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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.
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.
liqbase
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
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.
'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?
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....
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.
... 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.
I got a catholic block.
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.
Who needs an experiment to prove this. I get stuck in jams every bloody day because of this effect
If it's too difficult, I can't understand it !
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!
...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...
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.
Its all the people driving SLOWLY that makes us aggressive people cut them off!
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...
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.
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.
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.
how many times people keep "discovering" the same thing. This has been on /. at least twice in the past.
Everything you need to know:
http://www.eskimo.com/~billb/amateur/traffic/traffic1.html
More:
http://jalopnik.com/335832/traffic-jam-mystery-solved-++-blame-the-wave
People need to do a simple google search before starting research.
Do you have ESP?
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.
> 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!
Do daemons dream of electric sleep()?
Tailgaters!! Not slow drivers, not left lane hogs, not people slamming on the brakes.
What?
"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.
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!
...is how to prevent rubbernecking.
It cause jams in BOTH directions.
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...
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 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.
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!"
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?
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?
caused when one driver brakes
a good driver doesn't need brakes.
The only way to get rid of a temptation is to yield to it.
-Oscar Wilde
WTF happened to common sense? Fluid dynamics seems to cover this quite well.
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?
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.
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.
Karma Whoring for Fun and Profit.
should this go on mythbusters? it would be nice if they explained it, or if something went horribly wrong, it would look cool
If people can get past, can they get future? Best way to confuse a stoner
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.
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.
You can get away from the *ssholes by speeding up until you go to plaid
Interested in a Flash-based MAME front end? Visit mame.danzbb.com
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.
--- Justin Dearing http://www.justaprogrammer.net/ We're just programmers.
Traffic Waves
Vivin Suresh Paliath
http://vivin.net
I like
1998 called and wants Its amazing news back Except he even built animated Gifs to illustrate!
meh
I expected this story to be a dupe of this decade-old article by a guy who figured out the same idea.
Unpleasantries.
What rights does one loose?
I, for one , would love to see at traffic jam moving at 30,000 miles per hour!
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
The rate of braking is two or three times the rate of acceleration. This factor alone would account for the problem but there's more. People tend to brake or slow far below what any given instance requires for speed matching. And finally, the casual observer can also note that when drivers move to resume normal travel speed, they often delay their acceleration by waiting for the vehicle in front of them to have moved at least two car lengths before they start to roll from a full stop.
The short description of all this is we have a bunch of retarded slow-brained people who cannot react quickly enough.
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.
This would all be solved if the rest of you would just use public transportation so I could get to work faster.
I just saw an episode of Modern Marvels about the highway system. They showed a cool clip of some MIT students who made a traffic simulation. Projected on the wall was line outlines of a highway system and thousands of rectangles representing cars moving along. From the looks of it, it looks like a computer was simulating how those thousand cars would react to the cars around it, with some randomness thrown in of course. The thing looked like it could've been SimRoadEngineer on steroids.
With two lanes in each direction, they showed in the simulation how a single car going 30 MPH in the "slow" lane could cause a miles long traffic jam involving thousands of cars.
As an side thought, following a car with just enough room to break *is* tailgating. Staying back a couple of seconds definitely smooths the flow of traffic. Maybe just as importantly, acting predictably greatly reduces traffic accidents. I have a few friends with more sporty cars that like to tail people. Yeah, they're paying attention, and they can slow down quick, but it still causes traffic.
This phenomenon is obvious also to those who have gone through basic training. Often in marches you have the accordian effect where the front group is fine but due to small time differences in stopping and starting, that are amplified backwards, the rear unit often is running and stopping. The same occurs on the road whereby one person brakes and then many others brake before they need to. When traffic moves, people tend to start slower than needed. This is what creates these "phantom menaces" that backup traffic for no reason. Oh, that and people don't know how to merge correctly!
posting AC because some errant mods have been going through my history to mod me down long after the fact
We all get bad downmods; although at least one downmod I got a couple of days ago was understandable. The post was inaccurate even if it did make the point I was trying to make.
But I just looked at your recent comment history because of that fact; there seem to be some mods who will downmod you for no reason whatever. I've been getting a lot of posts modded "overrated" (yet still manage to garner a 5. Hmm.) But I see:
(Score:-1, Flamebait) Hi, I'm the self-important liberal who think he's saving the earth by driving a slightly-more fuel-efficient car to his giant home in suburbia.
Often it's not what you say, but how you say it. To a self-proclaimed liberal, your post IS flamebait. In the same post you did pretty much the same to conservatives, slashdotters, and everyone. I wouldn't have modded the post itself at all, but if I see it metamodding I'll likely mod the mod as "fair".
This one had one mod moderate it as "overrated" while one guy modded it back up with "underrated". In that case the "overrated" most likely came because one would have to know Japanese for the comment to make any sense.
(Score:-1, Troll) WAIT! Quick, environmentalists, rationalize how it's not good enough!
Come on, man, I did a journal about this topic a few weeks ago titled "This Journal is a Troll", but from the top few comments of yours I can see how your karma went down the flusher. Had the last one I mentioned where you bashed environmentalists left off the part I quoted it would have almost certainly been modded well.
Also, you might want to check out this list. You seem to have pissed off a LOT of people. Like I said, often it's not what you say buy how you say it.
-mcgrew
mcgrew's razor: Never attribute to stupidity that which can be explained by greedy self-interest
Stop following so closely!
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
How in the hell do you manage that???? Here in Springfield where traffic isn't nearly as bad as up there if you try to keep a 5 car length distance on the highway (you should have 6.5 car lengths, one for every 10mph) three cars will get between you and the guy in front of you!
When are we going to get idiot lights on our dashes that light up when you're too damned close? Would idiots even heed them?
mcgrew's razor: Never attribute to stupidity that which can be explained by greedy self-interest
This is why police generally don't stop people for speeding on Houston freeways. It backs up 4+ lanes of traffic for miles. People have to stop and see what the fuss is about. The only times I have seen people pulled over is for something very serious. The suspects usually have their hands on their heads and are sitting on the sidewalk.
Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
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.)
Wow, I thought this was common knowledge already, at least within traffic engineer circles. In my little world, anyway here's a report from 1994...
Graduate students and most professors are no smarter than undergrads.
They're just older.
"first experimental demonstration of a phenomenon that causes a busy freeway to inexplicably grind to a halt"
Nope, not first. Texas A&M has been studying this for over a decade. I've read several other stories from various organizations as well. But, whatever.
I just don't get what's odd, mysterious, or difficult to understand about this. Obviously, the carrying capacity of something is proportional to the speed that stuff travels along it. So if you have something that's already at capacity at a certain speed, then slow it down just a little bit, suddenly it's over capacity. We all know what happens when a road's over capacity.
The phenomenon is very similar to when a super-saturated solution precipitates. The roads really do get super-saturated, because when they're moving fast and very busy, more and more people tailgate, which really does put the road above its safe maximum throughput load. In that case, the tiniest addition to load (precipitation by dropping in another crystal, or at an on-ramp dropping in more cars) or reduction in capacity (sudden crystallization by cooling, which reduced the carrying capacity of a liquid, or slowing, which reduces the carrying capacity of a road) causes a "crystallization event."
Re: The article quote above- perhaps the mathematical models behind "shockwave" jams were only developed about 15 years ago, but I've got to thing that the "theory," - that a reduction in bandwidth on a carrier working at capacity causes a jam - must have been obvious to many people since the origin of traffic. Probably even long before then, I've seen it in person and seen videos from overhead of this happen in crowds of people walking, too. I suspect a clever person standing on a roof in Babylon watching a crowded street three thousand years ago could have had a good understanding of this phenomenon.
Can anyone tell me how to set my sig on Slashdot?
heh.
what we need is driver moderation. if somebody consistently cuts people up, brakes sharply and tail gates then other drivers will mod him. when his scores drops under a certain amount he is warned, beyond that he is banned for a week or so. beyond that the ban gets longer. maybe a financial incentive like cheaper insurance/tax for good behavior.
in other words give the driving community the means to control itself with a suitable preventative system - each driver can only mod another driver once a weeks and small lapses are ironed out.
after all, if everybody drove sensibly with a nice large gap then the odds of many of these traffic phenomena forming is reduced. clever software would give a weighting to people who's mods followed the mainstream of recommendations maybe.
Ban traffic lights. Install roundabouts. Round up and nuke those incompetents who can't learn to use them.
I run: Windows, OS X, Linux, FreeBSD. Just because you have a hammer, doesn't mean everything is a nail.
Glad the Japs finally catching on.
Criticisms of speed limits on motorways and dual carriageways is perhaps more justified than those of single carriageway limits. Although speeds over 60mph might seem safe on a single carriageway, you have to take into account that, due to traffic travelling in opposite directions, combined speed means that it is possible to have a crash at 120mph, far higher than is possible on a dual carriageway. I'm actually quite surprised that most countries have a relatively small differential between the two types of roads.
Regarding 'accuracy', I think you were getting at something different but I thought I'd point out that your car speedometer consistently over-reports your speed. There is an inherent error in the instrumentation, exacerbated by the fact that tyre pressure changes due to ambient temperature and wear. Speedometers must never under-report by law, so the differences between measured speed and actual speed can be quite large due to manufacturers being on the safe side with their calibration.
You can test this by measuring your speed using a GPS unit, or by collecting data from your car's OBD port. What I've found is that the over-reporting seems to be due to a built-in 'fiddle factor' in a vehicle rather than being factored into the actual calibration, so the speed reported by the OBD port will be higher (and more accurate) than the speed reported by the speedometer.
The upshot of all of this is that, while you might be travelling at what your speedometer tells you is 80mph and thinking to yourself, "This is perfectly safe," in actual fact you could be travelling as slowly as 75.
Definition of On-Ramp: Allows driver to speed to traffic flow to merge properly.
Reality: You're stuck behind the timid moron who would rather cause the highway traffic to brake so he can merge at the ungodly speed of 45mph.
Definition of Off-Ramp: Allows driver to exit the highway and then slow down.
Reality: The a-hole in the right lane decides to slow to 40mph and then enter the off-ramp.
I've found these are the TWO main reasons traffic bunches up on the highway.
Let's say car B is 2m behind car A, traveling down the highway. If car A slows down by 5km/h, it takes only a second and a half for car B to catch up and rear-end car A. That is not a very long time to allow people to react. If, instead, car B was traveling 20m behind car A, then car B has 15 seconds to react to a 5km/h slowdown.
You are never going to get people to keep a constant speed. Even cruise control has it's limits. Even if no one ever touched their brakes on the highway, there would still exist this kind of traffic jam because people follow to closely. Not to mention the safety concerns. Let's say that something really drastic happens and the car A slows down by half its speed. You now have a 100km car B hitting a 50km car A unless car B can hit the brakes with about a tenth of a second's notice.
I put it to you that if everyone judiciously kept 10 times more space, traffic jams would vanish.
People need to tune their mental PID controllers.
If my commute choices are driving for 45 minutes in traffic, or standing on a bus for an hour and a half with a transfer or two, I'm gonna drive.
I love public transportation, if and when it works. I'm willing to take a little longer to commute without having to drive, but I'm not willing to double my commute time in vastly less comfortable environs.
Why yes, I AM a rocket scientist!
When I find myself caught in these shockwaves, I always attempt to do my little bit of help get rid of the jam. Since the tapping on the brakes causes the deceleration shockwave, I counter that with the acceleration shockwave. Quite simply, when you begin to get through the shockwave and speed back up, KEEP ON THE GAS. Stay the (safe) same amount of distance between you and the car in front of you. If everyone in line does this, the reverse effect will be observed from the braking shockwave. However, in the real world, some Sr. citizen inevitably does not accelerate. I'll be looking in my rearview mirror and notice a 20 car length gap all of a sudden. But that gap shows that the acceleration technique should work if everyone does it. The concept is identical to starting out from a Red Light. It is unsafe, but if everyone in the line at the light started to accelerate at the same time when the light turned green, many more cars would get through. But accelerating inline with the person in front of you (and not letting those extra 3-4 car lengths build) will get everyone back up to speed much faster. I have no proof for the statements made here as I don't have 30 cars in a loop to test them out. Just my observations from the real world.
I played with this a couple of years back:
:-(
http://vwisb7.vkw.tu-dresden.de/~treiber/MicroApplet/
shame this post is buried down deep
The reason speed limits are there is to make roads safer. They are needed because people get used to and start feeling safe at any speed after driving it for a while, a phenomenom known as "speed blindness". Any particular speed limit may or may not be too fast or slow - I presume that this is what you meant by "not accurate" - but the limits in general are both neccessary and desirable.
I, for one, do not wish to die in the morning traffick because some speed freak can't be bothered to get up on time.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.
Part of a civil engineering class back in college we were comparing highway traffic to fluid dynamics. There were quite a few corrolations that could be made although if I recall pretty much every group in the class had a different conclusion on what was the biggest factor in causing traffic jams.
That's not what I've observed. Whenever anyone changes lanes, the person in front of whom the driver has merged has to slow a little to maintain a safe following distance.
I fucking hate those folks who merge at the last possible minute, especially when they have to force their way in due to congestion. If you don't have the intelligence to get in your lane a little early, you don't have the intelligence to drive a fucking dangerous vehicle. You're just contributing to the problem, idiot! It's just casual selfishness that saves very little real time, and just adds to the problem.
Anyway, I guess I'm just saying, "Me, too."
Microsoft is to software what Budweiser is to beer.
Actually, another reason for speed limits is because of the safety equipment - like crash barriers and such. If you hit a crash barrier at it's rated speed it should function properly and do what it was designed to do in the circumstances (which is to protect you), but if you hit it at twice its rated speed, then all bets are off and it is not likely to perform as designed.
Once I was a four stone apology. Now I am two separate gorillas.
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
This is an area that has been studied repeatedly multiple times apparently. My experience with it was with the Port Authority of New York and New Jersey, which I interned with back in the early 1970's. They used a simplified case - a model of the Lincoln Tunnel, which has no intermediate entry or exit points, and does not allow lane changes. But the principle is the same, even for major highways (just more complex). They had done modeling of tunnel traffic, and wanted to increase hourly throughput by 10% w/o having to build additional tunnel lanes. At say 2000 vehicles per lane per hour, 10% would mean 200 more cars / trucks / buses into the city during rush hour - a worthwhile objective.
They used a combination of two technologies - a "speed trap" in the roadway, and a stop light at the tunnel entrance. By monitoring the traffic in the tunnel, they could avoid stalls by using the traffic light to stop cars entering by just a bit. Introducing this delay at the start of the tunnel caused gaps in the traffic which allowed congestion to occur but not degrade into a stall condition. And all this was based on late 60's technology - DEC PDP-8's (at least that's what I remember).
I say all this to show just how much of this stuff has been in the works for decades, and we still need to get more done. For example, the Port Authority also was experimenting at the same with a "dinosaur" version of the kind of technology that eventually became the EZ-Pass. The idea was to mount a transponder on buses so that they wouldn't have to stop at the toll booth. Similar goal - no stops meant more buses could get through the tunnel per hour.
While it is worthwhile to continue to study all this, it would also be useful to try practical adaptation. the Port Authority was a very innovative place; they didn't just study these things (with help from academics), but they put them to use. Of course, some might view this as not relevant to today, but I think it is.
To me the best solution to "congestion" is actually variable speed limits based on traffic conditions. In periods of no congestion, the posted maximum is permitted, but when congestion exists, the speed limit could be lowered to prevent stalls. I find that on most highways, people always want to do the limit / go as fast as possible, even in heavy traffic. If speed monitors in the road-bed (variants of the same kind the Port Authority used back in the day appear to be in use just about everywhere now) could be used to adjust traffic speed by transmitting a "maximum congestion speed" to smart road signs or even in-car displays, perhaps a similar decrease in congestion stalls could be effected even on major roadways.
Some will argue with me, but I saw it work at the Lincoln Tunnel - slower speeds combined with more gaps in the traffic permitted more cars through in total (even though individual drivers had to maintain the posted speed limit). In most parts of the US or Japan, more highways are just not practical. So the question is how do we better utilize the ones we have? Smarter use of the highways during congestion periods by reducing maximum speeds could be one answer; and this means making sure that people don't race off at 75 or 80 once they clear a blockage, just to cause another one down the line. By reducing maximum congestion speed, you could allow more reaction time between drivers and allow the smaller gaps between vehicles to absorb changes in flow.
Not a traffic engineer these days (long time since my PA internship), but "bandwidth shaping" applies in both types of networks. As a final example, the Port Authority was an early user of "road reversal". In the tunnel itself, the 6 lanes of traffic could be reversed individually, so that for rush hours, you could have 4 inbound and 2 outbound in the AM and the reverse of this in the PM. But the PA went further - they took one lane of the outbound highway to the Lincoln Tunnel and reversed it for inbound "buses only use" during the morning rush-hour. You could view
Must we read of this again? And again?
Been there, done that, got the scrapes, tired of the research. Get these people off the road.
deleting the extra space after periods so i can stay relevant, yeah.
And this is why my license plate frame says "OMG NOOBS L2DRIVE"
Bill Beaty has had the same thing on his Amateur Science web site for years:
http://www.amasci.com/amateur/traffic/traffic1.html
I say it is tailgating that causes people to have to jam on the binders causing those behind to hit theirs.
Leave a two second gap between you and the car ahead. Look several cars ahead.
Hang up your fucking cell phone.
photosMy Photostream
I've observed that almost anything out of the ordinary causes a braking ripple. Any sort of flashing light (even if it's completely irrelevant to the driving situation), any debris on the side of the road, a person pulled over by the cops in the oncomming lanes 300 feet away...anything that catches attention will cause a brake ripple.
I used to drive from Boulder, Colorado west on I-70 to the mountains to work. That part of I-70 is one of the most dangerous stretches of road, not only b/c of the mountains, but b/c waves and waves of weekend warriors drive that stretch all at the same time. Friday night and Saturday morning were as bad as any traffic I've ever seen.
I tried to do like the parent said, and look way ahead in order to not have to use MY brake.
The main problem is, driving efficiently in a high-traffic situation requires (some) analytical thinking...the kind of thinking that so much of American culture discourages people from doing. Ignorant driving is a symptom of a greater problem...many Americans just don't use (or don't have) the mental tools necessary to operate at a high level in our society. I have no idea how to fix this problem.
Thank you Dave Raggett
My engineering professor did similar studies in the 1960s - he told us about them in our dynamics class circa 1983.
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.
Scientific American Frontiers did an episode that documented this back in 1999! Here is the transcript
How about making a lengthy, say 100m of traffic light? This way, the 100m of cars could see it's green light, and can get ready.
They're meant for breakdowns and emergency vehicles. You won't want people driving on shoulders especially on expressways where they think they can go 60 MPH when it's quite likely they might encounter a completely stopped car and have difficulty stopping.
paintball
Umm? Since when were speed limits in the interest of safety? People don't even test things for safety up to the speeds we drive let alone a false feeling of safety people have.
Yes, not accurate is exactly what I mean. However, I for one, do not need to be screwed over by traffic because some douche wants to drive just the speed limit which caused the last 3 miles of cars after him to slow to a crawl....causing me to be held up another 10-20 minutes. This same behavior incites road rage, and creates more traffic on the roads.
So yeah, get rid of the bottleneck of the feedback, and offer a method to increase performance (speed) and the issue will be gone. problem solved. Don't like driving 80+ on a 55mph highway? Get off the road/out of the way. Instead, we have people driving in the passing lane like that. This article highlights that pretty well as does the last time such a solution was shown. Simple example that has existed for a while is the autobahn. You ever seen traffic on it? I haven't.
obviously the right answer is charge a toll and subsidize bus/train transit directly with said toll money.
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Pure robotic driving is too faulty, not because of controlling speed, but because of steering. Let the human do the hard part, steering, and the wireless road network (WRN)control the speeds of cars, basically a step up from cruise control.
This would even out traffic patterns, increase traffic flow, decrease accidents, and be very easy to implement on the roads, and more imporantly VERY easy to retrofit into any car with cruise control (an automated steering/camera system would not).
The system would benefit early adoptors by simplifing driving like cruise control, and once a certain percentage of the traffic flow had this system the benefits would effect the whole traffic flow and road system.
It would also be a great transition to fully automated driving systems for everyone.
I've driven in both the US and in Germany on all widths of roads, and passing on the right in Germany is not necessary. You couldn't do it even if you wanted to, as drivers there are not morons and get back into the right lane when they are not passing.
Probably helps that the people coming up at 200 kph behind you are pretty intimidating.
paintball
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
- Hit the brakes in a pack and you may cause a crash. The next guy is about 6 inches off your back wheel.
- Hit the brakes and you have to spend energy getting back up to speed. It will cost you over the course of the race. The margin between placing and not is that thin. Really.
- You lose more energy to the "accoridion" effect the further back in the pack you are. This is really pronounced in "crits" (criterium races). Pack position is evertyhing.
- The higher the race category (i.e. experience level), the less braking, the less accordion (traffic jams), the fewer crashes and the faster race times. It's not just fitness, it's technique as well.
Which is why, as a newbie cyclist this year, I got yelled at (on team rides) every time I touched the brakes that wasn't absolutely necessary.If there's an accident during a low traffic time, you whiz by it.
Must be nice where you live. Here, if there is an accident, everybody slows down to take a look because you just might know the person.
Never mind the fact this is a city of 1.5M+ people!
Your advocacy is appropriate for moderate traffic, and I would add that generally more-aware drivers would lead to fewer traffic fatalities.
Unfortunately, I've noticed different driving practices in different regions. For example, Boston driving has a very aggressive POV ("I'm merging NOW") while NYC driving has a very defensive POV ("You're not getting in front of me") while LA driving is more like sitting in a parked car.
I say 'unfortunately' because proper safe driving, if applied to extreme environments, may promote unsafe situations. If you react unexpectedly to regionally expected behavior, then the surrounding locals may then react to your move unexpectedly - which can cascade into a traffic accident.
As for me, I refrain from driving in heavy traffic - too much drama. Usually, I'm the guy going the speed limit in the slow lane and, in moderate traffic, I usually apply the method you describe. My attitude is: I don't care if you pass me, just don't surprise me or anyone around me.
This is not my sig
When I was in the Army, we'd occasionally have to go on tactical marches. In general, the goal was to maintain a 5 meter spacing between you and the person in front of you while walking. If you were towards the rear of the columns, you alternately ran/stopped because of the yo-yo effect of everyone in front of you trying to maintain the magic 5 meter distance. The longer the columns, the worse the yo-yo effect. As it applies to traffic,
I used to drive a semi coast-to-coast. (early 80's) What I found interesting is the difference in traffic behavior in different cities during the rush hours. For example, Houston, TX traffic could be summed up with this Texas Two-step: "Go like hell. Stop" in 1/4 mile bursts.
Rats! Work calls...
You, in your lane, are essentially the "leader" of every car behind you. This is no truer than if you are on a one-lane road (you lead an infinite number of cars) but is also very true on two-lane road (you lead N cars, probably around 10-20 effectively). So, if you slam on your brakes, you will cause a ripple that will affect many other cars (and waste lots of gas in the process). Meanwhile, if you make an effort to "even out" the traffic ripples by leaving lots of space in front as a buffer, you could potentially create a huge gas SAVINGS by your actions.
Physical experiments have their limits too. What's practical about drivers running around in circles? Real roads have fluctuating traffic loads, blind turns, merging and diverging traffic and a host of other obstacles. The point of an experiment is controlled conditions to gain fundamental constants and other descriptors. What you might get from this experiment is better statistics on driver reaction time and a few other constants to refine you models.
When you really want to know how a road is going to perform, you take it to some kind of Monte Carlo simulation.
Friends don't help friends install M$ junk.
That wasn't a very nice thing to do on National Grammar Day.
http://slashdot.org/comments.pl?sid=474092&cid=22632342
This is exactly true in most of the NE. It simply is not possible to always keep a safe distance from the car in front of you. The moment you do someone will get over in front of you (Most often without use of a blinker) and stay there closing your gap.
I challenge anyone to try and drive this way without going insane, it does feel if you are constantly moving backwards.
Here is an anecdote from when I was in Deutschland:
Lesson: Germans respect the law much more than the Americans, so difficult to enforce laws will work here only if there's a strong effort to indoctrinate the populace.Make sure everyone's vote counts: Verified Voting
There's a particular spot of roadway where I live that is always a problem at 17:00. It involves an side street's on-ramp with a US highway's exit-ramp at the end of the added lane. You have to deal with merging traffic going into and out of the added lane. When the traffic is heavy I always time my approach to coincide with a hole in the opposing lane's traffic, thus making merging easier and quicker. I also don't tailgate the person in front of me. Works like a charm. Those assholes who floor it to get around a line of cars only to cut them off fuck it up for the rest of us. The same goes for those drivers to incompetent to accelerate in the acceleration lane and back up traffic with their braking. It almost makes me long for the day of automated vehicles that can negotiate and merge as part of a defined process without idiot users to screw it up.
Given a smoothly flowing, full capacity freeway (as in everyone's going at 70mph and there's a max of 3-car spacing)... I've always wondered how it's possible for a slowdown "shockwave" to ripple back and cause traffic to come to a complete stop. I mean, if the traffic in front doesn't stop, why should the traffic at the back do?! Does anyone know?
For example, why is it when we're all sitting at a red light that we don't all take our foot off the brake once the light turns green? If it is a simple issue like seeing the light, then how about we place several lights further back? Of course, people are idiots so it cannot work...but would be nice in a perfect world :D
Here is a very involved article, from 1998, that explains this "traffic wave" phenomenon. The "study" behind it was done by one guy, not by some bunch of "researchers". All they did was to conduct their experiments in a more controlled environment.
As for this being "news", that's BS. Just watch how truckers change their driving pattern when congestion starts to build up. This has been common-sense knowledge for most sensible drivers for decades. Only now there's a peer-reviewed paper about it.
-- What you do today will cost you a day of your life.
I could have told you this for a lot less money. Seriously, re-invent the wheel much?
By not following too close, I tend to look further down the road at all of the vehicles ahead of me, not just at the car directly in front of me. It is easy to see an oncoming wave of decelerating cars that is obviously out-of-sync with the traffic flow. At the wave approaches, its probable magnitude and duration as it passes me is obvious. If I happen to have a little room to play with at that moment, I always try to dampen the wave as best I can by using the space ahead of me as a buffer which I can shrink or expand to smooth out the flow. After the wave passes, I can look in my mirror and see much smoother flow behind me.
Here is another variation of what I am talking about. When in somewhat of a traffic jam, I frequently see a building wave of cars immediately ahead of me over-accelerating, followed by a wave of them suddenly having to hit their brakes and slow to a stop. Of course I use my small buffer of space to avoid joining them in over accelerating and just proceed at a speed that will use of the last of my buffer as they are starting to move again. When I look in my mirror, I can usually see a much smoother flow behind me and that the wave has dissipated.
For some reason, I rarely see any other drivers doing that. In fact most drivers movements suggest that they have no clue of what is happening just a few cars ahead of them. Perhaps, they just need to direct the focus of their eyes slightly further down the read and back off slightly from the car just ahead of them.
It does help that I sit up high enough in my pick-up truck to see what is going up ahead. Driving that way also means that I rarely ever use my brakes, in fact, the pads on my front disk brakes have never been replaced in 142,000 miles of driving. Of course, the fact that I have a manual transmission means that I get somewhat more of a braking action, just by letting up on my gas peddle. I do not think what I am doing is dangerous, since I have been driving for over 50 years without ever having had an accident.
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.
My mother always gets angry when she tries to pass somebody and they accelerate to match her speed. She thinks it's a purposeful act, done out of rudeness.
My theory is that it's a sort of herding mentality. In a group of animals, no individual wants to get too far from the group or it will be at risk of attack from predators. In a flock of birds, no individual wants to be in the lead all the time or it will tire from facing the most air resistance.
So when you're driving down the highway and you're out ahead of a pack of cars, you feel vulnerable to attack (from traffic cops) or unsafe (from poor road conditions and uncertainty of what's ahead). But if another car begins to pass you then you feel safer and unconsiously speed up. But if that car approaches and passes very rapidly then you don't have time to develop an association with them and you continue at your own rate.
This type of study is done all the time. It's nothing new. The result is completely obvious to boot.
If people slow down, people behind them will slow down.
When the front car brakes, the normal spacing of cars gets compressed due to the reaction time involved (and the fact that cars can follow more closely, and be safe, at slower speeds). Cars may even stop.
The question is "Why doesn't traffic resume to normal speed just as quickly as it slowed down?"
When someone brakes, you can see it several cars ahead. The first car brakes, and 4, 5, or more cars behind see that immediately, and act accordingly. When cars accelerate, you MUST wait for the person in front of you to accelerate before you can accelerate. Otherwise you would hit them.
This means that the delay due to reaction time in acceleration is equal to the number of cars (not counting the first car) * the average reaction speed.
The delay due to reaction time in braking is much less. It is basically equal to the number of cars (not counting the first car) * the average reaction speed, / the average number of cars you can see ahead.
And if you're talking about driving in a circle - you can see pretty damn far ahead.
Add on to that the fact the people are more likely to drive slowly after a sudden stop (expecting more such stops), and you've got yourself traffic jam 101.
The freeway meter will keep you from the car equivalent of the "packing 10 pounds of sugar in a 5 pound sack" merging problem.
The reason that the meters are still a problem is that the meters are too close to the freeway so there is no way that anything less then a drag racer can get to freeway speed before getting to the merge zone.
If it creates a guaranteed slowdown from every car that enters a flowing roadway then it has lost its purpose.
That was actually 13 years ago. My how time flies, eh?
if a temporary jam occurs, like a traffic accident, the traffic congestion will propagate backwards along the road long after the obstruction has been cleared. Sometimes you will observe gridlock on the freeway, as if people were waiting to move past a crash. Once you get to the point where the crash should be, there's nothing there and people speed away from a mass of gridlocked cars.
I read an article way back in 2003 (which I can no longer find) about how the proper way to remedy this was to convince people to keep significant space in front of their car, even when traffic is heavy. When traffic is heavy people have the instinct of moving up to just behind the car in front of them, but this doesn't actually make them go any faster, since they are moving the same speed relative to the car in front of them no matter what. In fact, it slows them and the people behind them down because if the car in front needs to slow down for a moment and there is no buffer of space between the two cars, then the car in back must also slow down for a moment. Since acceleration isn't instant, the time the car must be slowed down for increases as it moves down the line of cars.
Again, this stupid behavior disappears when people stop freaking tailgating each other, a practice which is bad for sooo many reasons.
from wikipedia
"Mathematical theories
Some traffic engineers have attempted to apply the rules of fluid dynamics to traffic flow, likening it to the flow of a fluid in a pipe. Congestion simulations and real-time observations have shown that in heavy but free flowing traffic, jams can arise spontaneously, triggered by minor events ("butterfly effects"), such as an abrupt steering maneuver by a single motorist. Traffic scientists liken such a situation to the sudden freezing of supercooled fluid.[3] However, unlike a fluid, traffic flow is often affected by signals or other events at junctions that periodically affect the smooth flow of traffic; matrix entropy models consider the effects of this by "platooning" groups of vehicles and by randomising the flow patterns within individual segments of the network."
Absolutely. I would love to see a public information campaign -- like the ones they do to get people to wear seatbelts, to not drink and drive -- that would be focussed on trying to instill some lane discipline. I even have a slogan for it:
Pass, or pull over!
My own guideline is that if I'm not going to be passing another vehicle within (say) 20 seconds, and there is a suitable gap in the nearside lane, then I will pull over. I believe that if everyone behaved like this, the throughput of the road system would be significantly greater.
ACC makes traffic flow smoother, allegedly. If 20% of the cars have ACC, there will be less traffic jams due to shock waves. It might be cost-effective for the government to subsidize such units to better utilize existing infrastructure capacity.
Stop the brainwash
Queuing theory has been around for ages. Even Robots traveling at a constant speed would not resolve the problem, since eventually, due to statistical fluctuations, there would be collisions. Robots programmed to stay a constant distance from each other would eventually start to slow down and speed up. (Again, due to statistical fluctuations.) Slowing down is more apparent in the corners (turns), but a "corner" may be as subtle as a lane change. In real life, a big contributor to the problem is that traffic tends to go slower than the speed limit, but is less likely to exceed the speed limit in order to make up for a previous slowdown fluctuation.
/. posted an article on aircraft boarding, which is a problem in the same category as traffic flow. A few years ago a friend of mine was a cameraman at a baseball "goodwill series" in Japan. He commented that there was no trash anywhere in the stadium. At the end of the game the spectators rose up and applauded the players of both teams. Then they sat down and exited the stadium row by row..and took their trash with them!
In Houston, the morning traffic is trying to diffuse into smaller capillaries such as streets and parking lots. Cross streets or cross traffic requires that the real average speed be much slower than the max posted speed. The traffic feeding into the city exceeds the capacity of the capillaries to diffuse the traffic to random destinations, and this causes backlogs that flow further "upstream" during incoming rush hour. Compressed-time photography actually verifies this effect. (There is a dynamic model somewhere, but I can't find it right now.)
Recently
I imagine a city in the future where all traffic goes in one direction, say counter-clockwise, and roads and streets use a multiple spiral instead of cross streets. Emptying the city would require that citizens "queue up" for their slot in the flow, and fuzzy logic manages the merging problem.
Imagine designing an airport where the landings and takeoffs were spaced by a program such as "Boids" ( http://www.red3d.com/cwr/boids/ ) and all the traffic followed the same counter-clockwise spiral. True, terminal design might require elevators like an aircraft carrier has, and there would be some cross-over ramps and taxiways, but an open airport could accommodate a lot of aircraft more safely and could have a two- or three-hour "reset" each night to make up for the statistical variations.
Nice article, BTW.
"The mind works quicker than you think!"
I'm talking about avoiding collisions, you know...
Kindly explain how driving at steady speed at just the speed limit causes cars behind to slow to a "crawl" ? Or did you mean that the speed limit itself is a crawling speed ?
As for road rage, it is a clear sign that the person in question is not mature enough to drie a car and should thus lose his license. Throwing temper tantrums like a little kid just because you have to wait is ridiculous.
I always drive the rightmost lane unless I have a specific reason to drive another one, such as an upcoming turn or overtaking someone.
If you drive 80+ on a 55mph highway, you will almost certainly cause just the kind of shockwaves that are described here, since you can't keep that speed steady, but will have to hit the brakes occasionally, and then the jam starts. Not to mention that you are also endangering other road users with your blatant disregard of traffick rules and need to be fined until you cry. You saving 10-20 minutes is not justification for endangering other people's lives.
It isn't your road, so it isn't your rules either. It is a public road and public rules - laws, in other words. If you don't want to obey them, then you get off the road, or at least stop complaining about people who do obey them.
The simple solution is to take the train. Commuter trains typically go around 100mph and aren't affected by the rush hour; if anything, the train system is more effective when the number of passenger is high. Highways, autobahns and other single-passenger vechile passageways are fine as long as the number of people using them is small. They are not a good solution for getting massive numbers of people from one place to another fast. They simply do not scale.
Some kind of hybrid road/rail system would be ideal: first you drive your car to the nearest rail onramp, once it is on the rail the rail computer takes over and gets you to the offramp nearest to your destination, and then you drive the rest of the way yourself. This would combine the good sides of trains - speed and scalability - with the good side of cars - the independence from public transit schedules and routes.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.
I used to mull over traffic flow while commuting tollways surrounding Chicago. This latest "news" of course is obvious to anyone who thought about it a bit. I noticed that in bad weather I often got home sooner while also driving slower. When there was some snow coming down that affected visibility the drivers used more "padding" space and the ripple effects from braking were diminished.
william beaty did this in 1998 - with nice animated GIFs too:
http://www.eskimo.com/~billb/amateur/traffic/trafexp.html
Claiming that 'robots' (or some sort of automatic braking) will solve this problem is naive. The mathematics of a situation where traffic is dense is somewhat like a stiff differential, where small perturbations in the local conditions can result in massive changes further up the road. An automated algorithm might help, but it is not a trivial problem.
What is required to solve it is some way to know the conditions on the road a significant distance ahead, so that the speed can be appropriately moderated. A 'robot' that is only aware of surrounding cars will make mistakes similar to a human.
The more interesting question is: Can a few people using a different acceleration/breaking strategy prevent or reverse a phase transition?
I thank you for a well formed response.
;) driving slow in front of ya) is not something that reflects on maturity or not. Any person can try to make themselves sound like the most "well restrained" and most mature person in the world but it doesn't work that way over time. Everyone has good and bad days, and on some days an individual is more short than others. If that is wrong or abnormal, then supposedly the entire world is wrong or abnormal.
First off I'd like to say, that simply being frustrated by a condition that is out of your control (dumbass - or dumas
Violence may be a pretty stupid thing, but I think that would go far beyond the definition of "road rage" and more into the definition of Violence.
I was also talking about avoiding collisions. What is your point there? (confused)
Also, driving faster does not risk other people's lives. If you are driving faster and others are not, then your braking will not affect anyone. If you are traveling faster than the speed of traffic then where is this magic shockwave? what is wrong with people driving faster for their own benefit? Are you saying all lanes would go faster if they all go the same speed (because such a concept is impossible at best anyway).
Example of the shockwave in real affect is a railroad track by me....busses stop before they go over the tracks and for some stupid reason when the bus opens its door, people often stop as well (sheeple as always). This causes traffic to back up as far back as 2 miles, as observed by myself and someone coordinated on the other side. Is this safer? no. Numerous people have gotten into accidents from sudden braking going over the tracks as well as vehicle damage from going too slow over the tracks, in fact.
Driving at a steady speed is at best, unrealistic. Nobody can drive at the same speed all the time or we wouldn't have stoplights/stop signs, or turns for that matter. 6billion commuters are not flying airplanes to beeline to their destination. Lets be real here.
Commuter trains go 100MPH? What trains (maglev excluded) are you thinking of? Mass and velocity concerns come to mind here.
I think the rail idea like you're thinking is likely hard to implement but I am not qualified enough nor do I hold an opinion on whether its viable or not. I would say you're looking a bit too much into a certain Tom Cruise movie with that one, however.
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.
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.
Why is this the only topic where slashdotters tend to go all "what about the children?"
Maybe you're being tailgated because you're driving 20mph? Seriously, 20mph school zones are the result of a bunch of overprotective PTA moms who are convinced that everyone is out to get their precious kids, and lowering speed limits to absurdly low levels will solve the problem. Everyone driving 30mph in your 25mph zone? Simple, lower the limit to 20mph and suddenly everyone will be safe! Or at least it'll be easy pickings for a police officer.
Anybody want to run the numbers on how many feet it takes to stop from an HONEST 25mph? If you're too dumb to stop from 25mph when a kid darts out in front of you, 20mph ain't going to save you. I'm not advocating blowing thru school zones, just that 20mph is absurdly slow. It's not reaction time + braking distance, because you don't react to a child magically appearing in front of your bumper, you begin braking as they dart off the sidewalk and you stop before they even get to the street. In a couple hundred thousand miles of driving, I've NEVER had to avoid a child. Overprotective parents in gated communities just want you to think you're a muderous maniac. When I am in a residential area, I slow down out of respect and caution. When I am somewhere that kids are playing, I slow down more to be careful. But I sure as hell don't spend my time comparing my speedometer to some arbitrary limit. It's called judgement.
If you want a simple rule, just drive 20mph in every school zone, obey every speed limit and sign, stop paying attention, and when you run over some kid because you were monitoring your speed based on a sign and not on conditions, you'll avoid jail time because you weren't breaking the law. Congrats. I'd rather change my thinking to avoid killing anyone to begin with. I can live with a speeding ticket, I can't live with killing someone because I didn't exercise caution. Hear about that guy in Seattle who killed a pedestrian and just got off with no jail time? He was a concerned parent with a kid in the back seat, talking on his cell phone, of course not paying attention to the crosswalk. He hit a bicyclist 2 years earlier. But I bet he's real good at watching speed limits and complains about dangerous speeders!
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'd have to see it to know if I wanted to defend it, but if otherwise reasonable people are tailgating you when you get off the freeway, maybe they don't want to drive 30mph on a ramp for a mile just because you feel like driving really slow on a one-lane straight ramp. I think the fact that they don't normally tailgate indicates that maybe you are wrong and they are right. On my way to work, the exit-only lane (still part of the freeway) is well over a mile long, and everyone just starts driving 50mph for no reason even though we are still on the freeway. Talk about maddening. And 30mph is not fatal crash territory unless you hit a concrete wall with no airbags. If someone rearends you at that speed, there will be at most a minor bump, and if you're a crappy driver you might lose control and skid to a stop. Sorry, but roads where everyone is driving the same direction and speed are not where you should focus your concerns. You should worry about a head-on or being t-boned.
I think the root cause for all this is a lack of re
scientific american frontier covered this. Couldn't tell you when, but I'm almost positive that they did.
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.
:P
I'm going to assume you do not commute during, between, before or after rush hour in any major metropolitan region. Otherwise, your statement just doesn't make any practical sense.
60mph == 88 feet per second.
You are recommending a gap of 180 to 270 feet between yourself and the car in front of you. Nevermind the fathomless distance that this veritable FOOTBALL field represents, assuming that a typical car is 20 feet long and we generally leave two car lengths in front of us while in motion, you are inviting 4.5 cars to squeeze in front of you.
Of course, that last 0.5 car is actually a full car so you'll need to back off a bit, requiring use of your brakes and thus inducing exactly the sort of traffic gridlock that we're talking about.
The fact is, when in traffic, you have to drive as traffic does. Deltas in speed, acceleration, braking, even behavior, induce gridlock.
Wouldn't it be nice if everyone left 2-3 seconds in between cars? Of course! Then we'd all be driving the same!
But let's play with that for a minute.
The carrying capacity of a freeway lane is generally measured in cars per unit of time. Following the two second rule and assuming a 20 foot car length, we get... huh, roughly one car every two seconds! I'm not even using math here! So that means that at ANY speed, the maximum number of cars we can accommodate is 1 per 2 seconds per lane. Or 1800phpl (per hour per lane). Which would be fine if we designed freeways accordingly.
But we don't. We don't design freeways, we inhibit their expansion at every turn and by the time said expansion is done, it's way under provisioned. We live with a perpetual shortage of freeway carrying capacity.
The only workable solution available to the average driver, which we arrived at collectively, is to reduce the gap between cars. By reducing that gap from two seconds to one, we practically doubled the carrying capacity of our local freeways... when people behave the same way.
It's possible that mixing two-second-rule drivers with one-second-rule drivers is the cause of this gridlock, but I really don't see any other way given the shortage of lanes.
Oh wait, yes I do. I ride a motorcycle.
These opinions guaranteed or your money back.
My personal solution is to restrict automatic transmissions to the handicapped, and regular testing for elderly drivers.
sic
....mentality that says "I don't want a bus stop near my home" and it has some meritInteresting. Being close to public transport is considered a desirable thing where I live (Melbourne AU).
Giving in to that frustration when in control of half a ton of moving steel, however, does mean you can't be trusted with it. It's road rage, not road frustration.
I got the impression that you were talking about collision survival equipment - seatbelts, airbags and so on.
Yes, it does: you have more kinetic energy, less time to react to problems, harder time of making accurate perceptions...
The cars behind you can't wait to see how hard you're braking before hitting their own. They see your braking light, they have to hit theirs, or risk collision if you're braking harder than they guessed. The cars behind them do the same, and there you have it. A completely mundane, non-magical shockwave.
The danger it causes to others.
In all likelihood, yes. It is, after all, the whole design idea behind highways, motorways and such: separate traffick streams going to different directions from each other, so that the cars close to each other have as little speed difference as possible between them, and you can rise speeds.
You don't see many stoplights or stop signs in multi-lane highways, do you ? And it's not the question of driving at a constant speed, it's the question of driving smoothly, rather than the jerky full forward/full stop style. Coast to the red light, and it might change before you reach them, allowing you to drive through without stopping, for example. It's the jerkiness which causes the shockwave and the jam, not speed change in itself.
Finnish commuter trains - the newer models, anyway - have information displays showing messages, the next station and current speed. The typical speed between stops is around 160km/h, or 100mph. Of course they could be lying.
Mass isn't really important to an electric train, since each wheel on each car can have its own motor, causing total available engine power - and thus acceleration - to scale with the size of the train. The choke point becomes the power grid, then.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.
... whatever happened to that old chestnut? I grew up hearing that shit, and it took. WTF.
Because that might make things worse - people may get even more careless or distracted while driving: why do *I* have to watch the road when this little radar-thingy will brake for me? I bet that some drivers would become more aggressive accelerators if they had an automatic braking system, and would result in even more rapid starts & stops because they would basically just stand on their gas pedal the whole time. This would increase the wave/ripple/accordion effects being discussed here.
-=- James.
....mentality that says "I don't want a bus stop near my home" and it has some merit Interesting. Being close to public transport is considered a desirable thing where I live (Melbourne AU).A retired NYPD (New York City) Cop explained to to me this way. If I want to get into the city I can take the Long Island Rail Road (commuter rail). If their is a bus stop in front of my house I will still drive to the rail station, but I have the sort of people that take the bus standing in front of my house.
Now I will say that when I took the bus in Suffolk County New York, I did get the distinct feeling I was the smartest, richest, best educated person on the bus and I was making about half median US income at the time. When I took the bus to Queens (part of NYC) in High School their were students, working poor, working class, and processionals on the bus. So his claim probably had merit since he lived outside of an urban area.
Now police officer is one of the few professions that someone with 90 college credits can get free parking in Manhattan, and they generally only get on buses and trains to deal with crimes. So I can understand why this and many other cops feel that one should drive if they can afford a car.
--- Justin Dearing http://www.justaprogrammer.net/ We're just programmers.
No time is wasted, if you enjoy being with yourself.
It's not wasting time, I'm educating myself.
Yes, you can close the gap. By reducing speed. I reject that the only way to deal with freeway congestion is to engage in reckless driving.
As far as increasing carrying capacity, we need more areas to focus on multiple approaches--effective public transportation, HOV lanes, carpool programs. Too many people are driving, and too many people are driving alone. But the lack of capacity should lead us to go slower, take a long time to get home... It shouldn't lead us to trying to kill each other.
http://nerdcartoons.com/
...the sort of people that take the busAnyway - there is a difference between "close to" and "right outside". I wouldn't want right outside, especially a train station if only for the noise. But generally "close" is good.
I'm positive that I've read such findings in the ADAC's bulletin in the early 1990s... I also recall getting taught about this effect in drivers school in the mid 1990s...
So what's the new point of this study?
(For non-Germans: The ADAC is a car-users society.)
Screw the FSM - Real geeks believe in the Invisible Pink Unicorn
Well I can (and often do) walk to JFK airport from my house so a train can't be worse than a low flying plane. My grandmother said the concord was much noiser when it first started flying, but it was only slightly louder than a 747 while I was alive. That being said, you get used to the noise, but its an understandable annoyance. Its inconvenient when on the phone or watching TV, but very easy to sleep through. I've heard horror stories of occasional freight trains being forced to stop for whatever reason and blowing their horns excessively at night, but quite frankly, if I was forced to leave NYC proper, I'd love to live in a townhouse that is across the street from a LIRR parking lot.
Having a bus stop in front of your house is only a bad thing if your neighborhood is bad. I would buy the house in front of my bus stop in a heartbeat. Others would cause me some hesitation.
--- Justin Dearing http://www.justaprogrammer.net/ We're just programmers.