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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.'"
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.
Get your own free personal location tracker
I have respect for my fellow drivers, and only use the gas pedal. Breaking is for pussies.
Well there's your problem right there.
You wouldn't have this problem if you wrote your own drivers.
If you can read this, I forgot to post anonymously.
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...
I knew it... I'm surrounded by *ssholes.
Keep braking, *ssholes!
TODO - Insert Creative/Witty Signature
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.
'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?
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?
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!"
1998 called and wants Its amazing news back Except he even built animated Gifs to illustrate!
meh
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.)
I played with this a couple of years back:
:-(
http://vwisb7.vkw.tu-dresden.de/~treiber/MicroApplet/
shame this post is buried down deep
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.