Chaos and Your Everyday Traffic Jam 477
An anonymous reader writes "What causes these mysterious traffic jams that continually appear throughout the day for no reason whatsoever? Is it simply the fact that most people just don't have a clue how to drive? That's very possible, and in reality there are so many variables involved in something like a traffic jam. But is it possible that the entire traffic jam could be both the continuing and end result of a chain reaction set in motion by a single driver who was in too much of a hurry?"
Passion of Traffic (Score:5, Funny)
From TFA:
I like the idea of a single blameworthy agent to bear the brunt of my hideous imprecations: a Christ of traffic, if you will; except I'm the Romans, and it's Mel Gibson's Passion all over again.
Specific to Albany, NY area (Score:5, Interesting)
In our area, there is a twice-daily traffic jam that has been understood for years, but fixing the road to take away the problem would be ungodly expensive.
There is, actually, nothing technically wrong with the road. The road in question is I-87 (the Northway), and the pinch point is where it crosses the Mohawk river. The Twin Bridges have a slightly narrower shoulder than the highway leading up to them in either direction, but the shoulder, on both sides of each bridge, is still every bit as wide as any of the three lanes going in either direction.
Compounding the problem is that the bridges are (hope this is the right term) truss bridges. There are two convex bowed beams that go over each side of each bridge, and a construct of triangular trusses between them. These are the reason why a change would be ungodly expensive, because you would have to rebuild the bridges.
Anyway, people come to the bridges and slow down because they perceive that the road has gotten narrower, while failing to perceive that this fact is irrelevant. This slowing down leads to the accordion effect that was described in TFA, where successive cars have to apply more and more braking in order not to hit the car in front of them. By the time you are a mile north of the bridge in the mornings (south in evenings), traffic is basically stopped.
The construct that causes all of this trouble can be seen here [google.com] (along with some Google wierdness in the construction of the image).
Re:Specific to Albany, NY area (Score:4, Interesting)
Site jammed up (Score:5, Funny)
Re:Lane merges (Score:4, Insightful)
Of course if everybody would just make space and bread-n-butter'd at the merge point like they're supposed to, I wouldn't have to go to all that trouble. But hey, it works. Neither me, nor neither of the people in the slow lane next to me have to come to a complete stop. And as for that honker behind me, he's only four or five cars behind where he wanted to be. What is that, like 20 seconds of travel time? Small price to pay for good flow, if you ask me.
BTW, I got the idea from watching how truckers do the same thing at a lane closure. I noticed that the fastest I ever got through the ship channel bridge was when two trucks drove side by side right up to the merge point, and then the one just hit the gas a bit and got ahead of the other. Nobody slowed down, and everybody pretty much got the point that there was no way to get around these guys. Sure we never went really fast, but we never stopped either.
Even this isn't foolproof though. Some idiot actually jumped a curb just to get around me. And you know what? When it came time for her to merge, nobody let her in until about one car ahead of me. Gee, she really got far! Idiot. And then there was another guy who was behind me, got in the merge lane, went over one more lane (causing much honking and screeching of brakes) and then got back in the merge lane where I was going to go just so he could continue giving me the finger. No bother. Just slow down a little more and take the next spot back.
I know, I know!! (Score:5, Insightful)
"What causes these mysterious traffic jams that continually appear throughout the day for no reason whatsoever?
Too many cars?
It's both! (Score:2)
If some bonehead makes a bad driving maneuver, he might cause a traffic jam. And whether or not he actually causes a traffic jam is dependent on how many cars are on the road!
This whole thing is just dumb. Yes, if all drivers drove perfectly, then we could push more cars through the same piece of road. But that's not the way it works. Roads don't have a hard capacity. As the number of cars on the road increase, the chances of a traffic-jam-causing event increase. The more cars, the greater probability of a jam. Maybe at 120 cars a minute there's a 50-50 chance of a jam, but at 140 cars a minute a traffic jam is virtually certain.
So, if cars were driven by perfect-driving robots instead of people, we'd could put more cars on the road without traffic jams. Thanks Slashdot!
Re:It's both! (Score:2)
But if there is a traffic jam, you aren't going to be pushing 140 CPM. I have a feeling that CPM will stay mostly constant and the speed will vary inversely with the total number of cars. Therefore, you would never get enough cars going fast enough to hit a CPM that makes a traffic jam certain (self-limiting). Or maybe it's late and I'm going crazy.
Re:It's both! (Score:2)
If someone decides to drive slowly that reduces the capacity all the way up the road behind him. Similarly if (as seems to happen a lot around here) the authorities put an artificial speed limit on the road for 'traffic management'.
If you have 120CPM, and the road capacity is 140CPM - no jam.
As soon as someone decides they're too scared to drive at the speed limit.. road capacity drops to 100CPM.. jam.
Two seconds? Not during rush hour (Score:2)
Re:It's both! (Score:5, Interesting)
BUT -- and here is where it gets stupid for real-world conditions -- that braking scenario assumes that you must stop within that two-second gap. Think about this: the only way that would matter is if there is an immobile object two seconds ahead of you. You're driving along, then mysteriously, 315 feet in front of you, something is stopped dead. What are the actual chances of this happening to any responsible, alert driver doing 70 MPH? Very small. In fact what will happen is that the car ahead begins to slow, and you burn your 0.4 second reaction time (which I also think is unrealistically high), then you begin to slow in concert with the car ahead. It is obviously impossible to derive any specific numbers for the rates at which this happens as they'll be random, but it certainly doesn't equate to a 70MPH-to-zero panic stop in a limited space.
In any case, his figure of 120 cars per minute is probably a lot closer to reality than anything provided for by the 2-second rule, which is a 24-car-length gap -- have you ever seen a busy highway where anyone was maintaining a 24-car-length gap? Would it even be possible to actually estimate and maintain this at 70 MPH? That's about 1/16th of a mile
Re:It's both! (Score:2)
One of the 2 accidents I've witnessed was exactly that. Car stopped in the road, jackass SUV driver floors it to get into the other lane without slowing down just before he would hit it, tiny car behind him doesn't know there's something stopped in the road until the SUV ducks out of the way. If he had the two seconds, he'd have been able to stop. He didn't. So in my experience, 50% of accidents are what you described.
Re:It's both! (Score:4, Insightful)
The SUV driver should have at least touched the break to clue in those behind. That he didn't is deserving of having his driver's license taken away.
This has nothing to do with car separation. It just so happens that an idiotic separation of hundreds of feet would have helped in this case.
People who drive feeling as though they are _moving through traffic_ are what causes problems.
You should drive _with_ traffic, be a _part of traffic_. There are no individuals in traffic - we are all one whole. The Traffic.
Drive with this in mind, and you'll increase your driving skill by orders of magnitude.
(Of course none of this _really_ matters even if it is the truth, because of all the other individuals considering themselves the most important pricks in traffic / the universe...)
(And yes, this means that I break speed limits whenever moving with traffic requires it. This is a natural conclusion.)
Cheers.
Re:It's both! (Score:3, Insightful)
I've also been in an accident exactly like this - the van in front of me moved right - voila - about a 5 mph pickup in left lane, 18 wheeler right next to me - 55 mph smashup. It was a pretty hefty wreck, threw the pickup about 300 feet, totalled both vehicles. I was not found at fault, since it was a 55 mph road with no turns at that point, and pickup was moving far below stated and reasonable speeds. (FYI: No one was hurt in any meaningful way)
I've driven in the US, Canada, Mexico and a large segment of Europe, and by far, the best freeway drivers are in Europe. They drive right most of the time, trucks are limited to right lane(s) only and a max of 50 mph through large segments of freeway, and in general are far more considerate than the embecilic god-given left-lane road hogs in the US. (Then again, failure to drive right in Europe can result in incredibly horrible accidents - a mercedes plowing into a BMW launched over an Opel hatchback at a 100mph speed differential is not a sight you want to see. The Opel pulled into the left lane just in front of the BMW.)
Your largest problem on crowded US roads are trucks. Their braking/speedup times are significantly slower than cars, and will cause massive accordian effects the first time they brake. Move them to the right and limit their speed and following distances, and entire problem segments will dissappear. It may slow overall traffic but it will be a steady pace, which will be much faster than the accordian stops otherwise always experienced.
Re:It's both! (Score:4, Informative)
the assumption is that the average person requires about 2/5th of a second to react,
That's very fast. Reaction to an unexpected event is 0.5-1 second. Most safety studies put 1 second as the reaction time.
What are the actual chances of this happening to any responsible, alert driver doing 70 MPH?
Responsible and alert drivers are the minority. Rules are made for everyone, so they take into account the fact that people is chatting with passengers, looking at the mountain on the left, thinking about their children, and so on. When you factor in the boringness of a long drive and all the possible distractions, even 1 second may be too low.
You need to plan for the worst case, not for the best.
Re:It's both! (Score:4, Insightful)
Re:It's both! (Score:3, Interesting)
You have obviously never driven on 880 through the East Bay between 6am and 8pm.
In my opinion you can frequently blame random mass panic stops on on guy who's already home snacking and watching the tube, because the guy to blame is an idiot traffic engineer that works for the state, and they get to go home at 3:30pm.
Seriously..
In all the years I've driven I've decided that traffic flow is analagous to a special case of internal compressible flow. That is the mechanical engineering way to say it's like supersonic air flow in a pipe. The special case is that there is no friction with the walls of the pipe and that the pipe is very small in diameter. When traffic is at a sufficient density and speed, a constriction, or obsruction can cause a shock to occur. On one side of the shock traffic is "supersonic," on the other side it's crawling along, and at the shock everyone is standing on their brakes hoping they won't get rear ended by that idtiot in the SUV with the cell phone and starbucks. Shocks can be static. This tends to occur when there is no change in total mass flow rate across the shock. A moving shock occurs when there is a change in mass flow across the shock. If total trafic flow rate is slower downstream of a shock then the shock will move backward through traffic until it reaches an equilibrium point. Sometimes you get a bad phenomena that I call cascading shocks. That's when some constriction causes a shock for just a moment. That shock, if the traffic is of sufficient density and speed, travels backwards through traffic, but since the source is temporary, or periodic, traffic accelerates again (since gas flows don't accelerate on thier own, that is where the analogy breaks down). Then the disturbance occurs again and another shock starts moving backwards through traffic. One example of this that I can think of is on 880 south approaching the San Mateo Bridge turn off. 880 tends to be very fast and very high density. There is a carpool lane. Frequently a jerk waits as long as possible in the carpool lane before frantically changing across all the lanes to exit to the Bridge. This causes a moving shock, and so does the next jerk... This is why on that freeway everybody will be doing 70 one moment and the next everyone is standing on their brakes, hoping the sphincter will hold. A moment later everyone is going 70 again, and sure enough here comes another panic stop.
So clearly in flow that has a critcal density and speed, any sufficiently large perterbation can cause a traffic slowdown. Chaotic effects clearly come into play.
Re:I know, I know!! (Score:3, Interesting)
No, it isn't possible that a single driver could be the cause. The mechanism described in the article relies also on a large number of other drivers all following too close to the car in front. If enough people kept a safe distance from the car in front, the shock wave caused by the sudden movement of one car would die away instead of being amplified.
Aside:
There's no justice in motoring. Responsible drivers just have to get used to the idea that they can help avoid jams and accidents, and they themselves will get less benefit from their own responsible actions than will the idiots who cause the trouble in the first place. The idiots won't even realise they've done anything wrong...
Re:I know, I know!! (Score:2)
Re:I know, I know!! (Score:2)
Definition of "cause" [reference.com]
1. a person or thing that acts, happens, or exists in such a way that some specific thing happens as a result; the producer of an effect: You have been the cause of much anxiety. What was the cause of the accident?
"The producer of an effect" sure as hell sounds like "set in motion" to me.
Re:I know, I know!! (Score:3, Interesting)
Another thing people don't seem to realize is that "more roads" or "wider roads" won't usually constitute a long-term solution to traffic problems. It just leads more people to plan around the roads having higher capacity, so more and more people plan on using the roads, until they're choked up again. See my last journal entry.
Re:I know, I know!! (Score:2)
Their system simply doesn't work. I've so often seen the situation clear road -> 60mph limit (jam) -> clear road that I can even predict the jams from the signposts now.
You have a road that is flowing freely at somewhere approaching (say) 85-90% capacity. Then you put a 60mph limit on it. This reduces the speed limit by ~15%.. simplistic calculation - reduce the capacity by 15% on an 85% capacity road. That ain't gonna make the traffic flow more freely. WTF are they thinking?
What's worse is if they continue this for a long time (sometimes they leave these limits on for days.. heck, there's one not far from me that's been the same for 3 months!) the jam backs up all the way up the motorway beyond the limit, backing up into the roundabouts and causing further jams on the roads leading up to the motorway.
Re:I know, I know!! (Score:3, Interesting)
Re:I know, I know!! (Score:2, Insightful)
Re:I know, I know!! (Score:2)
I don't agree with TFA that the 'ripples' will propogate very far - that relies on everyone tailgating, which really isn't going to happen - a percentage of drivers will be at a proper 2 second gap.. and even though that's (sadly) the minority each one of those will cushion the affect, causing it to die out fairly quickly.
Where I live ... (Score:2)
In a community of about 70 people covering 50 square miles, it's not hard to imagine why traffic jams are nonexistent.
I used to live in Houston. After years of moving back here, I've nearly forgotten what traffic jams are like.
Around here, the closest thing to a traffic jam is me. Even the old people think I drive too slow.
Re:Where I live ... (Score:5, Funny)
It's not the waiting that's so troublesome about a traffic jam, nor is the fact your boss will be very angry about you being 3 days late for work. It's the seeing other people's weird-car-habbits that's truely painful.
Luckly there are a few ways to make it less painful:
1) Bring your wife. Get her head in your lap. Remember to "read" a map or newspaper at the proper time. Nobody wants to see your face at that particular moment.
2) Bring your kids! Yelling and screaming is very good to get oxygen in your system and the kicking might actually get your lower back pain to disappear. People tend to pay a lot for such a massage.
3) Portable TV! Makes your waiting in the jam a painless affair. Might, ofcourse, make you the cause of the next traffic jam.
4) Laptops! Pass the network cable from car to car and have a mobile LAN-party!
5) Cellphone: Ask the number of other people in the jam and have conversations. Now you can ask what the h*ll he was thinking and discuss why he should stay the f*ck on his lane.
6) music intruments! They call it jammin' right?
7) Mexican wave
8) strip poker with car parts! A El Cheapo car with the hood of a ferrari, now wouldn't that rock?
9) Bring candy and beer! Instant party! Would suck if you're picked to be the sober driver. Thought bringing drunk friends home was bad? Think how bringing 12,000 drunk strangers home would be like.
10) Disassemble your car, climb over the fence, down to the street below with as many part as you can carry. repeat as necessary. reassemble the car. Takes some time, but you'll be home quicker anyway.
Re:Where I live ... (Score:3, Funny)
Field of Study (Score:4, Informative)
This mainly deals with optimizing freeways and the like, based on people's behavior in traffic, and the ripple affects.
Re:Field of Study (Score:2)
If only we could get carpool lanes in Las Vegas where I live. If only they'd study traffic here right to find out how badly we need those -_-
Re:Field of Study (Score:2)
Those are the lanes at the side of the road that are a few miles long and are mostly empty throughout the day, right? Or where people drive bumper-to-bumper at a barely noticeable faster rate than the folks driving bumper-to-bumper in the regular lanes?
Personally, I think everyone in the LA area should get get over the political correctness and shitcan the idea. No one carpools (except by accident of circumstance) and no one ride shares, and if the money wasn't taken from the kicking and screaming residents, there would still be zero public transportation. In other cities, typically those without the seemingly insurmountable sprawl that defines most all of the LA basin, car pool lanes do work. Oddly, those cities have better roads, less congestion, better drivers, lower car registration fees, and lower fines. Go figure.
As for the subject of "traffic analysis," I've read about case studies where neighborhoods and/or regions have been dramatically improved by the act of "synchronising" traffic lights. I don't know enough about the subject or the practice to offer a comment, but I doubt there's anyone who hasn't noticed that driving through any area with moderate traffic, the lights seem to work OK, but come 4-5:00pm (or 6-7:00am), irrespective of traffic flow, the lights start turning read with increasing frequency, and traffic starts backing up. My guess is there's a BOFH version of a traffic controller in every city doing it on purpose.
Re:Field of Study (Score:3, Interesting)
As I understand it, you are sort of correct. Lights are timed to slow cars down at rush hour to reduce the number of traffic accidents, resulting in a net increase in the average speed of traffic at rush hour. There is also the concept called "metering lights" which are stoplights on the freeways (bridges mostly) in the San Francisco Bay Area, The Idea is to get some space between cars so that they will move faster.
Despite kicking and screaming... (Score:3, Interesting)
This is why when the price of gas went up, and people actually tried the Red Line and Metrolink and other parts of our old/new (most of the right-of-ways are old Pacific Electric right-of-ways) light rail infrastructure, people started talking about how nice it would be to have the Wilshire spur of the Red Line finally take its intended trip to Santa Monica. The Expo Line between USC and Culver City (with an extension to Venice on the drawing board) is being built now. It links with the oldest of our light rail lines, the Blue Line, which goes down the Alameda corridor through some of the nastiest neighborhoods in LA. And yet: the Blue Line gets a lot of use. Why? It's the easiest way to get to Long Beach.
We have our ill-advised lines too: the Green Line which boneheadedly does not go all the way to LAX, and the Gold Line which is a good route into Pasadena from Downtown but is slowed to a crawl by nervous NIMBYs who don't have the good sense to tell their kids to GIVE RAILROAD RIGHT-OF-WAYS A WIDE BERTH. "Oh, those Blue Line trains go so fast and we see lots of people killed on the 6:00 news...oh please, City Councilperson, make 'em run the trains at 15 miles per hour in our neighborhood!" Dumbasses. You can't outrun a train, either on foot or in your freaking car. Grow a freaking brain.
We need light rail. It made sense when they put the Pacific Electric in back in the day, and it makes even more sense now. With Peak Oil on the horizon it's time. When gasoline hits $5 a gallon maybe even the NIMBYs will have a nice warm cup of STFU and get on board.
Roads and CSMA/CD (Score:5, Insightful)
With Ethernet, as the 'traffic' builds to about 40% of the theoretical capacity, collisions become the norm and the re-tries start to overwhealm the system and it locks. With roadways, as the traffic builds to a certain limit, then awareness of potential collisions magnifies in the drivers, so reactions to situations increases and the road stalls. This is why variable speed limits work, because the road and drivers can cope with more vehicles if there is a lower maximum speed.
Re:Roads and CSMA/CD (Score:5, Interesting)
> I'm inclined to compare roads to shared medium Ethernet. As the
> traffic builds up you get more 'collisions' and both systems
> have collision detection built-in. With Ethernet, as the 'traffic'
> builds to about 40% of the theoretical capacity, collisions
> become the norm
You're pretty much completely wrong, and the last quoted line sums up why.
Collisions are not the norm in traffic jams.
Traffic jams happen due to the ripple effect from cumulative reaction time
delays in response to changes in traffic. The effect accumulates until there
is so much loss of speed that people drive closer together. Then when they
have to react, they react more abruptly, and that causes yet a stronger ripple
effect.
Packets collide, cars don't. Cars change speed, packets don't.
Well, OK, sometimes cars do collide. But it's not the collision itself that
causes the traffic jam, it's the bottleneck in the right of way and/or the
rubberneckers.
If people could and would simply maintain the 2 second following distance
no matter what speed, when the fewer traffic jams did occur, they would resolve
themselves much more quickly. But just try telling the person 500 cars back to
just sit still for 10 minutes. They'd probably want to punch you, and they'll
still insist on driving stopgostopgostogostopgo despite the fact that doing so
means they'll be doing it for several times longer than just waiting.
90% of drivers think they're better than average.
90% of drivers are below average drivers.
So I give free driving lessons.
Like braking suddenly for tailgaters.
Re:Roads and CSMA/CD (Score:2)
http://science.slashdot.org/comments.pl?sid=21373
i have just submitted much better than myself.
Re:Roads and CSMA/CD (Score:2)
no matter what speed, when the fewer traffic jams did occur, they would resolve
themselves much more quickly. But just try telling the person 500 cars back to
just sit still for 10 minutes.
The two-second rule is unrealistic for many reasons. I broke it down in an earlier post, above, but basically two seconds at 70 MPH is a 24 car-length gap. That's 1/16th of a mile. Can you imagine the complexity that would be necessary to account for cars entering and leaving traffic, complete with acceleration and deceleration into and out of the existing football-field-sized gaps, all while maintaining this magical 2-second gap? It is pure fantasy. Sure it would eliminate traffic jams if it was possible -- mainly because it requires eliminating most of the cars on the road.
Re:Roads and CSMA/CD (Score:2)
Like braking suddenly for tailgaters.
This is why people who actually give driving lessons tell you that your job as a driver is to watch the road ahead. Let the guy behind you worry about his own driving. Without exception the worst drivers I have ever seen are the ones who are preoccupied to distraction with whatever is happening behind them.
Re:Roads and CSMA/CD (Score:3, Interesting)
90% of drivers are below average drivers.
So I give free driving lessons.
Like braking suddenly for tailgaters."
For irresponsible people like you who play fast and loose with the lives of other people on the road I have a favorite past time. I like to call it "Civic Lesson 101" or YANA (Your Ass is Not Anonomyous.)
What many people fail to recall (or do not know in the first place) is that their license plate number is linked to the public record of their automobile registration. Just as a police officer can access your records from his cruiser by entering your license plate into his computer, so I can access your public record from any PC with an internet connection.
Your public record contains useful data on how I can get in touch with you such as: your address, your full name, when and where you bought your vehicle, and what finance company is financing it. Sometimes it even has your phone number listed; however this is a convenience as a few moments with Google is just as effective. Someone motivated by sinister desires, vengeance, or worst of all a sense of justice could wreak incredible personal, financial, and even legal harm with these details. For me the mere inconvenience and/or uneasiness of the perp is enough. All I want is to remind them...YANA: act appropriately.
At this point the options are wide open. If the trangression was eggregious enough (road rage or say blocking the left lane on a multilane highway while driving under the speed limit and then aggressively braking) there can be severe penalties. In highschool we would grab a few friends, scrape together $40, buy 4000 forks, and then carefully stick them into the front yard of the offending idiot. Others have had fun with rock salt on the grass, but I draw the line at destruction of property.
As an adult I use a more civilized approach. Simply send an anonomyous letter addressed to the family of the perpetrator detailing the incident in question and how you attained their home address. Polite reminders about what someone of a more violent disposition might do under these circumstances are unnecessary. The imagination of the recipient of the letter is sufficient in this respect.
A follow-up phone call during business hours may or may not be necessary, though it is undeniably effective. The idea is to sound as a voice of reason, acting in the interests of public safety. Always be polite, professional, and as unemotional as Hal9000. Briefly describe the incident and ask the perpetrator (or better their spouse) to stop driving in that manner. You only make the phonce call AFTER they receive the letter, otherwise they tend to get hostile and quite rude. The letter tends to bring people down a notch as they realize that they are exposed while you, the slighted party, remain anonomyous.
Whether or not this has any lasting effect is unknown, however I think it does make people a little more aware that the vehicles they toy with on the road actually contain human beings...and remember that humans are unpredictable and...YANA.
Re:Roads and CSMA/CD (Score:4, Informative)
It's a series of tubes! (Score:2)
Clue (Score:2)
YES! But that's not news, we have known this for over a century now...
On a very busy road... (Score:5, Interesting)
Quite often when it is very busy, you can see a standing wave in the traffic - there's an area where all the cars are stopped - but there is NO obstruction at all. The cars are filling the 'standing wave' from the back as quickly as cars at the front are leaving it - so it becomes self-sustaining.
When the road is full to capacity, moving at 70 mph, all it takes is one person to jab their brakes
The other problem is lorries (large trucks) overtaking lorries with a speed differential of 0.5 mph. It takes them several minutes to get past because they are both speed limited within 0.5 mph of each other, meaning the inside two lanes are 56mph, and the outside lane is 70mph+. When a frustrated driver pulls out into the outside lane after being stuck behind a lorry for "too long", they cause one of the outside lane drivers to brake down to 56 mph quite suddenly. This can easily get the 'braking cascade' started, and before you know it - you have a standing wave traffic jam with no actual obstruction (other than the standing wave itself).
Usually then what happens, is the opposite direction traffic, seeing the stoppage rubber necks for the possible accident. An inattentive driver looking at the other side of the road finally looks back in front and realises he's about to ram a truck in the rear and slams on the brakes. The driver behind him following far to closely has to brake even harder - and there's either a shunt or if they are lucky, ANOTHER standing wave traffic jam starts on this side of the road too.
It's fascinating to watch from the air. Frustrating to be in when driving.
Re:On a very busy road... (Score:5, Interesting)
Just ask anyone who has been a driver at the tail end of an Army Convoy. They are either flat out of at a dead stop. The concertina effect magnifies as the number of vehicles increases. This is why smaller convoys are better.
I was once in a lecture where this was explained. It all went down to the following
Chaos Theory
Queuing Theory
and most impostantly,
A single thing which cause on vehicle to slow down without due cause. The nthe vehicle behind has to slow and Bingo! it all starts.
Once to get beyond a certain number of vehicles the elasticity in the queue gets to a critical size and you get the unexplained traffic jams.
Some places try to minimise these jams by artificially reducing speed limits to reduce the elasticity but IMHO, these have limited effect.
IMHO, the ONLY way to stop these elastic jams is to connect the vehicles together. I once saw a demo of such a thing. Oh, sorry, it is called a train...:)
Seriously, BMW demoed a device many years ago that would allow you to get much closer to the vehicle in front but in a safe manner. I think that it is only a metter of time before there is a viable system to connect vehicles together electronically in such a way that they can be physically very close to each other in a safe manner. The driver would join such a convoy and then switch on an autopilot system and sit back and relax.
Re:On a very busy road... (Score:2)
Re:On a very busy road... (Score:3, Interesting)
There's an old article on this, with animations, here [amasci.com].
Try and be part of the solution.
Re:On a very busy road... (Score:5, Insightful)
The art of proper merging should be something taught to drivers and tested on the driving test.
Re:On a very busy road... (Score:4, Interesting)
Even more, it's not helped by people letting in the drivers who go to the end. Personally, I'll let people in when they try to merge soon after noticing the obstruction. But if they try to cut in at the end, I'll ride the previous car's bumper to prevent them from getting in, and give them the finger to boot! And if that makes me a bastard, that's fine with me.
Re:On a very busy road... (Score:2)
Re:On a very busy road... (Score:3, Interesting)
And that reminds me of a major gripe I have. In some places, usually where there is an offramp and an onramp that share a lane for a tenth of a mile or so (ie, they cross,) if there is standing traffic in the travel lanes I will encounter some drivers who won't let me merge from the onramp. I mean, where the hell am I supposed to go? It's not like I'm trying to cheat anyone out of their spot or anything! My lane disappears into your lane...what do you want me to do? Idiots. I can only imagine that these people have very small worlds, and take it as some sort of defeat that a car was able to get in front of them.
Re:On a very busy road... (Score:2)
I do the exact same as you - and frankly I really could not care less if they dent the body work trying to force their way in I dont plan to move out of their way - the car isn't mine, I can't lose any no claims and it wont cost me a penny to fix.
Its a variation of "the car with the worst body work has right of way" rule
Re:On a very busy road... (Score:2, Insightful)
Re:On a very busy road... (Score:4, Informative)
Re:On a very busy road... (Score:5, Interesting)
Re:On a very busy road... (Score:2)
Professor Helbing (as mentioned on that page) gave a talk at ALife X this past year. Normally, we're all about artificial biology and dynamical systems and stuff like that, so Helbing considered himself something of an outsider. But the emergent properties of traffic flow and the dynamical systems involved were actually a quite natural fit with our normal areas of research in the artificial life community.
He talked some about vehicle traffic, but focused more on people traffic. For example, he spoke about problems with people traffic at Mecca, where millions of people arrive at the same time to perform a ritual which essentially involves walking to the center of a large arena and throwing pebbles at some pillars [wikipedia.org] that represent the Devil. The way the arena is set up was conducive to massive traffic jams of people as well as deadly stampedes. At the time, as I recall, Helbing and his team recommended replacing the traditional pillars with wall segments which would afford pilgrims a wider opportunity to perform the ritual. Officials there also built a second layer of walkway near the wall segments to afford more traffic flow.
Of course, this didn't solve the problem of the fairly narrow entrance and exit to the facility, and stampedes in those areas still occur, though with less frequency.
Re:On a very busy road... (Score:2)
This is why I am a tailgater. If I'm coming out of a pile and nobody is on front of me I fix it real quick. I just punch it until 120MPH (about the safest my vehicle can handle in its current state) or there is a car 5 feet in front of my front bumper.
Re:On a very busy road... (Score:2)
Heh, I've noticed the same thing from the ground: the controlled-access part of GA 78 has exactly ONE curve, and that's exactly where the standing wave forms every rush hour. And you know what the worst part is? The curve is banked, so there's no legitimate reason to slow down for it!
Re:On a very busy road... (Score:2)
Re:On a very busy road... (Score:2)
I disagree. It is difficult to judge the speed of another vehicle visually under any circumstances. It is impossible to determine the rate at which another vehicle is braking -- as an AC posted above, brake lights don't give you any information except BRAKE!
It is therefore very likely that any following car will slow to a larger degree.
The "safe distance" required to alleviate this effect has many associated problems. It increases the difficulty of judging the rate of travel and rate of braking of the vehicle ahead. Such distances are difficult to judge and impossible to maintain at highway speeds (the two-second rule equates to 1/16th of a mile, more than a football-field's length, at 70 MPH). Maintaining that gap while accommodating merging and departing traffic is virtually impossible. Such a large gap invites lane changes.
And finally, such enormous gaps (1 car every 16 miles) simply do not allow for the traffic levels -- by that I mean the USAGE levels -- that are required of highways during rush-hour periods.
It's one of those things which sounds great in theory, but is an impossible, miserable failure in practice.
Re:Humm... (Score:2)
Sounds like a very good book. Perhaps we can persuade Ridley Scott to base a movie on it.
Those damn butterflies are attacking America again (Score:4, Funny)
Chain reaction (Score:2, Insightful)
Re:Chain reaction (Score:2)
Seriously. (Score:3, Insightful)
The real "first cause" of traffic jams is differences in driving decisions and style. If everyone drove at 120mph, or everyone drove a 30mph, or everyone could anticipate exactly what the other driver would do before they did it, and adjust accordingly in advance, there would be no traffic jams.
Traffic jams happen because one guy is driving 45 mph thinking "look at all these damn idiots driving too fast for this weather and this level of congestion, well not me, I'm a good driver" and the guy behind him steps on the gas and passes at 80 mph thinking "look at all these damn idiots impeding the flow of traffic, well not me, I'm going to pass so that others behind me can pass afterward" and the guy in the next lane over is thinking "jesus, look at these idiotic fast and slow drivers passing each other and holding up traffic, I'm going to stay in my lane and not accommodate any of them or let them use my lane to pass, since they're all rotten-ass drivers."
It's the conflicting intentions and behaviors in similar situations that lead to brake-slamming, passing, swerving, wrecks, and the other causes of the density patterns that characterize traffic jams.
slow ass drivers (Score:3, Interesting)
The people with really fast cars generally drive very well. After all, they don't want to smash up their fancy car.
It's the assholes who don't care that they clogging up the passing lane who really are the cause of most accidents and traffic slowdown.
Oh, I have noticed that traffic patterns and behaviors do vary by location. For instance in New Orleans (pre-katrina) the drivers were extremely agressive and would not let you in no matter what and pretty much there could be aliens landing on the side of the road and nobody would care or slow down. In L.A. the 405 would be backed up forever only to find out that it was slowed down because of ONE car broke down in the emergency lane, with no accident; everyone was slowing down in response to this one car on the side of the road. In San Antonio, TX, everyone is on crack and drives a Ford F450 Dually 100mph, everywhere. Not usually a problem, but the entire city of San Antonio is being redone road wise and it creates choke points almost instantly that can't be foreseen.
Re:slow ass drivers (Score:3, Insightful)
That's just what the idiot who drives too fast without paying attention and runs into them would have you believe. To make it easier to identify them they have often purchased personalised number plates identifying themeselves by name - at least in my country. If you ram into someone under ordinary conditions you are just not paying attention or do not know how to drive within the capability of your vehicle - if you can't even stop in time for a moving target what chance do you have against a stationary road hazard?
People who drive slowly in the wrong place may be annoying idiots - but they do not cause the accident.
Re:slow ass drivers (Score:2)
That's how the law works in Australia. If you ram a sober, licensened driver from behind your insurance company will automatically admit liability on your behalf, even if you have independent witnesses who saw the arsehole cut you off and slam on the brakes.
Re:slow ass drivers (Score:2)
And that's just what the lazy, self absorbed twats would have you believe.
Here's a clue: People who are driving fast are paying attention to
It's the cell phone talking, radio fiddling, maps reading, inbred fuckwits cycling between 60 and 75mph in the fast lane that are the real problems. They get absorbed in their discussions of which tampon is most absorbent or which ultra right-wing pundit is more correct and their speed gradually drops off. Then they suddenly notice people forced to pass them on the "wrong" side or somebody 6 inches off their bumper. Then, instead of getting the fuck out of the lane and hopefully dying in a spectacular ball of flame, they punch it back up to a nearly reasonable speed in the fast lane for all of 3 minutes before the cycle starts again.
Saying that they don't cause accidents is bullshit. It's like blaming a murder on the weapon rather than the person weilding it.
Slow, inattentive drivers may not be involved in the accident, but they cause plenty.
Re:slow ass drivers (Score:3, Insightful)
Interesting justification for failing to pay attention - is it that everyone else should do it instead or am I seeing things the wrong way here? Why the death wish on a person in front? If someone is knowingly driving 6 inches away at 75mph on a public road with amataur drivers they should not have a drivers licence no matter how many times they've seen race drivers on TV.
Somehow replying to some guy that says the slowpokes cause all the accidents has been read as they cause no accidents - get off the absolutes guys but also remember that driving to put yourself into situations where you cannot control your vehicle can't be blamed on the tree, animal, child or slow driver in front.
Re:slow ass drivers (Score:2)
Re:slow ass drivers (Score:5, Insightful)
Here in Britain, I drive a small Skoda, it doesn't go too fast, but it's certainly no snail (it can do well over 100 if I really wanted to). I tend to drive down motorways at 75 or 80 mph (very naughty, I know, the speed limit is 70). The thing that I observe most often is that if I pull out to overtake some slower moving traffic (a lorry, or someone doing 70), there's usually some ass hole in a beemer, a merc or an audi comes roaring up behind me at 100mph, slams on the breaks because he realises a bit too late that there's someone driving at a sane speed, and then proceeds to tail you 5m from your bumper until you deign to move over and let the selfish twat past.
Re:slow ass drivers (Score:2)
The people with really fast cars generally drive very well.
Ha ha ha ha ha ha ha! Seriously, which universe did you just slide in from?
And this is from someone who has a fast car and drives it as such.
Every model of every car brand has bad drivers.
Anyone else noticing the Mini Coopers have more than their share, though?
Re:slow ass drivers (Score:2)
Re:slow ass drivers (Score:3, Informative)
I lived outside of LA for a couple of years, and found that the OP is correct, and it applies somewhat everywhere. There is an "efficient" speed at which 90-95% of interstate highway drivers find comfortable. This varies slightly with terrain and time on the road (California has coined a term - "velocitation" - for the effect), as you get comfortable at increasingly higher speeds while driving, but is generally somewhere between 75 and 90 mph in good weather. The upper limit has a lot to do with road and wind noise, along with the responsiveness of steering of your car at higher speeds.
The problem (yes, I believe it's a problem in this context) is that the speed limit is generally 10-20mph below that limit. Conscientious drivers and the small percentage who are uncomfortable at speed (generally older drivers, but includes tentative inexperienced drivers of all ages) view the limits as a "reason" to drive slower than the flow of traffic. Yes, yes, speed limits are the law...blah, blah, blah. Stay with me for a minute - we're talking physics and human interaction, not legislation right now. Because a majority of drivers are comfortable driving significatnly faster than the limit, they tend to drive at/near the limit of enforcement, or about 7-9mph above the posted limit. A minority will carefully abide by the law, maintaining the speed limit plus or minus a couple of mph. This creates a differential in the traffic flow, and the result is platoons on single (and some double) lane roads, with the platoon leader, aka slow driver, at the head. Yes, they're really called that, according to the USDOT. In multi-lane conditions, this forms a moving blockage, with a net 10-15mph differential. Looking at it as a particle flow problem, and knowing that the cars going around the obstruction will not speed up to equalize the pressure (think Bernoulli's principle), you get a build up of traffic and an eventual blockage / traffic jam.
Trucks can cause horrible traffic jams in hilly terrain. Here in Virginia, I-81 has some hellacious slow-downs due to a two-lane traffic area and some significant grades. Full trucks will drop to 25-40mph on the up hill climbs, and then do 80+ down the next hill. Talk about a recipe for disaster. Add that to the relative inexperience in dense traffic for most of the local residents, and we have a bunch of accidents. It's not the speed, it's the speed differential. Hitting a tractor-trailer at 30mph is just about as deadly as hitting one at 70mph when there's just a guardrail between you and a 50-200' dropoff in the mountains.
OTOH, on the 210 east of Pasadena outside of LA, it's not uncommon to find 85-90mph "traffic flow" with very few incidents of jams or wrecks. Of the two I can remember, both were caused by a driver either falling asleep or drifting into the guardrail (distracted?), both were "one driver" accidents that led to messes. They probably would have caused their damage if they were going 40. One part is that there is a limited flow volume on 4 lanes - lots of space for the slow folks (i.e. anyone going less than 10 over the limit) and everyone else to have their own lanes. Often there wouldn't be but a 4-6mph difference between lanes. Very orderly, few variables.
Re:slow ass drivers (Score:3, Insightful)
The idiot that is 8 inches from the car in front of him is the cause. plain ans simple. Because if he/she is so stupid to tailgate, then they will cut others off at highway speeds and drive incredibly reckless causing more traffic behind them to slow down.
The one guy putting along NEVER causes the problem.
"Spring Effect" (Score:2)
Isn't it fairly obvious? (Score:3, Insightful)
The only way to get consistent traffic throughput is to have cars that maintain the same speed at all times, do not switch lanes and do not turn left or right at all.
Since all drivers have different destinations, driving techniques, cars and intentions, it is impossible to achieve this. Someone's gonna change to the other lane, delaying the people behind him who have intentions to delay the traffic in some other way, which eventually triggers traffic jam. It's a gigantic chain reaction, really.
Re:Isn't it fairly obvious? (Score:2)
How to help unjam and jam (Score:4, Insightful)
Re:How to help unjam and jam (Score:2, Insightful)
A few other beneficial side effects:
* better gas mileage
* less stress
* less wear and tear on your brakes
Re:How to help unjam and jam (Score:2)
Re:How to help unjam and jam (Score:2)
But we can do better than this. Have you ever noticed those electronic signs on busy roads, where they can display a variable speed limit? If they're being controlled by an intelligent person/system (which is, sadly, not always the case) then they'll have computed a speed at which this will occur, based on actual measurements of where all the cars are, and the signs are showing a limit of that speed.
Ever notice how everybody ignores those signs and drives as fast as they can?
That's why traffic jams happen. Obey the damn signs, you arseholes.
Re:How to help unjam and jam (Score:2)
No, because:
(a) it's illegal
(b) the police *love* picking up people for breaking these limits and are usually staked out along the stretch
(c) half of the signs have speed cameras on them that activate along with the camera anyway.
Did you ever think that, with those resources (Score:2)
Density waves? (Score:4, Interesting)
As a sidenote, I once read an anecdotal story about a guy who always got stuck in the road while driving home from work, and one day he thought about how everybody's trying to get home fast yet everybody gets stuck in traffic, so he decided to experiment by driving a bit slower. After a few minutes he was amazed to find how the traffic behind him was neat and orderly, instead of the usual jumble, which implies (I emphasize: anecdotally) that the behaviour of a single car can not only create, but also avoid the creation of density waves.
Re:Density waves? (Score:2)
http://www.amasci.com/amateur/traffic/traffic1.ht
If it's not, I think you'll like it anyway.
Re:Density waves? (Score:2)
It's too obvious (Score:5, Funny)
Don't go your heads a-shaking now. It's really obvious. The oil companies make a bundle of those traffic jams. Every day just before rush hour a small fleet of inconspicuous unmarked vehicles, driven by selected elderly, are leashed upon the major freeways. They are trained to drive in such a pattern that makes it impossible for other cars to bypass them. Soon enough the traffic jam forms. Millions of cars are burning precious fuel while standing still, and the oil barons go cha-ching.
Denying it doesn't make it go away.
-- Arik
Learn more about traffic (Score:2)
traffic scenarios. I have always seen the creation of a traffic jam as a transition from a high density high flow state meta stable state to a high density low flow state. This can be expressed with a lambda shape curve in a density-flow diagram. The cause for exiting the meta stable state can be a
small disturbance, sometimes simulated by a random factor in CA traffic models, e.g. some guy braking without reason. In reality I don't think you can avoid the transition without maybe the help of computer guided cars.
Maintain a decent following distance!! (Score:2)
The fool who taps his brakes is merely the trigger.
Old, old, incredibly old news (Score:5, Interesting)
Valid reason, but not the main one (Score:4, Interesting)
Most likely the lane was slower because (a) there was a high-inertia-mass truck in front of you or (b) sloppy driver (undercaffeinated, grandma, or just plain unexperienced driver).
This condition could not be helped. The critical condition of the stand-still or bumper-to-bumper traffic jam is caused by concentration of cars increasing certain threshold level. The main factor in this criticality is the distance between cars. How many of us actually follow three-second rule? The tail-gating leads to the high probability of the scenario when the car in front of you breaks and you will be forced to break with the HIGHER deceleration. That leads to lesser control of the final steady speed achieved at the end of the process of deceleration. Needless to say that the chain reaction will continue all the way back with increasing decelaration and decreasing final speeds of deceleration.
The solution to the traffic jam problem is trying to smooth traffic even at very low speeds. To do that we need stricter laws regulating tailgating. It needs to be automatic, the cars should be equipped with automatic sensors, all the entrances to the freeways/highways should be regulated by traffic lights.
Again: the problem with traffic jam is the criticality at certain speed. The only way to lessen this criticality is to increase distance between cars.
The other good way of easing traffic jams is complete abandonment of upper speed limit. That will increase the efficency of the traffic arteries.
Together, tougher tailgating regulation and absence of speed limit, will help the traffic jam situation in the country.
Re:poll time (Score:2)
A multitude of distractions.
Re:poll time (Score:2)
Re:Speed cameras (Score:2)
Re:Speed cameras (Score:2)
So the cause is bad driving. Not speed cameras.
Re:How to resorb a traffic jam (Score:2)
Re:How to resorb a traffic jam (Score:2)
What is shocking is that so many people seem to forget it the monent they get their license.
Re:WOW --- Just What we Need (Score:3, Interesting)
Re:The correct city driving speed (Score:3, Insightful)