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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 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?
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.
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.
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.
...spike
Ewwwwww, coconut...
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.)
It's not wasting time, I'm educating myself.
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).
Guys, there really is a benefit to hitting the library and thumbing through back issues of ld technical journals.
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.
"You'll get nothing, and you'll like it!"
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.
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 ...
Dog is my co-pilot.
When traffic gets slow, I love getting behind a semi. I might not get up to speed as quickly once I'm past the problem area but I can maintain close to the same slow speed for a long time. It makes the situation much less stressful.
Yes and no.
I remember getting this as a result from a simple discrete model written in Turbo Pascal as far back as early 90-es. No need to make volunteers drive cars. Once the traffic exceeds a certain density waves and fluctuations in it will show up straight away. There is even some math proof of the instabilities in mass service theory. It's been a while so I cannot remember.
Anyway, this is Japanese science. Anyone who has had to suffer from reading a Japanese publication knows what I am talking about. Phenomenal engineering, insane experimental precision and with all due respect lousy science (unless it is done by an imported foreign devil).
Baker's Law: Misery no longer loves company. Nowadays it insists on it
http://www.sigsegv.cx/
Maybe not, but there's something your highway authority can do about it: Adopt German rules. Passing on the right gets you a ticket; driving on the left without passing gets you a ticket.
Flipping someone off gets you a ticket too, but that's another issue.
rj
I played with this a couple of years back:
:-(
http://vwisb7.vkw.tu-dresden.de/~treiber/MicroApplet/
shame this post is buried down deep
Sadly, automated traffic lights train people not to do this. If traffic is flowing with a lesser interval, the first time an interval of that size passes over the sensor, it triggers a light change. Result: the car leaving the large gap just makes it through the light, and everyone behind him gets screwed.
Therefore, drivers that have learned this by observation make every effort NOT to be behind the guy leaving a gap.
"Oh my God. This is terrible. This is the end of my Presidency. I'm fucked."; ~ Donald J. Trump
passing on the right is only illegal in certain states. I know it's legal in my state but ticket worthy in some of the neighboring states.
as for why people go all the way to the left when they get on the high way. it's just a zombie driver mentality thing. They _THINK_ they're a "fast driver" and that lane is for them, or they think that by being in that lane they're allowed to go faster.
Some drivers just go one speed no matter what road they're on. For example: last year I needed to follow my aunt somewhere, she warned me that she was a "fast driver" and that I should do my best to keep up. On the back 30MPH roads she barreled down at about 50MPH and tail gated any slower moving traffic we encountered, we got to the highway... and she still drove at about 50MPH in the left lane holding up all the traffic behind her.
In NH we have some other problem drivers too, we have long stretches of single lane highways with lots of passing zones. but all too often people are too chicken sh*t to pass and just slow down when they encounter slow moving traffic. What ends up happening is you'll get 2 or 3 of these people stacked up and now there are too many cars to safely pass with average on coming traffic. On more than one occasion I've passed 12+ cars in one shot that were putting along at 35MPH behind a tractor or dump truck in a 55MPH zone, though unless there is no on coming traffic at all it can be a rather dangerous maneuver. Completely avoidable if the slow vehicle would just pull over, or other drivers would grow a pair and pass. I know lots of people who claim they never pass because they're afraid to pull into the oncoming traffic lane even when it's completely clear.
Collector's Edition
It's not. This guy was an amateur looking at the problem a decade ago.
I've talked with the local head government transportation guy, and he said the term that they called this phenominon is the "accordian effect".
I think main motorways should be allowed to use the shoulders when traffic is backed up (w/o rumble strips). But you can get in some legal trouble if you do that today.
I also just think that cars don't scale well, and we just need a better way to get from point A to B.
I was taking compressible fluid dynamics (that's the study of supersonic flow) when I picked up a book about traffic engineering. I noticed one of the formulas was very similar to a formula I was using lots in class. I looked more closely and realized that both equations must be describing similar phenomena. I've driven hundreds of thousands of miles since then, much of it in heavy traffic. A typical problem you solve in compressible fluids goes like this: there is air flowing in a pipe at over M=1 and there is a constriction in the flow. What is the velocity and pressure after the shock wave. It's a lot like traffic is moving at high speed and high density down a 4 lane highway and one lane is closed for repair.
Of course the analogy breaks down because... well it isn't the same phenomena. Each molecule of traffic has an emotional person controlling it.
Some of my observations:
When traffic reaches what I call critical flow (a combination of high density and high speed) then it doesn't take much disturbance at all to cause shocks (a shock being a rapid decrease in speed combined with an increase in traffic density, they are characterized by lots of brake lights.) When traffic is at critical flow, cause and effect can have a very non-linear relationship. Even a polite lane change, or a pothole might tip the traffic from critical to supercritical (traffic jam.) Sometimes shocks are standing shocks. This tends to happen approaching a constriction in the road when traffic sufficiently far back is sub critical. Sometimes shocks propagate backwards through traffic like waves at the beach. An excellent example of this is 880 Southbound approaching the turnoff to the San Mateo Bridge around commute time. This one is interesting because there is drag introduced by people exiting 880 but the main disturbance comes, I believe, from cars in the carpool lane cutting across all the lanes to exit to the San Mateo Bridge. As anyone who has driven this stretch of freeway can tell you, traffic blasts along at 70 then everyone is standing on their brakes, then 70, then brakes, then 70, then...
That was the best of my macro-traffic observations, here is one funny micro traffic observation. I call it the "sticky effect" or the "stupid effect" depending on my mood. If one car is overtaking another car but only going slightly faster the slower car will speed up at least temporarily to match speeds. If the passing car is going sufficiently faster then it won't happen. Two cars on a two lane road will frequently end up right next to each other as a result of the sticky effect. Causing a "moron roadblock," which is just a line of cars going too slow blocking every lane. I also call it a rolling roadblock, and when I lived in Utah I called it a mormon roadblock.
Drive safe!
-- QED
I think the real problem of tailgating is that it becomes an ingrained habit, and the drivers who do it tailgate in all circumstances on all roads. Yesterday I was driving at 65 MPH in the right-most lane. Traffic was not particularly congested. To my left was a big rig, some hundred yards back but moving faster than I was. In the left-most lane were a few cars passing by at about 80. So a car appears further back in the right lane doing 90 or so. He didn't want to slow down the time it would take for the 80 MPH cars to get far enough ahead of the big rig to change lanes safely, so he decided to shift two lanes over to the right lane, pass the big rig on the right, and then change two lanes again to get in front of the other cars in the left lane. However, just as he changed lanes, the road graded downward and the big rig picked up speed, so by the time the speedy guy got up on the right of the big rig the gap between the rear of my car and the front of the big rig was too small for him to get through. So he angrily rode right on my rear bumper, so close I couldn't see his headlights, though even an idiot could see I had nowhere to go, since there was a car ahead of me and a big rig to my left and a Jersey barrier to my right. And I'm sure that guy thinks he was being a really good driver, and I'm sure he self-righteously complains that other people are morons who don't know how to drive.
I carry 5-6 ball bearings (steel buckshot, really, 1/4 in diameter) when I ride. They're easy to get to with gloved hands, virtually invisible to anyone behind you, simple to drop and totally non-recoverable. The effect is no different from what happens when a dump truck or tractor-trailer throws a pebble. Harmless, but effective. As for road rage, I'm not nearly as angry as I used to be -- I don't even flip the bird anymore, but I do still carry a ball peen hammer in the right side saddlebag just in case. A motorcycle can accelerate faster, corner more quickly and brake more effectively than any car. If I want to find and meet any car on the road, I can do it with ease. However, after my last roadside encounter with a motorist some ten years ago, which gained me a charge of menacing and the motorist a charge of reckless endangerment, the cop who responded gave me the advice to keep my ass in the saddle no matter how PO'd I become. He was a motorcycle cop. I've followed his advice ever since. Oh, btw, we each agreed to drop the charges we filed on each other in the end, saving lots of tax dollars and lawyer bills.
.. pa-ra-bo-la, pa-ra-bo-la, 2 pi R, 2 pi R, where's your latus rectum, where's your latus rectum, 2 pi R
I did a study back in the early '80s about traffic congestion in Los Angeles, CA and based the study on standing waves. It described how turns in the road, and other features actually contributed to the inefficiency of traffic flow. It also explained the bunching up of traffic in a wave pattern where there are actually areas mostly free of cars every few miles while other areas are packed up very tight.
This article is finding many of the same conclusions I had back then. Is there a fix? I don't know but traffic on a large scale is fluid.
God help us when we have flying cars and we have to deal with idiot drivers above us and below us!
Banjo - The more I know about Windoze, the more I love *nix
I once got pulled over in a moving van for having a broken tail light. When I explained that the moving van obviously was a rental and we were just trying to get it into the city for repairs (it had started breaking down every 20 minutes or so) _and_ that we had checked all lights before we left, he said "ok, then you were following too close" and ticketed me for that. Of course, it was bumper to bumper 5 o'clock rush hour, so everyone was following too close, but whatever.
Maybe you should visit the M42 in Birmingham, England, where a trial of allowing people to use the hard shoulder at peak times was considered a success, and it is going to be rolled out across the rest of the country.
What happens if there is a break down? You are back to three lanes of traffic, just like there would have been if you had never allowed driving on the hard shoulder in the first place. The rest of the time, you get an extra lane.
I'd guess the same thing that happens when any other lane of traffice is closed by a disabled vehicle: people will get annoyed. If you open the shoulder up to traffic it won't be like it is now with one or two morons doing 90 on it while everybody else clucks their collective tongue and waits for aforementioned morons to smack the guard rail. The new lane will receive its share of traffic plodding along at the same pace as all the others. That pace will just be a little tiny bit faster.
This already is taught, at least in the UK.
Right, I first learned about this from my GCSE Chemistry teacher in about 1986. He'd been in North Africa in the war, where supply convoys could easily be a couple of miles of a single line of traffic. Each jeep set off when it saw the one in front move, which meant that the ones at the back had to go hell-for-leather to catch up, only to realise that the ones at the front weren't going all that fast. There were regular ~100-jeep pile-ups until they instituted a system where everyone starts their engine and raises their hand when the driver in front does, then drops their hand and moves off when he does that -- which can be seen from a much greater distance along the line.
Peter