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Chaos and Your Everyday Traffic Jam

Posted by timothy on from the could-often-be-my-dad's-nutty-driving dept.

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?"

56 of 477 comments (clear)

  1. Passion of Traffic by P(0)(!P(k)+P(k+1)) · · Score: 5, Funny

    From TFA:

    So the next time you find yourself stuck in bumper to bumper traffic, it's very possible that the jackass that caused it is already at home watching the latest episode of American Idol[...].

    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.

  2. Site jammed up by johnw · · Score: 4, Funny

    Only three comments and already the site seems to have been totally jammed up by a single Slashdot article in too much of a hurry.

  3. I know, I know!! by quokkapox · · Score: 5, Insightful

    "What causes these mysterious traffic jams that continually appear throughout the day for no reason whatsoever?

    Too many cars?

    --
    it's a blue bright blue Saturday hey hey
    1. Re:I know, I know!! by iangoldby · · Score: 2, Interesting
      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?

      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...
    2. Re:I know, I know!! by SpinyManiac · · Score: 2, Insightful

      I'm guessing here, but I'd say it's a large amount of traffic in a small area. I've seen it happen on motorways (typically three lanes in each direction) when a truck overtakes another one very slowly and all the cars pile up in the other lane. Everything behind is forced to slow down and the congestion propagates back up the road behind them.

      --
      It's never too late to have a happy childhood.
    3. Re:I know, I know!! by dajak · · Score: 2, Interesting

      Sometimes creating a new traffic jam will relieve pressure somewhere more important downstream, making the road network as a whole more efficient. Sometimes even closing lanes works.

    4. Re:I know, I know!! by UbuntuDupe · · Score: 2, Interesting

      Good (if obvious) point. A traffic jam can be caused by too many cars, by stupid drivers, or by both. For example, if a high capacity road has to "dump its load" onto an intersection with a traffic light, the traffic will still back up, regardless of the mental abilities of the drivers. On the other hand, I've seen traffic back up, even when the freeway is well below capacity, simply because of the right combination of stupid drivers. Such as when the two people in the middle and outer lanes decide to drive the same speed, creating an impassible wall, and the driver in the inner lane decides it's his GOD-GIVEN INALIENABLE RIGHT to drive whatever speed he damn well pleases in that lane, even if he's just going to camp there.

      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.

      --
      Apology to Ubuntu forum.
  4. Field of Study by WaXHeLL · · Score: 4, Informative

    There's actually a field of study for this: Traffic Analysis. Of course, this is not to be confused with all of the material out there relating to internet/network/packet analysis.

    This mainly deals with optimizing freeways and the like, based on people's behavior in traffic, and the ripple affects.

    --
    The troll with karma.
    1. Re:Field of Study by micheas · · Score: 2, Interesting
      . . . 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.

      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.
      --
      Work bio at MMWD
  5. Roads and CSMA/CD by rar42 · · Score: 5, Insightful
    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 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.

    --
    rgds,
    Richard Rothwell
    "All that is required for evil to triumph is that the good keep silent"
    1. Re:Roads and CSMA/CD by DynaSoar · · Score: 5, Interesting

      rar42 (626382) sez:
      > 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.

      --
      "I may be synthetic, but I'm not stupid." -- Bishop 341-B
    2. Re:Roads and CSMA/CD by LainTouko · · Score: 3, Informative

      90% of drivers are below average drivers.

      thats a funny average.

      It would be a funny median. Perfectly sensible mean or mode though.
    3. Re:Roads and CSMA/CD by siride · · Score: 2, Informative

      It's actually 1/35th of a mile. Think about it. One second at 70 mph is 1/70th of a mile, so two seconds is 2/70ths of a mile or 1/35 of a mile.

    4. Re:Roads and CSMA/CD by Dread_ed · · Score: 2, Interesting

      "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."

      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.

      --
      When the only tool you have is a claw hammer every problem starts to look like the back of someone's skull.
  6. On a very busy road... by Alioth · · Score: 5, Interesting

    I fly light planes. Major roads, when VFR, are very good landmarks.

    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 ... then the drivers behind (probably following far too close) brake a bit harder, and the drivers behind them brake a bit harder still. The adjacent lanes, in seeing one lane suddenly slow go 'whoa', and someone also brakes in that lane. Pretty soon, just from one person braking a little bit - the braking has propagated down the road with greater and greater severity until one of two things happens: usually, the traffic comes to a standstill, and you get a self-sustaining standing wave of stopped traffic until the amount of traffic on the road reduces to the extent there are fewer cars joining the wave than are leaving. This can take HOURS, especially on the M6 in England. The second thing that may happen in this cascading braking severity is that someone runs into the back of the other. Then chaos ensues for most of the day.

    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.

    --
    Oolite: Elite-like game. For Mac, Linux and Windows
    1. Re:On a very busy road... by RotateLeftByte · · Score: 5, Interesting

      Some of the points are very well made.
      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.

      --
      I'd rather be riding my '63 Triumph T120.
    2. Re:On a very busy road... by steevc · · Score: 3, Interesting

      It would help to cut down on the standing waves if people applied the 'join slowly, leave quickly' rule. If you see a queue ahead then slow down to give it time to move before you get there, then as soon as the road is clear accelerate away (to a safe speed). I see waves like this every day and see many people rush to join it so they have to slam on the brakes. When I get out the other side people are leaving huge gaps that slow down the escape of others.

      There's an old article on this, with animations, here.

      Try and be part of the solution.

    3. Re:On a very busy road... by Alioth · · Score: 4, Insightful

      Oh, I do that. The thing that annoys me is when I see trouble ahead and start to slow, as soon as the tiniest gap opens, someone in an adjacent lane leaps in. It's so frustrating. Many of the problems are caused by poor 'me first' road discipline, for example, when approaching a constriction, so many drivers go right to the end and try and force their way in - and it's not helped by people not letting adjacent lanes merge in good time before the obstruction.

      The art of proper merging should be something taught to drivers and tested on the driving test.

      --
      Oolite: Elite-like game. For Mac, Linux and Windows
    4. Re:On a very busy road... by MaelstromX · · Score: 4, Interesting

      That article is a must-read. Also interesting is this Java traffic simulator which demonstrates all the ways that traffic jams can form.

      --
      audioLibre - freedom of music
    5. Re:On a very busy road... by mrchaotica · · Score: 3, Interesting
      for example, when approaching a constriction, so many drivers go right to the end and try and force their way in - and it's not helped by people not letting adjacent lanes merge in good time before the obstruction.

      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.

      --

      "[Regarding the 'cloud,'] ownership was what made America different than Russia." -- Woz

    6. Re:On a very busy road... by berj · · Score: 2, Insightful

      Umm. you may want to *read* the article at http://amasci.com/amateur/traffic/traffic1.html (posted earlier). His evidence suggests that it *is* helped by people letting others in (in an effort to keep traffic flowing) and is actually *hindered* by behaviour such as yours.

    7. Re:On a very busy road... by Scratch-O-Matic · · Score: 2, Interesting

      Sometimes you can tell the difference. On my commute home every day there is a one-lane offramp with a stop light at the top, and it gets backed up a half mile or so. As I approach the final merge point, most drivers who are still trying to get in have arrived at full cruising speed...an obvious attempt to "cut in line." I will ride the bumper of the car in front of me like I was on his trailer hitch to keep these jerks out. Other times, usually much further back, drivers are trying to get in late but have obviously made a good faith effort...I let these in when able.

      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.

      --


      Evil is the money of root.
    8. Re:On a very busy road... by Skater · · Score: 4, Informative

      Uh, merging in at the end is exactly what they SHOULD be doing. Think of it as a "zipper" that closes at the end of the lane. It works out better for people in both lanes. The people that merge in early actually make the continuing lane slower for everyone.

  7. Those damn butterflies are attacking America again by giafly · · Score: 3, Funny
    From the article: "The 'butterfly effect' leads to a conclusion that if a butterfly flaps its wings ... that small disturbance in the chaotic motion of the atmosphere could create a chain reaction"
    America doesn't need a war on terror, it needs a war on butterflies.
    --
    Reduce, reuse, cycle
  8. slow ass drivers by mrshowtime · · Score: 3, Interesting

    I have lived in the cities with the worst drivers and the worst traffic and I have seen it time and time again; it's the slow dumbasses that are the real cause of majority of wrecks. It's that asshole who is going 50 in the passing lane and won't move. Or the driver is just going so slow that normal traffic rams into him, or is slowed town greatly.

    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.

    --
    "Jeremy, you need to get to an internet cafe and cut and paste some appropriate sentiments about me from the world wide
    1. Re:slow ass drivers by dbIII · · Score: 2, Insightful
      it's the slow dumbasses that are the real cause of majority of wrecks. It's that asshole who is going 50 in the passing lane and won't move.

      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.

    2. Re:slow ass drivers by beelsebob · · Score: 4, Insightful
      I'd agree with you partially, slow drivers getting in the way is a major cause here. But I'd suggest that it's usually actually the person in the expensive powerful car being impatient that causes the major tail backs.

      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.

    3. Re:slow ass drivers by Lumpy · · Score: 2, Insightful

      REally? I always saw the asshole on the pocket rocket driving in between lanes at 120mph that eats a car or two that causes most of the problems. At very least he causes the panic-able drivers to hit their brakes when a moron flies past their door 8 inches away. The slower drivers rarely cause the traffic jams it's the guys that flip out and then cut off other people because they think they are more important and thus have the right to tailgate, drive 20-30mph over the speed limit and have a little kid hissy fit when they encounter a slower driver and then start their childish behaivoir all over again causing others to have to jam on brakes, etc....

      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.

      --
      Do not look at laser with remaining good eye.
    4. Re:slow ass drivers by dbIII · · Score: 2, Insightful
      Come on - you learned to stop in time when a car brakes in front of you to get your licence. Stopping in time for a car in front of you that you can see is the easy bit - it doesn't matter if they do something stupid, annoying or illegal if you are too close it is your body that can get injured so it is your own responsiblity to pay attention. Let one idiot sit in front of you being a pain instead of having two dead idiots. Cars come with horns and lights but not a battering ram even though some people drive as if they do.

      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.

    5. Re:slow ass drivers by Overzeetop · · Score: 2, Informative

      Well, since the OP is in LA (from the freeways he listed) - I would presume the legal limit is 65 (mph, that is), but the "free flow" of traffic is likely to be closer to 80-85 if there are no other obstructions. So, in reality the 50 the OP mentioned is probably more like 65 - practically standing still by LA standards.

      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.

      --
      Is it just my observation, or are there way too many stupid people in the world?
    6. Re:slow ass drivers by tuskentower · · Score: 2, Insightful

      there's someone driving at a sane speed

      Don't take this the wrong way, but you just said what the guy/gal driving at 60mph (10 mph under the speed limit btw) thinks of you. They see the limit as the maximum, not the minimum. You should extend the same courtesy to the person driving 100mph that you would like to see from the person driving 60mph. Don't call him selfish just because drives faster than you. Maybe s/he shouldn't tail gate you, maybe s/he should. It's up to you not to give that person the opportunity to tail gate you.

      The key here is to pass fast. For example, my cruising speed is 10-15mph + speed limit, but I pass somewhere between crusing speed and 90mph (depending how fast that person charging down the passing lane is going). When you pass fast you achieve passing speed before you enter the next lane to pass. If you are unwilling to achieve the speed to pass fast, don't attempt to pass.

  9. Isn't it fairly obvious? by eebra82 · · Score: 2, Insightful

    Isn't it fairly obvious why we get traffic jam?

    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.

    --
    Full Tilt
  10. How to help unjam and jam by weave · · Score: 3, Insightful

    This is why when in a jam the best thing for people to do is calm down and change their speed slowly to even out the speed. This means trying to predict the average speed ahead of you and do your best to maintain an even speed, even if slow. Yes, impatient drivers will move in in front of you, but they are also most likely to jump back out of in front of you in a bit too. Getting next to a truck doing the same thing helps. Pressing out the waves is what will get traffic moving again for those behind you.

    1. Re:How to help unjam and jam by Keeper · · Score: 2, Insightful

      You can even turn it into a bit of a game ... see how far you can travel without touching the brake.

      A few other beneficial side effects:
      * better gas mileage
      * less stress
      * less wear and tear on your brakes

  11. Density waves? by niktemadur · · Score: 3, Interesting

    The previous theory I heard about in a documentary about traffic in major cities, said that density waves, the same phenomenon that causes many galaxies to have perfectly defined spiral arms, also cause traffic jams, which is to say, the mathematics are the same.

    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.

    --
    Lil' Thindime, lilting a lacrimose lament, krashes the kwaint konfines of Kokonino Kounty
  12. Re:Where I live ... by Patrik_AKA_RedX · · Score: 5, Funny
    I've nearly forgotten what traffic jams are like.
    It's like waiting in front of a traffic light. Except there are no lights, especialy no green ones. And a lot of people can't make up their mind about which direction they'll take after the lights and switch lanes accordenly.
    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 ... with sound!
    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.
  13. It's too obvious by arikb · · Score: 5, Funny

    For the longest time a friend and I have theorized about the reasons for those traffic jams. We've reached the inescapable conclusion that they are the results of a conspiracy.

    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

  14. Old, old, incredibly old news by deblau · · Score: 5, Interesting

    See this Science Hobbyist article from January 1998. It's long and detailed, and suggests practical steps individual drivers can take for breaking up (or causing!) traffic jams. Yes, dear readers, this is a nine-year-old dupe.

    --
    This post expresses my opinion, not that of my employer. And yes, IAAL.
  15. Re:Where I live ... by aussie_a · · Score: 2, Funny

    Around here, the closest thing to a traffic jam is me. Even the old people think I drive too slow. Wow, that must be pretty embarrassing considering you live in an Amish community.
  16. Valid reason, but not the main one by mapkinase · · Score: 3, Interesting

    I can testify that this is not the most popular reason of traffic jam, because this is not the most common disruptive behavior. Think: why the situation was happening? It is not because just one driver wanted to change the lane, this is because many drivers wanted to do that and one of them was too impatient. That takes off the load of one individual and brings it upon the condition of why the lane was slow?

    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.

    --
    I do not believe in karma. "Funny"=-6. Do good and forbid evil. Yours, Oft-Offtopic Flamebaiting Troll.
  17. Re:It's both! by zero_offset · · Score: 5, Interesting

    The two-second gap is typically recommended for 70 MPH speeds. It is dramatically smaller for lower speeds. It is also completely unrealistic at any speed. A two-second gap at 70 MPH is about 315 feet, or about 24 car lengths. At 70 MPH the assumption is that the average person requires about 2/5th of a second to react, which equates to just under 70 feet. That leaves 247 feet for braking. The NHSTA pegs the average 70 MPH braking distance for modern cars around 170 feet. I personally suspect it's much lower these days, and with panic braking plus ABS it would be far, far lower. But give them the benefit of the doubt (though god only knows why) and call it 160 feet. That leaves you 87 feet, so the two-second gap is overly conservative by a factor of about 25%.

    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 ... 16 cars per mile and the highway would look positively empty.

    --

    Slashdot quality declines as the number of hot grits posts decreases. - Provolt's Law, Apr-09-2005

  18. Despite kicking and screaming... by MsGeek · · Score: 2, Interesting

    ...light rail is working in Los Angeles. What's the fastest way to get Downtown? The Red Line. 30 minutes from NoHo to Union Station. Un-freaking-believable.

    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.

    --
    Knowledge is power. Knowledge shared is power multiplied.
  19. Re:WOW --- Just What we Need by zero_offset · · Score: 2, Interesting

    You were unfairly modded as a Troll, but you're absolutely right. I especially enjoyed the technical-looking but uncaptioned and completely-ignored graphics which accompanied the article.

    --

    Slashdot quality declines as the number of hot grits posts decreases. - Provolt's Law, Apr-09-2005

  20. Re:It's both! by aderuwe · · Score: 4, Insightful

    Different issue.

    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.

  21. Re:It's both! by at_18 · · Score: 3, Informative

    You are way too optimistic. Accidents don't happen when drivers are paying attention to what they are doing. Even when you aren't paying attention, most of the time nothing happens. Most accidents are the result of failing to plan for the worst case, which every now and then it does happen.

    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.

  22. Specific to Albany, NY area by Phreakiture · · 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 (along with some Google wierdness in the construction of the image).

    --
    www.wavefront-av.com
    1. Re:Specific to Albany, NY area by Stele · · Score: 2, Funny

      The construct that causes all of this trouble can be seen here (along with some Google wierdness in the construction of the image).

      I looked this morning and there was barely any traffic! I think you're exaggerating.

    2. Re:Specific to Albany, NY area by malfunct · · Score: 4, Interesting

      A better solution is to strictly enforce following distance laws. A study was done on traffic patterns in Seattle area to see how they could be improved and found that the single most important thing to fix the issue was to give proper following distance between cars. This counteracts the pipeline bubbles (yes almost the same thing as a bubble in your processor pipeline) by giving room to absorb sudden stops and also solves some of the merging issues that we see. Its more likely than not that even though the one jackass that was spoken about in the summary triggered the slowdown the real cause was everyone crowding the person in front of them so that the sudden stop was propogated in perpetuity instead of being absorbed and spread across the whole flow.

      --

      "You can now flame me, I am full of love,"

  23. Re:It's both! by zero_offset · · Score: 3, Insightful

    If we planned for the worst case, driving would be illegal. :)

    --

    Slashdot quality declines as the number of hot grits posts decreases. - Provolt's Law, Apr-09-2005

  24. Seriously. by aussersterne · · Score: 2, Insightful

    Everybody is busy pointing out the "first causes" of traffic jams without noticing that every one of these causes is caused by interaction with the roads in the first place.

    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.

    --
    STOP . AMERICA . NOW
  25. Re:The correct city driving speed by zero_offset · · Score: 2, Insightful

    I also notice that the cyclists tend to take a rather liberal view of their obligation to obey traffic control devices. If you scaled the available road space down and traffic levels up, cyclists would have just as much trouble. The only reason they don't is because we build roads for cars, then we allow bicycles to use them.

    --

    Slashdot quality declines as the number of hot grits posts decreases. - Provolt's Law, Apr-09-2005

  26. Re:It's both! by An+ominous+Cow+art · · Score: 2, Informative

    Your numbers are a bit screwy. 70mph = 102.67fps, so a 2-second gap is about 205ft.

  27. Mod parent up by Razed+By+TV · · Score: 2, Insightful

    Nice find.

    So a 2 second gap is 205 feet.
    2/5ths of a second then equates to 41 feet.
    That leaves 205 - 41 = 164 feet left to stop, which is 6 feet less than the number cited for the average modern vehicle to stop. So the two second rule is deficient by about 3.5% for the average modern vehicle.
    On a side note, modern isn't exactly defined, but I don't think my '87 station wagon (with no ABS) qualifies.

  28. Re:It's both! by ukemike · · Score: 2, Interesting

    but it certainly doesn't equate to a 70MPH-to-zero panic stop in a limited space.


    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.
    --
    -- QED
  29. Re:It's both! by Gr8Apes · · Score: 2, Insightful

    Actually, it's the fault of the moron that left his car in the road, most times. I've never figured out why a car is left in the lane, especially in an open road. I've seen this more than once, and almost hit an abandoned car in the left lane once with a perfectly available shoulder right next to it.

    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.

    --
    The cesspool just got a check and balance.
  30. Re:Lane merges by orgelspieler · · Score: 3, Insightful
    here's what I do: I drive in the closing lane, but only as fast as the person next to me (normally pretty slow). That way, the guy next to me doesn't think I'm "a cutter" and keep me from getting in when the time comes. Of course there's some idiot flashing his brights and honking, and doing sign language, because there's all this "open space" ahead of me. But it's only open for a quarter mile, and I'm not gonna let that idiot cut in front of all the other nice people who are trying to do the right thing. If he does, everybody will have to slam on their brakes and let him in.

    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.