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Traffic Experiments -- How to clear traffic jams

115 points by cubix 16y ago

daten 16y ago
The success of this technique can't be accurately measured by the driver who's trying "smooth" out the waves. It needs to be witnessed from outside of traffic. It usually just moves the problem to behind the "helpful" driver as other drivers can very easily continue to drive competitively and recreate the effect. Even if he's successful in removing the "wave", it's just by decreasing the average speed of traffic. Please don't try this in the left lane.
- keyle 16y ago
  That's exactly why nobody would play along even if they knew. Big trucks eventually do that because it's painful for them to do the gears 1,2,3 constantly, they stay in second or third and just slow down the whole thing. Here is the thing where it falls short though: the guy at the front riding the wave really slow to "help lane locks" will also get merging traffic many many time right in front of him (people taking advantage of the free space), as a result, it won't help that lane but only make it worse if you're stuck behind such driver (or truck). So if everyone stuck to their lanes, didn't change unless extremely necessary, and played the wave-canceling technique, it would work. In other words, this will work when cars will be driven by computers hooked together via apis and maybe a traffic controller. I'm not signing for the beta.
  - maushu 16y ago
    Yeah, I always thought that the only way to prevent traffic jams would be to remove the human factor entirely. Makes me wonder why people fight so much against this, I would love to be able to read while going to work (when I don't catch the bus as usual).
    - daten 16y ago
      I would love seeing fewer drivers in cars already reading on their way to work. Educating human drivers may be just as good as replacing them.
  - zepolen 16y ago
    Actually, the fact that people in the middle lane are taking up his 'free' space helps the long term traffic. The main cause of traffic wave is from someone stopping too abruptly, eg. if someone changes lane in tight traffic, he forces the other person to slow down too fast, which begins the wave. If you allow more people to get in front of you in a smooth manner because you have given yourself a lot of distance, then there will be less 'cutting off' slow downs from the middle lane guys, which in turn causes less cutting offs in the right lane. How much does it hurt over your entire commute to let even 100 cars in front of you? You'll be 500 meters later to your destination, what's that at 30kph...1 minute more? That's the worst case scenario. The normal case is you'll get there quicker because you've raised the average speed of the entire traffic wave.
    - superk 16y ago
      Absolutely! I've thought about this so many times... what is 5 seconds for you (allowing someone to merge in front of you) would translate to much much faster commute to _everyone_ else. It is all about the balance between my personal greed and what's better for the common good (if only we could solve this on _and_ off the road). Where I live there is terrible traffic... and I've contemplated causes and solutions many a mind-numbing commute. I realized we behave differently when we are behind the wheel... Very few people would behave or maneuver the same if it where lines of people instead of cars. That is why your best chance to merge is to make eye contact with the other driver - if they recognize you as another human not just another vehicle than they are much more likely to move over or make space. When I drive (during rush hour) I suffer a lot to justify my actions. What I have settled on... is a simple rule: In any situation the person who is in the wrong is the one who has contributed to the impediment of the overall flow of traffic. This comes back to what zepolen says (and I agree with). If we could ever make the connection that what's good for my fellow (wo)man is good for me too... we would be so much better off in general.
      - daten 16y ago
        I agree in the situation where all other drives on the road are equally intelligent and paying attention when they drive. Sadly, in the area I drive in, many drivers are constantly paying more attention to their phone than the road. Those drivers cause all of the traffic problems I see. They likely contribute to many of the accidents as well. They will end up leaving huge gaps in front of them at the expense of traffic behind them even when traffic ahead of them is moving smoothly and quickly. The cost of letting cell phone drivers in front of you can be many minutes to your commute per each driver. Add a few minutes for each traffic light or merge lane that you will spend behind the inattentive drivers. In a 5 mile commute, following the flow of inattentive drivers can add 45 minutes to my drive. Attentive driving and following the flow of other "aggressive" drivers can make it a 10 minute drive total. So what I have actually found helps, in a real world scenario, not a fictional one where all drivers are equal, is trying to identify and cooperate with other "aggressive" drivers helps the group of aggressive drivers get through traffic efficiently and gives the cell-phone drivers plenty of time to concentrate on their conversations.
- lars512 16y ago
  Actually, if the wave is successfully removed average traffic speed should increase. In fact, the whole post is an argument about ways to improve average traffic speeds. He basically advocates estimating how fast traffic is really going, and going at that speed. Instead of reaching a bottleneck quickly, you should slow down appropriately in advance so that you never have to actually stop. Note that you (and the people behind you) still get through the bottleneck at the same speed, so there is no cost to you (or them), just less braking and accelerating. For what it's worth, some freeway entrances near me (Melbourne, Australia) have traffic lights which rate-limit entry onto the freeway in peak hours. This is exactly the same as what this author is trying to do; by rate-limiting cars at entry, they're not actually slowing them down, since it increases average on-freeway speeds.
  - deleted 16y ago
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- ergo98 16y ago
  I'm not sure if you really got the point of the article: The wave happens because everyone wants to be {X} behind the person in front (usually because they desperately want to block anyone else getting between them and {X}). If you can enforce (for lack of a better word) a constant speed, people can maintain that {X} distance without constant accelerating and braking -- just by coasting at a constant speed. >Even if he's successful in removing the "wave", it's just by decreasing the average speed of traffic. How would it decrease the average speed in any practical way? Secondly, it would dramatically reduce the energy consumption of the waves (accelerating and braking constantly) and wear and tear on vehicles. The net benefit of optimizing highway traffic -- in real environmental and economic benefits -- is significant. >Please don't try this in the left lane. The left lane has no meaning during congestion. There is no "passing" when the highway is clogged. And yes, this is actually the law in many places. One of the biggest causes of highway inefficiency are the self-important (but usually going nowhere) people who pretend that by driving aggressively, they should be allowed through the congestion.
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Sukotto 16y ago
An oldie, but a goodie. I base my commuting style on this guys articles. Drive slightly slower than everyone else and let large spaces grow in front of your car. It's a lot harder than it sounds (for me anyway) but when I get it right, it makes my drive much more enjoyable. People that just HAVE to drive as fast as possible will go around you (you should never do this in the left lane) and everyone else will sort of get in line after you... it looks a bit like those nascar groups where all the cars go exactly the same speed.
- loewenskind 16y ago
  Except that people who want to go faster than you will pass you and get in front of you. This leads you to either keep slowing down to maintain the space or start shrinking the space.
  - Sukotto 16y ago
    Yes, many people will pass you and go in front. That's not such a big deal since many of them switch into yet another lane (Some will even exit the freeway only to immediately re-enter) as they try to gain even half a car-length on everyone else. I don't feel like competing with them. Personally, I'm not trying to fix traffic for everyone. I'm selfishly trying to make my own commute as pleasant as possible. By following the advice in this old article I've managed to greatly improve my own drive, and I find the amount of time I spend in the slow pockets of traffic greatly reduced.
    - daten 16y ago
      I'm concerned that when cars doing this are the minority, with other traffic constantly going around them, they just become an obstacle in traffic. If you inspire other cars to change lanes to pass you, because you're intentionally driving slower, you may be making traffic less safe.
      - travisp 16y ago
        Except that by doing this you can (in theory) make traffic actually move faster, so there will ultimately be less passing.
chopsueyar 16y ago
Old.
- daten 16y ago
  He's right, this has been posted on HN before. I seam to remember the old article having more animated illustrations. I don't know if it's the same page, same author or just similar content.
  - Kliment 16y ago
    The animations are linked at the bottom of the article.
DanielStraight 16y ago
The solution to traffic jams is to not leave transportation in the hands of clueless, distracted, reckless drivers. The solution is fast, reliable, ubiquitous public transit.
- stefs 16y ago
  or jetpacks!
  - nphase 16y ago
    or teleportation devices
- nradov 16y ago
  Public transit is impractical and uneconomic in many areas. The real solution is smart roads and computer-driven electric cars.
  - rbranson 16y ago
    Perhaps, but in the context of the article, traffic jams only exist because of commuters. The interstate & highway systems were not designed for commuters and should not be used for them. While I think computer-driven cars will be a boon to the environment and economy, the capital investment needed is pretty fantastic, which is going to be some decades off. In fact, a real solution to this problem that could be applied in the design of our current urban landscape would be a multi-pronged effort to spread out the commuter traffic. Alternating work and school hours could widen commuting hours and distribute load across all commuter infrastructure. Increased levels of telecommuting would also contribute to this. This would be a sort of supply-side fix to commuter congestion. Local or regional governments could create incentives to encourage these changes.
    - nradov 16y ago
      The first-generation interstate highway system wasn't designed for commuters, but everything added or upgraded in the past 40 years has been. Many new luxury cars already come with limited computer driving, in the form of adaptive cruise control. The capital investment is small and rapidly dropping, and just that one innovation could deliver a major reduction in traffic congestion. http://www.springerlink.com/content/p56714553g82r2h7/ http://www.springerlink.com/content/p56714553g82r2h7/
fbnt 16y ago
Maybe the author never heard anything about green waves. http://en.wikipedia.org/wiki/Green_wave http://en.wikipedia.org/wiki/Green_wave
- superk 16y ago
  Green waves are a pet peeve of mine. They've tried to implement these where I lieve... a spectacular failure. Green waves only work when there is NO traffic. Speed is regulated and the flow moves fine. During rush hour they are a disaster. Every light is backed up to previous. My light turns green, then I have to wait 10 seconds for the next light to turn green and the entire line of traffic to move, before I can advance. This usually results in a stop at each light. A much better solution is what I remember from NYC: all the lights turn green at once, all the traffic moves.
ritonlajoie 16y ago
In northern America, I think most of the cars have automatic transmission. In France, (where I live), we mostly (maybe 99% ?) have manual transmissions. Have you ever experimented a traffic jam with a manual trans. car ? You have to switch gears every 10 seconds and it's very very very annoying. I'm telling you that, because as a frequent driver (well, today I drive a bike but still) in Paris, and kind of very observant, I clearly see that most people are not doing what these drivers do in this experiment. Most of the time, everybody will let a huge space between the car behind them in order to avoid changing the gears too frequently. On the contrary, on automatic cars (I had one and drove another for 6 months in Canada), that's easier to go & stop & go & stop & go & stop, etc... Not sure if it's related, but I think it is, in a small proportion. edit: my english
- maw 16y ago
  Pretty sure transmission type has nothing to do with it -- traffic is stop and go in plenty of places where most cars have manual transmissions. I'm increasingly convinced that it's due to so many drivers optimizing for local minima, at the expense of not just everyone around them, but of themselves thirty seconds later.
  - maw 16y ago
    Duh, I meant local maxima, of course -- at least, that's what those drivers are trying for. What they get most of the time are more like minima, of course.
- vaksel 16y ago
  why exactly do you need to switch gears? Just leave it in first. And engage the clutch when you are stopped.
  - daten 16y ago
    If you're stuck in traffic for a long time, your leg engaging the clutch can get very tired. So you're constantly switching to neutral to rest your leg. It's also not uncommon for traffic to go from stopped, to fast enough to warrant 2nd gear, back to stopped.
daychilde 16y ago
I had the good fortune to do a three month internship in Seattle last spring. And I have to say - after growing up in Dallas, now living in Florida, and seeing traffic in other places... Seattle drivers are unique. I've seen this [appear to] work in Seattle. While I was there, I tried it, and it appeared to work. However, while I lived in Dallas, I was aware of this idea, and tried it there - and no way. People cut in, people tailgated - it completely doesn't work. So I think it partially depends on the nature of the city's drivers. And there is something special about Seattle.
- daten 16y ago
  I live and work in DC. I go to Dallas at least once a year and drive every day during the week and weekend. I agree this would be impossible in Dallas traffic. It doesn't feel as intentionally aggressive as DC traffic, instead it's like everyone in Dallas can't take their foot off the accelerator even if they wanted to. It's hard enough finding a space between two cars to merge, you usually have to just go for it and hope the rear car can find his brakes.
  - daychilde 16y ago
    It definitely took me a while after moving away from Dallas to change some of my driving habits. I still definitely change lanes more than most drivers around here - although I do my best not to cut anyone off, and I actually let drivers in here... something definitely not done often in Dallas. It also helps that I went from a 90 minute commute (each way) to usually a 10-15 minute commute here (depending on where I've worked). Smaller towns do have some benefits...
stuaxo 16y ago
Thats what those changable speed limit signs on the motorway are trying to achieve. (I've also seen markings to keep cars 10 metres apart on some roads).
Luc 16y ago
Where I live there's something called 'block driving' (I haven't found a better translation for the Dutch word 'blokrijden'). On busy summer days, when the highway to the coast is jammed, a police car will block the highway, then drive at a constant speed (and slower than the maximum speed), with no one being allowed to pass the police car. Apparently this helps to resolve the traffic waves.
- superk 16y ago
  That's actually one of the solutions suggested by the author. A rolling blockcade of police cars in each lane to regulate the flow.
- 0x5a177 16y ago
  The California Highway Patrol appears to do this in Southern California as well. I've seen a patrol car start weaving between two lanes, then three, weaving more and more until it's blocking all lanes of traffic like a weavy pace car.
  - mds 16y ago
    They do that to slow or stop traffic when there's debris or an accident ahead.
  - bmm6o 16y ago
    It's called "running a break", and I've only seen it used to clear debris or disabled cars out of lanes, or so that a construction crew can close a lane. It'll freak you out the first time a cop car swerves in front of you across 5 lanes of traffic.
    - davidu 16y ago
      I've definitely seen it used in both Nor Cal and So Cal to slow traffic down. They do it on I-5 fairly often during rush hour, of all times.
CaptainDecisive 16y ago
Interesting observation is that what TFA calls the "cheaters", ie those who drive to the end of their lane before merging at the last minute, may actually be doing the right thing. See Tom Vanderbilt talk about it here http://www.vimeo.com/6779064 http://www.vimeo.com/6779064. If you're interested in this there's a nice longer interview with Tom at Streetfilms http://www.streetfilms.org/tom-vanderbilt-talks-traffic http://www.streetfilms.org/tom-vanderbilt-talks-traffic or an hour long Google talk.
- ajb 16y ago
  He doesn't say why in the short one (I haven't watched the long one). Late mergers are definitely bad in some situations - for example, when they are merging into a slow-moving turnoff lane, blocking a whole lane of ongoing traffic.
  - CaptainDecisive 16y ago
    He goes into the research a bit more in the Google talk and you see where he pulls the magic "15% improvement" from. Also he has a book (which I haven't read) called Traffic so he might explain it more or cite studies there. I agree though that it doesn't really work in all situations. Tom uses the example of two lanes merging into one for roadworks. Maybe some situations where it doesn't work are an example of poor road design by traffic engineers?
mootothemax 16y ago
Heh, I didn't realise that it had such an effect, but this is the exact same game I play when caught up in a heavy traffic: the how-long-can-I-go-before-breaking game! ;-) It could be related to driving a manual and being lazy, but it helps your concentration no end :)
- Deestan 16y ago
  No idea why you were at -1; your comment was informative and on topic. On a side note, I also tend to play that "game" when stuck in slow home-from-holiday traffic over the mountains. Changing speeds all the time while driving manual is such a pain.
tomjen3 16y ago
The problem with slowing down miles in front of a traffic jam is that those who normally gets of before that space now has to suffer too. In addition, most people would cut you of if you drove slower than the maximum speed.
kostko 16y ago
I remember reading this article while back: "Traffic jam mystery solved by mathematicians". http://www.physorg.com/news117283969.html http://www.physorg.com/news117283969.html So now when I'm in a jam, I just slow down instead of engaging the speedup, break pattern. Haven't looked behind me though to see if I had any effect on the traffic behind me.
DanielN 16y ago
I've tried this in Boston. Mass-holes will not stand for you to screw with their traffic jams.
- cakeface 16y ago
  I agree that this doesn't work well around Boston. My opinion is that the fluidity of traffic, ie. lane changing, doesn't break down at low speeds in Boston. If you let a cars length open in front of you it will fill up with a car. I tend to think that this makes efficient use of the pavement available and tends for a traffic flow that is as maximal as possible but I don't have any evidence about that.
  - asmithmd1 16y ago
    If efficient use of pavement means park the most cars on it Then by all means fill every available space. Safe following distance increases with the square of the speed so higher average vehicle speeds means the road carries less traffic. The road moves the most cars around 30mph, so if traffic slows below 30 it will crash to 0mph
    - cakeface 16y ago
      Cool! What is the science backing this? Is it coming out of studies or some theoretical modeling? I've been wondering what the most efficient speed for moving traffic was on a typical highway for a while.
      - asmithmd1 16y ago
        When I don't know anything about a topic I have found Wikipedia is a good place to start http://en.wikipedia.org/wiki/Traffic_flow http://en.wikipedia.org/wiki/Traffic_flow
      - deleted 16y ago
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      - wbeaty 16y ago
bryanh 16y ago
So, what would happen on major interstates if highway patrols kept a steady pace? Is that a viable solution? Wouldn't they eventually run up on another wave of cars and ruin everything? I would be really interesting to see if this actually improved interstate bandwidth during rush hours. But even more interesting, I bet a good portion of drivers would get upset at the fact that there are huge, unused gaps. I wouldn't be surprised to hear from people who think it is grossly more inefficient than regular old traffic jams...
parallax7d 16y ago
I used to do this every once in a while. One thing to be aware of, are large trucks behind you at the top of hills. They tend to want to increase speed going down hills to use their velocity to climb the next. It's probably a good idea to accommodate this.
RyanMcGreal 16y ago
Yes, absolutely. This is my experience as well. Related: http://news.ycombinator.com/item?id=785498 http://news.ycombinator.com/item?id=785498
nwomack 16y ago
I've actually spent quite a bit of time pondering this. Here are my completely unscientific conclusions. Imagine a [moving] wall, on an interstate, moving at 30MPH. No matter what is happening behind this wall, it is impossible to maintain an average speed faster than the wall. You can try any amount of tricks to smooth out traffic, but it will be impossible to ever move past this wall. As long as there is a steady stream of traffic, no car will ever do more than 30MPH until this moving wall gets out of the way. So now let's, more realistically, replace the wall with a bunch of slow drives, and ask 2 important questions: 1. How to get out of this situation? -- We want these drivers to all SPEED UP! It's really as simple as this. Until these bottleneck drivers move out of the way, you can only smooth out traffic, but never increase the speed. 2. How to avoid this problem in the first place? -- In general, there will be some bottleneck. After too many cars are going through this bottleneck at once, there will be slowdown. Ideally, these bottlenecks should be identified and no more than the maximum amount of cars at a time should enter the bottleneck to decrease the speed of traffic. Of course, that's easier said than done, but I think the important thing to take away from my ramblings is this: The best way to get rid of a traffic jam is: if you are in the front of the pack and have a chance to accelerate, you should do so as quickly as possible. If everybody were to do this, average speed could then be increased.
- wbeaty 16y ago
  But note that there aren't any slowpokes here, instead, every single car is blocked by the car ahead of them. The people behind you think that you are the slowpoke driver. But nothing is blocking the traffic, instead the average speed of the long column of cars is determined by the spacing between cars, and that spacing is determined by psychology. In light traffic, some people go far faster than average, but nobody tries to stop them. When we arrive at heavy congestion, don't we suddenly decide to close up ranks to prevent aggressive drivers from passing, stop them from "cutting us off?" If everyone habitually blocks the speeders, then it means we've compressed the traffic pattern past the peak of maximum flow, and pushed it into the unstable realm of stop/go oscillations and standing waves or "ghost jams." Want jams to vanish? Then do as the pro truckers do and just freaking back off. Happily encourage other cars to merge ahead. (They're not "cutting you off," there's no such thing as "cutting you off." They're just trying to merge into the adjacent lane!) If traffic momentarily slows way down, everyone just make sure to keep an open space that allows merging, and you'll find that it speeds right back up again.
tobtoh 16y ago
In Melbourne, Australia, a similar concept was used to ease congestion entering freeways. We had a peak-hour problem where cars would flood the entry ramps, but struggle to merge with the existing freeway traffic - this caused people to brake/slow down which resulted in major jams. To alleviate this issue "there are traffic lights at some freeway entrances to control the flow of vehicles onto the freeway when the traffic is heavy. When operating, the lights will change quickly, so that when the light is green only one vehicle in each lane will be able to enter the freeway." (taken from VicRoads website) The lights basically cycle from red to green every 2 seconds. That's enough to regulate the flow onto the freeway and minmises jams on the entry ramp and at the merge point between the freeway and entry ramp.
- tobtoh 16y ago
  In fact, here is a YouTube video of the lights in operation: http://www.youtube.com/watch?v=YFrEd8qSVCc http://www.youtube.com/watch?v=YFrEd8qSVCc
- colonelxc 16y ago
  This is used extensively in the SF bay area.
alexyim 16y ago
A side effect of doing this is that it is much more fuel efficient to not have to go into a cycle of breaking and accelerating again.
drv 16y ago
Somewhat different from the commuter-oriented topic of the article, I've seen attempts by truckers to enforce a similar pattern in construction zones (traffic reduced by one or more lanes) on long stretches of highway: In a situation where one lane has to merge because it is closed in the distance, the "nice" drivers all merge far ahead of time, while the aggressive drivers attempt to go all the way to the end of the lane and then merge ahead of everyone, causing the kind of grinding gears described in the article. To combat this, a couple of big rigs driven in parallel in the open lane and the lane that is closed ahead block all traffic from passing. This prevents the aggressive drivers from attempting to merge at the last second, smoothing out the wave. I've seen this happen several times on cross-country trips; I wonder if the truckers coordinate over radio or just choose to do it independently. On a related note, I wonder if "lane closed ahead" signs placed too far ahead actually make this problem worse, since many drivers will immediately merge out of the closing lane far ahead of time, causing a wall of traffic if the front of the line has to slow down for aggressive last-second merges.
tectonic 16y ago
As a side note, I remember reading articles on this author's webpage almost 15 years ago. Some awesome stuff from a long-time netzen! http://amasci.com http://amasci.com

115 points by cubix 16y ago

daten 16y ago

The success of this technique can't be accurately measured by the driver who's trying "smooth" out the waves. It needs to be witnessed from outside of traffic. It usually just moves the problem to behind the "helpful" driver as other drivers can very easily continue to drive competitively and recreate the effect. Even if he's successful in removing the "wave", it's just by decreasing the average speed of traffic. Please don't try this in the left lane.

keyle 16y ago
That's exactly why nobody would play along even if they knew. Big trucks eventually do that because it's painful for them to do the gears 1,2,3 constantly, they stay in second or third and just slow down the whole thing. Here is the thing where it falls short though: the guy at the front riding the wave really slow to "help lane locks" will also get merging traffic many many time right in front of him (people taking advantage of the free space), as a result, it won't help that lane but only make it worse if you're stuck behind such driver (or truck). So if everyone stuck to their lanes, didn't change unless extremely necessary, and played the wave-canceling technique, it would work. In other words, this will work when cars will be driven by computers hooked together via apis and maybe a traffic controller. I'm not signing for the beta.
- maushu 16y ago
  Yeah, I always thought that the only way to prevent traffic jams would be to remove the human factor entirely. Makes me wonder why people fight so much against this, I would love to be able to read while going to work (when I don't catch the bus as usual).
  - daten 16y ago
    I would love seeing fewer drivers in cars already reading on their way to work. Educating human drivers may be just as good as replacing them.
- zepolen 16y ago
  Actually, the fact that people in the middle lane are taking up his 'free' space helps the long term traffic. The main cause of traffic wave is from someone stopping too abruptly, eg. if someone changes lane in tight traffic, he forces the other person to slow down too fast, which begins the wave. If you allow more people to get in front of you in a smooth manner because you have given yourself a lot of distance, then there will be less 'cutting off' slow downs from the middle lane guys, which in turn causes less cutting offs in the right lane. How much does it hurt over your entire commute to let even 100 cars in front of you? You'll be 500 meters later to your destination, what's that at 30kph...1 minute more? That's the worst case scenario. The normal case is you'll get there quicker because you've raised the average speed of the entire traffic wave.
  - superk 16y ago
    Absolutely! I've thought about this so many times... what is 5 seconds for you (allowing someone to merge in front of you) would translate to much much faster commute to _everyone_ else. It is all about the balance between my personal greed and what's better for the common good (if only we could solve this on _and_ off the road). Where I live there is terrible traffic... and I've contemplated causes and solutions many a mind-numbing commute. I realized we behave differently when we are behind the wheel... Very few people would behave or maneuver the same if it where lines of people instead of cars. That is why your best chance to merge is to make eye contact with the other driver - if they recognize you as another human not just another vehicle than they are much more likely to move over or make space. When I drive (during rush hour) I suffer a lot to justify my actions. What I have settled on... is a simple rule: In any situation the person who is in the wrong is the one who has contributed to the impediment of the overall flow of traffic. This comes back to what zepolen says (and I agree with). If we could ever make the connection that what's good for my fellow (wo)man is good for me too... we would be so much better off in general.
    - daten 16y ago
      I agree in the situation where all other drives on the road are equally intelligent and paying attention when they drive. Sadly, in the area I drive in, many drivers are constantly paying more attention to their phone than the road. Those drivers cause all of the traffic problems I see. They likely contribute to many of the accidents as well. They will end up leaving huge gaps in front of them at the expense of traffic behind them even when traffic ahead of them is moving smoothly and quickly. The cost of letting cell phone drivers in front of you can be many minutes to your commute per each driver. Add a few minutes for each traffic light or merge lane that you will spend behind the inattentive drivers. In a 5 mile commute, following the flow of inattentive drivers can add 45 minutes to my drive. Attentive driving and following the flow of other "aggressive" drivers can make it a 10 minute drive total. So what I have actually found helps, in a real world scenario, not a fictional one where all drivers are equal, is trying to identify and cooperate with other "aggressive" drivers helps the group of aggressive drivers get through traffic efficiently and gives the cell-phone drivers plenty of time to concentrate on their conversations.
lars512 16y ago
Actually, if the wave is successfully removed average traffic speed should increase. In fact, the whole post is an argument about ways to improve average traffic speeds. He basically advocates estimating how fast traffic is really going, and going at that speed. Instead of reaching a bottleneck quickly, you should slow down appropriately in advance so that you never have to actually stop. Note that you (and the people behind you) still get through the bottleneck at the same speed, so there is no cost to you (or them), just less braking and accelerating. For what it's worth, some freeway entrances near me (Melbourne, Australia) have traffic lights which rate-limit entry onto the freeway in peak hours. This is exactly the same as what this author is trying to do; by rate-limiting cars at entry, they're not actually slowing them down, since it increases average on-freeway speeds.
- deleted 16y ago
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ergo98 16y ago
I'm not sure if you really got the point of the article: The wave happens because everyone wants to be {X} behind the person in front (usually because they desperately want to block anyone else getting between them and {X}). If you can enforce (for lack of a better word) a constant speed, people can maintain that {X} distance without constant accelerating and braking -- just by coasting at a constant speed. >Even if he's successful in removing the "wave", it's just by decreasing the average speed of traffic. How would it decrease the average speed in any practical way? Secondly, it would dramatically reduce the energy consumption of the waves (accelerating and braking constantly) and wear and tear on vehicles. The net benefit of optimizing highway traffic -- in real environmental and economic benefits -- is significant. >Please don't try this in the left lane. The left lane has no meaning during congestion. There is no "passing" when the highway is clogged. And yes, this is actually the law in many places. One of the biggest causes of highway inefficiency are the self-important (but usually going nowhere) people who pretend that by driving aggressively, they should be allowed through the congestion.

deleted 16y ago

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Sukotto 16y ago

An oldie, but a goodie. I base my commuting style on this guys articles. Drive slightly slower than everyone else and let large spaces grow in front of your car. It's a lot harder than it sounds (for me anyway) but when I get it right, it makes my drive much more enjoyable. People that just HAVE to drive as fast as possible will go around you (you should never do this in the left lane) and everyone else will sort of get in line after you... it looks a bit like those nascar groups where all the cars go exactly the same speed.

loewenskind 16y ago
Except that people who want to go faster than you will pass you and get in front of you. This leads you to either keep slowing down to maintain the space or start shrinking the space.
- Sukotto 16y ago
  Yes, many people will pass you and go in front. That's not such a big deal since many of them switch into yet another lane (Some will even exit the freeway only to immediately re-enter) as they try to gain even half a car-length on everyone else. I don't feel like competing with them. Personally, I'm not trying to fix traffic for everyone. I'm selfishly trying to make my own commute as pleasant as possible. By following the advice in this old article I've managed to greatly improve my own drive, and I find the amount of time I spend in the slow pockets of traffic greatly reduced.
  - daten 16y ago
    I'm concerned that when cars doing this are the minority, with other traffic constantly going around them, they just become an obstacle in traffic. If you inspire other cars to change lanes to pass you, because you're intentionally driving slower, you may be making traffic less safe.
    - travisp 16y ago
      Except that by doing this you can (in theory) make traffic actually move faster, so there will ultimately be less passing.

chopsueyar 16y ago

Old.

daten 16y ago
He's right, this has been posted on HN before. I seam to remember the old article having more animated illustrations. I don't know if it's the same page, same author or just similar content.
- Kliment 16y ago
  The animations are linked at the bottom of the article.

DanielStraight 16y ago

The solution to traffic jams is to not leave transportation in the hands of clueless, distracted, reckless drivers. The solution is fast, reliable, ubiquitous public transit.

stefs 16y ago
or jetpacks!
- nphase 16y ago
  or teleportation devices
nradov 16y ago
Public transit is impractical and uneconomic in many areas. The real solution is smart roads and computer-driven electric cars.
- rbranson 16y ago
  Perhaps, but in the context of the article, traffic jams only exist because of commuters. The interstate & highway systems were not designed for commuters and should not be used for them. While I think computer-driven cars will be a boon to the environment and economy, the capital investment needed is pretty fantastic, which is going to be some decades off. In fact, a real solution to this problem that could be applied in the design of our current urban landscape would be a multi-pronged effort to spread out the commuter traffic. Alternating work and school hours could widen commuting hours and distribute load across all commuter infrastructure. Increased levels of telecommuting would also contribute to this. This would be a sort of supply-side fix to commuter congestion. Local or regional governments could create incentives to encourage these changes.
  - nradov 16y ago
    The first-generation interstate highway system wasn't designed for commuters, but everything added or upgraded in the past 40 years has been. Many new luxury cars already come with limited computer driving, in the form of adaptive cruise control. The capital investment is small and rapidly dropping, and just that one innovation could deliver a major reduction in traffic congestion. http://www.springerlink.com/content/p56714553g82r2h7/ http://www.springerlink.com/content/p56714553g82r2h7/

fbnt 16y ago

Maybe the author never heard anything about green waves. http://en.wikipedia.org/wiki/Green_wave http://en.wikipedia.org/wiki/Green_wave

superk 16y ago
Green waves are a pet peeve of mine. They've tried to implement these where I lieve... a spectacular failure. Green waves only work when there is NO traffic. Speed is regulated and the flow moves fine. During rush hour they are a disaster. Every light is backed up to previous. My light turns green, then I have to wait 10 seconds for the next light to turn green and the entire line of traffic to move, before I can advance. This usually results in a stop at each light. A much better solution is what I remember from NYC: all the lights turn green at once, all the traffic moves.

ritonlajoie 16y ago

In northern America, I think most of the cars have automatic transmission. In France, (where I live), we mostly (maybe 99% ?) have manual transmissions. Have you ever experimented a traffic jam with a manual trans. car ? You have to switch gears every 10 seconds and it's very very very annoying. I'm telling you that, because as a frequent driver (well, today I drive a bike but still) in Paris, and kind of very observant, I clearly see that most people are not doing what these drivers do in this experiment. Most of the time, everybody will let a huge space between the car behind them in order to avoid changing the gears too frequently. On the contrary, on automatic cars (I had one and drove another for 6 months in Canada), that's easier to go & stop & go & stop & go & stop, etc... Not sure if it's related, but I think it is, in a small proportion. edit: my english

maw 16y ago
Pretty sure transmission type has nothing to do with it -- traffic is stop and go in plenty of places where most cars have manual transmissions. I'm increasingly convinced that it's due to so many drivers optimizing for local minima, at the expense of not just everyone around them, but of themselves thirty seconds later.
- maw 16y ago
  Duh, I meant local maxima, of course -- at least, that's what those drivers are trying for. What they get most of the time are more like minima, of course.
vaksel 16y ago
why exactly do you need to switch gears? Just leave it in first. And engage the clutch when you are stopped.
- daten 16y ago
  If you're stuck in traffic for a long time, your leg engaging the clutch can get very tired. So you're constantly switching to neutral to rest your leg. It's also not uncommon for traffic to go from stopped, to fast enough to warrant 2nd gear, back to stopped.

daychilde 16y ago

I had the good fortune to do a three month internship in Seattle last spring. And I have to say - after growing up in Dallas, now living in Florida, and seeing traffic in other places... Seattle drivers are unique. I've seen this [appear to] work in Seattle. While I was there, I tried it, and it appeared to work. However, while I lived in Dallas, I was aware of this idea, and tried it there - and no way. People cut in, people tailgated - it completely doesn't work. So I think it partially depends on the nature of the city's drivers. And there is something special about Seattle.

daten 16y ago
I live and work in DC. I go to Dallas at least once a year and drive every day during the week and weekend. I agree this would be impossible in Dallas traffic. It doesn't feel as intentionally aggressive as DC traffic, instead it's like everyone in Dallas can't take their foot off the accelerator even if they wanted to. It's hard enough finding a space between two cars to merge, you usually have to just go for it and hope the rear car can find his brakes.
- daychilde 16y ago
  It definitely took me a while after moving away from Dallas to change some of my driving habits. I still definitely change lanes more than most drivers around here - although I do my best not to cut anyone off, and I actually let drivers in here... something definitely not done often in Dallas. It also helps that I went from a 90 minute commute (each way) to usually a 10-15 minute commute here (depending on where I've worked). Smaller towns do have some benefits...

stuaxo 16y ago

Thats what those changable speed limit signs on the motorway are trying to achieve. (I've also seen markings to keep cars 10 metres apart on some roads).

Luc 16y ago

Where I live there's something called 'block driving' (I haven't found a better translation for the Dutch word 'blokrijden'). On busy summer days, when the highway to the coast is jammed, a police car will block the highway, then drive at a constant speed (and slower than the maximum speed), with no one being allowed to pass the police car. Apparently this helps to resolve the traffic waves.

superk 16y ago
That's actually one of the solutions suggested by the author. A rolling blockcade of police cars in each lane to regulate the flow.
0x5a177 16y ago
The California Highway Patrol appears to do this in Southern California as well. I've seen a patrol car start weaving between two lanes, then three, weaving more and more until it's blocking all lanes of traffic like a weavy pace car.
- mds 16y ago
  They do that to slow or stop traffic when there's debris or an accident ahead.
- bmm6o 16y ago
  It's called "running a break", and I've only seen it used to clear debris or disabled cars out of lanes, or so that a construction crew can close a lane. It'll freak you out the first time a cop car swerves in front of you across 5 lanes of traffic.
  - davidu 16y ago
    I've definitely seen it used in both Nor Cal and So Cal to slow traffic down. They do it on I-5 fairly often during rush hour, of all times.

CaptainDecisive 16y ago

Interesting observation is that what TFA calls the "cheaters", ie those who drive to the end of their lane before merging at the last minute, may actually be doing the right thing. See Tom Vanderbilt talk about it here http://www.vimeo.com/6779064 http://www.vimeo.com/6779064. If you're interested in this there's a nice longer interview with Tom at Streetfilms http://www.streetfilms.org/tom-vanderbilt-talks-traffic http://www.streetfilms.org/tom-vanderbilt-talks-traffic or an hour long Google talk.

ajb 16y ago
He doesn't say why in the short one (I haven't watched the long one). Late mergers are definitely bad in some situations - for example, when they are merging into a slow-moving turnoff lane, blocking a whole lane of ongoing traffic.
- CaptainDecisive 16y ago
  He goes into the research a bit more in the Google talk and you see where he pulls the magic "15% improvement" from. Also he has a book (which I haven't read) called Traffic so he might explain it more or cite studies there. I agree though that it doesn't really work in all situations. Tom uses the example of two lanes merging into one for roadworks. Maybe some situations where it doesn't work are an example of poor road design by traffic engineers?

mootothemax 16y ago

Heh, I didn't realise that it had such an effect, but this is the exact same game I play when caught up in a heavy traffic: the how-long-can-I-go-before-breaking game! ;-) It could be related to driving a manual and being lazy, but it helps your concentration no end :)

Deestan 16y ago
No idea why you were at -1; your comment was informative and on topic. On a side note, I also tend to play that "game" when stuck in slow home-from-holiday traffic over the mountains. Changing speeds all the time while driving manual is such a pain.

tomjen3 16y ago

The problem with slowing down miles in front of a traffic jam is that those who normally gets of before that space now has to suffer too. In addition, most people would cut you of if you drove slower than the maximum speed.

kostko 16y ago

I remember reading this article while back: "Traffic jam mystery solved by mathematicians". http://www.physorg.com/news117283969.html http://www.physorg.com/news117283969.html So now when I'm in a jam, I just slow down instead of engaging the speedup, break pattern. Haven't looked behind me though to see if I had any effect on the traffic behind me.

DanielN 16y ago

I've tried this in Boston. Mass-holes will not stand for you to screw with their traffic jams.

cakeface 16y ago
I agree that this doesn't work well around Boston. My opinion is that the fluidity of traffic, ie. lane changing, doesn't break down at low speeds in Boston. If you let a cars length open in front of you it will fill up with a car. I tend to think that this makes efficient use of the pavement available and tends for a traffic flow that is as maximal as possible but I don't have any evidence about that.
- asmithmd1 16y ago
  If efficient use of pavement means park the most cars on it Then by all means fill every available space. Safe following distance increases with the square of the speed so higher average vehicle speeds means the road carries less traffic. The road moves the most cars around 30mph, so if traffic slows below 30 it will crash to 0mph
  - cakeface 16y ago
    Cool! What is the science backing this? Is it coming out of studies or some theoretical modeling? I've been wondering what the most efficient speed for moving traffic was on a typical highway for a while.
    - asmithmd1 16y ago
      When I don't know anything about a topic I have found Wikipedia is a good place to start http://en.wikipedia.org/wiki/Traffic_flow http://en.wikipedia.org/wiki/Traffic_flow
    - deleted 16y ago
      [deleted]
    - wbeaty 16y ago

bryanh 16y ago

So, what would happen on major interstates if highway patrols kept a steady pace? Is that a viable solution? Wouldn't they eventually run up on another wave of cars and ruin everything? I would be really interesting to see if this actually improved interstate bandwidth during rush hours. But even more interesting, I bet a good portion of drivers would get upset at the fact that there are huge, unused gaps. I wouldn't be surprised to hear from people who think it is grossly more inefficient than regular old traffic jams...

parallax7d 16y ago

I used to do this every once in a while. One thing to be aware of, are large trucks behind you at the top of hills. They tend to want to increase speed going down hills to use their velocity to climb the next. It's probably a good idea to accommodate this.

RyanMcGreal 16y ago

Yes, absolutely. This is my experience as well. Related: http://news.ycombinator.com/item?id=785498 http://news.ycombinator.com/item?id=785498

nwomack 16y ago

I've actually spent quite a bit of time pondering this. Here are my completely unscientific conclusions. Imagine a [moving] wall, on an interstate, moving at 30MPH. No matter what is happening behind this wall, it is impossible to maintain an average speed faster than the wall. You can try any amount of tricks to smooth out traffic, but it will be impossible to ever move past this wall. As long as there is a steady stream of traffic, no car will ever do more than 30MPH until this moving wall gets out of the way. So now let's, more realistically, replace the wall with a bunch of slow drives, and ask 2 important questions: 1. How to get out of this situation? -- We want these drivers to all SPEED UP! It's really as simple as this. Until these bottleneck drivers move out of the way, you can only smooth out traffic, but never increase the speed. 2. How to avoid this problem in the first place? -- In general, there will be some bottleneck. After too many cars are going through this bottleneck at once, there will be slowdown. Ideally, these bottlenecks should be identified and no more than the maximum amount of cars at a time should enter the bottleneck to decrease the speed of traffic. Of course, that's easier said than done, but I think the important thing to take away from my ramblings is this: The best way to get rid of a traffic jam is: if you are in the front of the pack and have a chance to accelerate, you should do so as quickly as possible. If everybody were to do this, average speed could then be increased.

wbeaty 16y ago
But note that there aren't any slowpokes here, instead, every single car is blocked by the car ahead of them. The people behind you think that you are the slowpoke driver. But nothing is blocking the traffic, instead the average speed of the long column of cars is determined by the spacing between cars, and that spacing is determined by psychology. In light traffic, some people go far faster than average, but nobody tries to stop them. When we arrive at heavy congestion, don't we suddenly decide to close up ranks to prevent aggressive drivers from passing, stop them from "cutting us off?" If everyone habitually blocks the speeders, then it means we've compressed the traffic pattern past the peak of maximum flow, and pushed it into the unstable realm of stop/go oscillations and standing waves or "ghost jams." Want jams to vanish? Then do as the pro truckers do and just freaking back off. Happily encourage other cars to merge ahead. (They're not "cutting you off," there's no such thing as "cutting you off." They're just trying to merge into the adjacent lane!) If traffic momentarily slows way down, everyone just make sure to keep an open space that allows merging, and you'll find that it speeds right back up again.

tobtoh 16y ago

In Melbourne, Australia, a similar concept was used to ease congestion entering freeways. We had a peak-hour problem where cars would flood the entry ramps, but struggle to merge with the existing freeway traffic - this caused people to brake/slow down which resulted in major jams. To alleviate this issue "there are traffic lights at some freeway entrances to control the flow of vehicles onto the freeway when the traffic is heavy. When operating, the lights will change quickly, so that when the light is green only one vehicle in each lane will be able to enter the freeway." (taken from VicRoads website) The lights basically cycle from red to green every 2 seconds. That's enough to regulate the flow onto the freeway and minmises jams on the entry ramp and at the merge point between the freeway and entry ramp.

tobtoh 16y ago
In fact, here is a YouTube video of the lights in operation: http://www.youtube.com/watch?v=YFrEd8qSVCc http://www.youtube.com/watch?v=YFrEd8qSVCc
colonelxc 16y ago
This is used extensively in the SF bay area.

alexyim 16y ago

A side effect of doing this is that it is much more fuel efficient to not have to go into a cycle of breaking and accelerating again.

drv 16y ago

Somewhat different from the commuter-oriented topic of the article, I've seen attempts by truckers to enforce a similar pattern in construction zones (traffic reduced by one or more lanes) on long stretches of highway: In a situation where one lane has to merge because it is closed in the distance, the "nice" drivers all merge far ahead of time, while the aggressive drivers attempt to go all the way to the end of the lane and then merge ahead of everyone, causing the kind of grinding gears described in the article. To combat this, a couple of big rigs driven in parallel in the open lane and the lane that is closed ahead block all traffic from passing. This prevents the aggressive drivers from attempting to merge at the last second, smoothing out the wave. I've seen this happen several times on cross-country trips; I wonder if the truckers coordinate over radio or just choose to do it independently. On a related note, I wonder if "lane closed ahead" signs placed too far ahead actually make this problem worse, since many drivers will immediately merge out of the closing lane far ahead of time, causing a wall of traffic if the front of the line has to slow down for aggressive last-second merges.

tectonic 16y ago

As a side note, I remember reading articles on this author's webpage almost 15 years ago. Some awesome stuff from a long-time netzen! http://amasci.com http://amasci.com