of a second that a person delays accelerating is adding to the stacking of the delay.
To look at another aspect of a slowdown...
If you have a smooth flow of traffic at a fixed speed you will have a certain number of cars passing a point on the road per minute. If you have a slowdown you will reduce the number of cars passing per minute. But the traffic was already at a capacity flow so the number of cars feeding into this situation continues unabated. It is obvious that the flow of traffic is done until the quantity of vehicles feeding into the situation is drastically slowed to less then the flow of traffic at the restriction. (In Orange County, CA that means waiting till after 6:30PM for a situation that started at 3:00PM.)
What can be done about this without building a vastly increased number of lanes? (The I-405 is already 14 lanes in central Orange County. Increasing it to 20+ lanes would cost billions and in 20 years when they are done we would need 30+ lanes...)
A big improvement could be made through driver training (Yeah right...). Teaching people how to merge can reduce the constant forced slowdown from cars merging onto a freeway at less then freeway speed. The correct speed to merge at is 5 to 10 MPH FASTER then the flow of traffic. A car won't accelerate quickly but it will slowdown quickly so you simply drive down the on ramp picking the hole in traffic you will merge into and brake into that hole matching speeds. This minimizes the disruption. "Freeway Meters" on an onramp actually make this problem worse on a freeway that is still flowing at a reasonable speed because they reduce the distance that a car has to accelerate insuring that they enter the roadway at a reduced speed causing traffic to slow down for them.
Teaching people to slowdown after they are on an offramp will also help reduce the disruption to traffic flow. Most drivers slow down a minimum of 10mph before the exit the roadway causing large backups for open free flowing offramps.
To reduce the effect of slowdowns you can teach people to look past the car in front of them and try to slowdown before the car in front of them, which can reduce the quantity of speed they have to scrub off. If they look ahead and start to accelerate earlier this will cause a similar improvement in reduction of traffic impediment.
(Truth is that you will never be able to teach people to change their driving habits because their cell phone, their coffee, and their daydreams are way more important then driving the 1-1/2 tons of steel they are sitting in.)
somebody said:
> 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
You have a logic failure:
1. If the 'speed limit' is 65 and the flow of traffic is about 55 then everybody's lights would be "red" and there would be no wave visible. Existing brake lights provide an approximation that is more direct than your suggestion.
2. You assume that people actually look this far ahead and think while driving. Many many folks just watch the car directly in front of them. No "solution" that depends on changing the non-forced behavior of the drivers will work. (An example of a forced solution would be the access ramp lights that make people stop before getting on the freeway -- people hate them and would never do that voluntarily even though they work).
We need to invent cars that drive themselves and then the driver can watch a movie and let the robotic algorithms take over the world.
Moral of the story: If you're afraid of driving, don't!
I like the 3 second rule better than the car length rule. Regardless of your speed you should be 2-3 seconds behind the next car.
And yes. Tailgating certainly is a HUGE problem. What's most astonishing to me is how many people shrug it off as no big deal or even justify their own tailgating behavior by saying something like: "Well, it's much worse and more dangerous to be driving slow on the freeway." This is of course utter nonsense. Tailgating is insanely dangerous, leads to a huge number of accidents, and in my mind is the equivalent of pulling a knife on someone for taking too long getting their wallet out at the grocery store.
(I would love to see widespread police crackdowns on tailgating, but I'm guessing it's just easier to prove speeding in court so that's where the tickets go. Anyone know if that's it?)
http://nerdcartoons.com/
Well of course you're going to need your brakes. The point is using them as little as possible. If the light ahead is red, take your foot off the gas! The idiots who live here race from red light to red light. I'm always amused when some moron zooms past me as I coast along, only to pass him as he's starting from a dead stop at the now green light.
That as well as maintaining a reasonable following distance, traffic permitting.
Your post gave me visions of Frank Drebin hitting trash cans as he pulled up to a curb.
mcgrew's razor: Never attribute to stupidity that which can be explained by greedy self-interest
I'm convinced tailgating is the primary source of this problem. It's not so much that drivers want to tailgate but rather they're trying to drive at the maximum speed the conditions allow. This basically guarantees that they do tailgate and then are forced to brake on a regular basis to moderate their speed. And of course once anyone brakes it gets amplified because anyone behind them brakes even more. Aggravating this problem is the fact that many of these people are apparently incapable of coasting, and instead stomp on the gas every time they see an opening.
I've read, and have observed for myself, that big trucks act as dampers. Because they brake and accelerate more slowly they need to maintain greater distance from vehicles in front of them. They can nullify a traffic wave because by the time they've reached cars which had been stopped they've begun moving again which essentially ensures that the truck continues rolling.
I've applied this technique to rush hour traffic myself and unless traffic is particularly bad its extremely effective. Basically accelerate more slowly than the car ahead of me giving myself a considerable gap. And by considerably I mean a good 5 to 10 car gap. Then I let myself roll in first, maybe second gear. If I see cars braking ahead I regulate my speed more carefully. Most of the time, when I reach those cars ahead of me they're already accelerating again and I keep right on moving, maintaining a consistent speed.
What disrupts this is when idiots feel the need to get into any opening they see, worse, when they can't stand the fact that I've left an opening in front of me larger than they find acceptable. To them, they're not making progress if they aren't riding someone else's bumper.
I usually find that in rush hour this doesn't happen as frequently because people seem to be worn down an resigned to slow-moving traffic. They jockey for position a lot less frequently than they would on the weekend when heavy traffic is less common.
Then there's the New York area where drivers are overly aggressive and downright idiotic. There's nothing to be done then. But I also think their driving habits have arisen as a result of horrendously designed and constructed highways. I think better highway design could go a long way to alleviating traffic problems.
Depends on the design of the on and off ramps. Those off ramps that force you to slow down to 40km/h (25mph) about 15 meters after the off ramp stops... practically forcing you to slow beforehand. :(
Oh, and some locations have the cute idea to have an offramp and an on ramp in the same location, using the same stretch of road. Meaning you get on the freeway, and if you continue going straight you end up going off the freeway. This results in traffic trying to get on the road having to work around traffic trying to work around those that want on the road.
Design roads better!
Right. In the area I'm in, I see that kind of behavior all the time. And you're right that it's a mentality and habit that follows the driver everywhere. I've had people tailgating me through 20mph school zones. For that matter, I've had people tailgate me in parking lots.
Another interesting aspect of the problem is how many people who aren't these kind of habitual tailgaters will become tailgaters when speeds drop, e.g., on exit ramps. They maintain a safe distance until the speed gets down to 50 or 40mph. Then it's as if they forget that much past 30mph is fatal crash territory, and they plant themselves one foot off the next car.
I think the root cause for all this is a lack of respect for how potentially dangerous driving is in general. You won't find large numbers of gun owners who play with guns like toys (though they're out there), but you can find plenty of people who treat driving with all the care and attention they put into watching TV. There just isn't enough respect for driving. If there were, accident rates would plummet. I'm just going to hold out hope for a day when reckless driving is rare.
http://nerdcartoons.com/
Your self righteous attitude is the cause of hundreds of lost hours of time for people all over the world. Instead of trying to be a one-sided-Buddha, teaching everyone patience, why not express some compassion and move over for faster moving traffic. Plus, if you are as patient as you wish other people to be you won't mind hopping into the slow lane for a few seconds.
Of course if you are motivated by some other less honorable sentiments you will continue to act as you do and feel justified and prideful about it.
Also, be aware that there are varying circumstances that may cause someone to drive faster than you. Your statement that it is because of some dissolusioned consumer fantasy belies your presupposition that the people who drive faster than you are somehow inferior to you. Believing a lie and then becoming irrationally angry with you because you show them the truth of the world makes an easy straw man to flatten. However, consider that you might be stopping someone from reaching an important destination in an appointed time. Like the time my father was in the hospital. His respiratory doctor called me and said he was not breathing without assistance and that I had very little time to get there to see him before the DNR orders took effect. I was across town at work and had no idea if I was going to get to see my father alive ever again. I cannot tell you how frustrating it was to deal with people *just* *like* *you* as I made my way to see if my father was still alive, to talk to me one last time.
But hey, one thing I have learned is that people act as they feel they must. Compelled is a good word. People who drive faster than me, I move over for them. People who drive slower than me, I just wait till I can pass them. Understanding that they have their own internal motivations that I probably do not understand makes it easier to live and let live. When I catch myself assigning characteristics, thoughts, and motivations to people driving near me I just take a deep breath and realize that I don't know why they are doing what they are doing and it is best to work cooperatively with people, even if I have never met them.
When the only tool you have is a claw hammer every problem starts to look like the back of someone's skull.
If you're in the left lane and overtaking traffic in the right lane, you're fine in my book.
If you're in the left lane, and just keeping pace with traffic in the right lane, and there is somebody behind you, you should try to move over for them when safe to do so.
It is just courtesy. I have all the patience in the world for somebody who passes somebody else slower than I might. I get really annoyed when two cars drive in side-by-side formation for 5 miles. As long as you're passing I don't care what your absolute speed is.
I agree with you somewhat, but there is another point of view on the merging problem, especially in heavy bumper-to-bumper traffic.
.02
Merging sooner increases the load in the merged-to lane and effectively lengthens its backup. And it wastes the available space in the merged-from lane. It also causes fluctuations in the merged-from lane as people speed up and slow down to accommodate the fluctuating availability of space. It's more efficient to use the "zipper" technique where *everyone* goes to the end of the merge lane and then zippers in to the lane alternately with those already in the lane. This makes it predictable for everyone involved. Those receiving the new cars know when to allow space and those merging in know they won't get stuck waiting for a gap.
But it only takes one idiot stopping early in the merge lane and forcing their way in to cause a large open space in front of them. Then the people behind him are looking at a large open space, accelerate into it. They effectively pass a bunch of people in the merged-to lane pissing them off by zooming by on the right and the whole thing falls apart.
man, I feel like mold.
It's 1 car length for every 10 mph over the speed limit. Jackass.
You bring up an issue that connects with fuel consumption and safety on the road.
It is pretty rare that anyone truly questions the vehicles that we buy today. People have accepted SUVs as the norm for driving around in the US for some reason. People will recite a number of reasons but in reality the only real reason is that they have become accepted as normal and 'cool'. It is just a change in peoples perception. If you had asked someone in the 1970s to select a 'people hauler' they would select a station wagon. It is lower to the ground making it safer to drive and is a much better layout for a vehicle. No one would have accepted a 70s Suburban, Blazer, or Bronco (even with a more luxurious interior) because of the perception, "That's a truck!"
This change of perception is actively damaging our country. Moving the increased mass of these vehicles around just plain costs energy and increases wear and tear on our roadways. If you are conscious of this and want to get a reduced mass commuter vehicle you are taking your life in your hands because of the battering ram reality of a large percentage of the vehicles.
It is really time that we do something realistic about the mass of the vehicles on our roads. A general switch to smaller lightweight vehicles would massively reduce fuel expenditures, pollution, and the smaller size would help to reduce congestion. The solution to this is to change public perception, which will probably only come about by economic reasons. The price of gas will do part of it but taxing vehicles by weight will go a long way towards making it a more equitable situation. The lighter vehicles would be rewarded for their lessened impact on the roadway and the environment. More massive vehicles would pay for increased impact on the environment, wear to the roadway, and the increased risk they pose to lighter vehicles.
People talk about rail/mass transit as a solution to LA's transportation problems but usually it is people who haven't been here. This area is so spread out in all directions that it would take an indescribable quantity of money to build such a system. The land is insanely expensive and with the sprawling area you could spend a few years of our whole nation's federal budget to build such a system. It just won't work.
(That guy who stole the tank down in San Diego about 5 years ago is starting to look saner and saner...)
BTW - From trips to Europe: I love the mass transit! Munich has a rail, subway, tram, and bus system that is so good it is just fun to use it! For 15 euro you get a pass good for unlimited use of all of the above for a week! It is just amazingly convenient and cool.
If you'll re-read the post you're responding to, you'll see he didn't care about the "casual speeder." He was criticising the maniacs who drive as much as 50% over the speed limit. Not to be insensitive, but if you were driving like that, you're doing exactly what he was criticising and risking others' lives in the process. If you were driving responsibly (although not legally) in your haste to get to the hospital, chill out. He doesn't care. Nor do I or most other people.
Even ambulances with sirens and lights operating don't drive that fast, because the risk of seriously hurting or killing someone else is too great compared to the benefit gained from time saved.
Even ambulances with sirens and lights operating don't drive that fast, because the risk of seriously hurting or killing someone else is too great compared to the benefit gained from time saved. No, ambulances with lights and sirens don't drive that fast because they recognize that they're driving very slow heavy diesel trucks not meant to accelerate, brake, OR handle, and that most of their time savings therefore come from safely negotiating intersections without stopping and waiting in traffic. If they have to spend a long time on the highway there is a problem anyway, as their base is too far from the people they need to serve.
Ambulance drivers are smart enough to realize it's unsafe to drive an AMBULANCE as fast as a car, or even most of the SUVs that soccer moms are ignorantly piloting.
And, sorry to pull out the autobahn again, but seriously, the speed itself isn't that unsafe. I'm not saying I should be able to drive 120mph thru traffic in the US because I realize myself and my roadgoing counterparts are not as well trained, and people simply aren't expecting to see that here.
But it's simply unintelligent to say that you can't drive quickly with reasonable safety.
I'm sorry, but I think the OP can figure out whether a
Criticize people for causing accidents. Give them fines, even jail time if they were truly being reckless. But don't tell me my speed alone makes me 20x as likely to be in an accident.