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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.'"
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.
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.
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.
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.
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 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 always kinda fantasized about a switch that did the following:
-Activate the brake lights
-Activate a set of hydraulics to boost the read of the car up an inch or two
-Release a little smoke from a point near the rear wheelwells
-Play a loud screeching sound from a loudspeaker mounted under the trunk
Simulated emergency stop! Should give those tailgaters a reason to back off...
=Smidge=
I played with this a couple of years back:
:-(
http://vwisb7.vkw.tu-dresden.de/~treiber/MicroApplet/
shame this post is buried down deep