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What an arrogant article. How can you title something 'How traffic actually works' when you don't examine actual traffic. Instead, make up a simple model, run s

What an arrogant article. How can you title something 'How traffic actually works' when you don't examine actual traffic. Instead, make up a simple model, run some code, claim it shows what you want. It's not like modelling traffic is so insanely hard that we need such simplistic models. Pick as complex a model as you like; we have the computing power to simulate it!

leothekim 13y ago
If you RTFA, he compares the results of the model to actual data collected by the Federal Highway Administration. Why use a complex model when a simple one suffices?
- msane 13y ago
  Not a fan of the use of "RTFA".
analyst74 13y ago
What author is trying to argue against is the idea of "smoothing-the-wave", which he does prove in his overly complicated article. Yes, there is too much rambling for making a point, yes the tone of title is quite arrogant / link-baity. But this terrible essay did prove the point: smoothing the wave is not going to make you go faster.
- dvanduzer 13y ago
  He utterly fails to make that point. His simple model explains the idea of maximum throughput / congestion. It utterly fails to explain the extreme variance in real traffic throughput during congestion. The original article does.
  - jliszka 13y ago
    OP here. That's a really good point. I just think the original article overreached in saying that zipper merging is a "simple cure" for traffic jams, without taking into account that the road might at or near capacity (and you hit capacity in a hurry when you lose a lane). My article doesn't account for variance in flow rates in congested traffic, but variance in car length (% of trucks on the road) might explain it. I'm not convinced that merging behavior is the culprit; the original article only speculates that that's the case. I'm putting forward a reasonable explanation for why that isn't the explanation, and a basis for evaluating whether it might be — in particular, whether a zipper merge results in higher flow rates after the bottleneck.
    - jliszka 13y ago
      FWIW I tried this out, seeing what happens when there are varying average car lengths on the road. http://jliszka.github.io/assets/img/traffic/speed-vs-occupancy-2.png http://jliszka.github.io/assets/img/traffic/speed-vs-occupan... http://localhost:4000/assets/img/traffic/flow-vs-occupancy-2.png http://localhost:4000/assets/img/traffic/flow-vs-occupancy-2... Also added as an update to the article.
    - rhizome 13y ago
      Isn't variance in flow rate the crux of the issue? Merge lanes are a special case in traffic, where another flow is entering the channel. This creates turbulence around the merge point that does not exist where there is pure laminar flow and all lanes can be treated equally. Would it help if "simple cure" was renamed as a "simple improvement?"
      - Arelius 13y ago
        This. Sure, there exists a point where the input flow is great enough that traffic must move slower. OP's entire argument is based off of this. The problem is that there are many things you can do to slow down the flow rate even further, and merging poorly creates this "turbulence" which wastes further flow. And, it's clear that no improvement in merging behavior can beat the maximum road occupancy, however we can approach that limit much more closely. I think that conceptually modelling traffic as fluid flows is quite clever, and the "turbulence" idea is particularly satisfying.
- admax88q 13y ago
  It also won't make you go slower. And rolling at a constant low speed is much less frustrating than constant stop and go traffic. Especially for people driving standard. It's also more fuel efficient.
  - kcorbitt 13y ago
    I've always tried to smooth the wave on the fuel efficiency argument. I figure that maintaining a constant low speed has got to use less gas and be easier on my car than all the stopping and starting.
    - deleted 13y ago
      [deleted]
- jerf 13y ago
  I'm not sure who actually thought that "smoothing the wave" did make you actually go faster though, since a moment's thought shows that "going faster" would necessarily involve going through the bumper of the car in front of you. I think it's about a "laminar" traffic flow being a lot less annoying and dangerous to drive in, if you are going to go slow. I think he fell down on his own argument when he claims that doing that causes a "big traffic jam" downstream of you; how can it, if you're only 10 or 20 seconds max further behind than you otherwise would be? You can only cause that much additional "traffic jam" in the back, and it may well be worth it to create a more laminar flow.
  - SilasX 13y ago
    >I'm not sure who actually thought that "smoothing the wave" did make you actually go faster though, Probably all the people that passed around the critiqued link and suggested that it gives a way to improve traffic flow?
    - j-kidd 13y ago
      The gist I get from the link is that the act of "smoothing the wave" will not benefit the one who performs the act, but it benefits the drivers behind the lane. You can't fix the traffic jam in front of you, but you can do your part to prevent one from forming behind you. And that's why people pass around the link.
      - SilasX 13y ago
        Right: like I said -- and like the GGP (jerf) just denied them saying -- the claim is that it will hasten the traffic flow. Individual vs group benefits is beside the point.
nether 13y ago
He's derived the fundamental diagram of traffic flow: https://en.wikipedia.org/wiki/Fundamental_diagram_of_traffic_flow https://en.wikipedia.org/wiki/Fundamental_diagram_of_traffic.... Up next: why F = ma really, really matters for space launches. Experts don't know this!
- hayksaakian 13y ago
  "1 weird trick for successful space flight"
  - angersock 13y ago
    Lockheed Martin hates this guy!
cwoods 13y ago
Agree 100%. From the article: >Suppose you’re on a 2-lane (each way) highway and one lane is closed up ahead due to construction. Now the flow rate of your lane is cut in half (or there are twice as many cars in line in front of you, depending on how you want to look at it). What I observe is that the speed is reduced to one twentieth of the speed, not just half. This is because people are merging very slowly while jostling resulting in needless braking. If everyone could agree upon a proper zipper merge, the speed for everyone would go up many times. Or imagine a traffic signal at the merge point that only lets one lane go through for a minute each. The overall flow rate would be much higher than what it is without such a signal. Discounting this based on theoretical flow rate (as if removing one lane reduces real traffic flow by only 50%) shows that the author totally ignores real traffic scenarios completely at odds with the title of the article.
- rdmcfee 13y ago
  I think you're may be thinking of this as one mechanism instead of two separate mechanisms. You are dealing with a queue as well as a through-rate at the merge-point. The through-rate with one lane can still be 1/2 of the through-rate with two lanes, but because you have a queue waiting to reach the merge-point you can end up waiting much longer. More spacious merging will not change this because of the principle stated in the first paragraph of the article. Increasing the speed at the merge-point will not decrease the queue. It will only decrease the density of the queue but move it back further in traffic. Your time to cross the merge-point will be basically the same.
  - cwoods 13y ago
    >Increasing the speed at the merge-point will not decrease the queue. It will only decrease the density of the queue but move it back further in traffic. Your time to cross the merge-point will be basically the same. I have to disagree with this. If you increase the speed at the merge point, someone who is newly joining the queue will definitely cross the merge point in lesser time than with lesser speed at the merge point.
    - 13y ago
rdmcfee 13y ago
The initial point about rate of vehicles through a specific point per lane per hour couldn't be more simple and valid.
danielweber 13y ago
I think lots of people, on both "sides" of this debate, have predetermined notions and are trying really hard to justify them.

leothekim 13y ago

If you RTFA, he compares the results of the model to actual data collected by the Federal Highway Administration. Why use a complex model when a simple one suffices?

msane 13y ago
Not a fan of the use of "RTFA".

analyst74 13y ago

What author is trying to argue against is the idea of "smoothing-the-wave", which he does prove in his overly complicated article. Yes, there is too much rambling for making a point, yes the tone of title is quite arrogant / link-baity. But this terrible essay did prove the point: smoothing the wave is not going to make you go faster.

dvanduzer 13y ago
He utterly fails to make that point. His simple model explains the idea of maximum throughput / congestion. It utterly fails to explain the extreme variance in real traffic throughput during congestion. The original article does.
- jliszka 13y ago
  OP here. That's a really good point. I just think the original article overreached in saying that zipper merging is a "simple cure" for traffic jams, without taking into account that the road might at or near capacity (and you hit capacity in a hurry when you lose a lane). My article doesn't account for variance in flow rates in congested traffic, but variance in car length (% of trucks on the road) might explain it. I'm not convinced that merging behavior is the culprit; the original article only speculates that that's the case. I'm putting forward a reasonable explanation for why that isn't the explanation, and a basis for evaluating whether it might be — in particular, whether a zipper merge results in higher flow rates after the bottleneck.
  - jliszka 13y ago
    FWIW I tried this out, seeing what happens when there are varying average car lengths on the road. http://jliszka.github.io/assets/img/traffic/speed-vs-occupancy-2.png http://jliszka.github.io/assets/img/traffic/speed-vs-occupan... http://localhost:4000/assets/img/traffic/flow-vs-occupancy-2.png http://localhost:4000/assets/img/traffic/flow-vs-occupancy-2... Also added as an update to the article.
  - rhizome 13y ago
    Isn't variance in flow rate the crux of the issue? Merge lanes are a special case in traffic, where another flow is entering the channel. This creates turbulence around the merge point that does not exist where there is pure laminar flow and all lanes can be treated equally. Would it help if "simple cure" was renamed as a "simple improvement?"
    - Arelius 13y ago
      This. Sure, there exists a point where the input flow is great enough that traffic must move slower. OP's entire argument is based off of this. The problem is that there are many things you can do to slow down the flow rate even further, and merging poorly creates this "turbulence" which wastes further flow. And, it's clear that no improvement in merging behavior can beat the maximum road occupancy, however we can approach that limit much more closely. I think that conceptually modelling traffic as fluid flows is quite clever, and the "turbulence" idea is particularly satisfying.
admax88q 13y ago
It also won't make you go slower. And rolling at a constant low speed is much less frustrating than constant stop and go traffic. Especially for people driving standard. It's also more fuel efficient.
- kcorbitt 13y ago
  I've always tried to smooth the wave on the fuel efficiency argument. I figure that maintaining a constant low speed has got to use less gas and be easier on my car than all the stopping and starting.
  - deleted 13y ago
    [deleted]
jerf 13y ago
I'm not sure who actually thought that "smoothing the wave" did make you actually go faster though, since a moment's thought shows that "going faster" would necessarily involve going through the bumper of the car in front of you. I think it's about a "laminar" traffic flow being a lot less annoying and dangerous to drive in, if you are going to go slow. I think he fell down on his own argument when he claims that doing that causes a "big traffic jam" downstream of you; how can it, if you're only 10 or 20 seconds max further behind than you otherwise would be? You can only cause that much additional "traffic jam" in the back, and it may well be worth it to create a more laminar flow.
- SilasX 13y ago
  >I'm not sure who actually thought that "smoothing the wave" did make you actually go faster though, Probably all the people that passed around the critiqued link and suggested that it gives a way to improve traffic flow?
  - j-kidd 13y ago
    The gist I get from the link is that the act of "smoothing the wave" will not benefit the one who performs the act, but it benefits the drivers behind the lane. You can't fix the traffic jam in front of you, but you can do your part to prevent one from forming behind you. And that's why people pass around the link.
    - SilasX 13y ago
      Right: like I said -- and like the GGP (jerf) just denied them saying -- the claim is that it will hasten the traffic flow. Individual vs group benefits is beside the point.

nether 13y ago

He's derived the fundamental diagram of traffic flow: https://en.wikipedia.org/wiki/Fundamental_diagram_of_traffic_flow https://en.wikipedia.org/wiki/Fundamental_diagram_of_traffic.... Up next: why F = ma really, really matters for space launches. Experts don't know this!

hayksaakian 13y ago
"1 weird trick for successful space flight"
- angersock 13y ago
  Lockheed Martin hates this guy!

cwoods 13y ago

Agree 100%. From the article: >Suppose you’re on a 2-lane (each way) highway and one lane is closed up ahead due to construction. Now the flow rate of your lane is cut in half (or there are twice as many cars in line in front of you, depending on how you want to look at it). What I observe is that the speed is reduced to one twentieth of the speed, not just half. This is because people are merging very slowly while jostling resulting in needless braking. If everyone could agree upon a proper zipper merge, the speed for everyone would go up many times. Or imagine a traffic signal at the merge point that only lets one lane go through for a minute each. The overall flow rate would be much higher than what it is without such a signal. Discounting this based on theoretical flow rate (as if removing one lane reduces real traffic flow by only 50%) shows that the author totally ignores real traffic scenarios completely at odds with the title of the article.

rdmcfee 13y ago
I think you're may be thinking of this as one mechanism instead of two separate mechanisms. You are dealing with a queue as well as a through-rate at the merge-point. The through-rate with one lane can still be 1/2 of the through-rate with two lanes, but because you have a queue waiting to reach the merge-point you can end up waiting much longer. More spacious merging will not change this because of the principle stated in the first paragraph of the article. Increasing the speed at the merge-point will not decrease the queue. It will only decrease the density of the queue but move it back further in traffic. Your time to cross the merge-point will be basically the same.
- cwoods 13y ago
  >Increasing the speed at the merge-point will not decrease the queue. It will only decrease the density of the queue but move it back further in traffic. Your time to cross the merge-point will be basically the same. I have to disagree with this. If you increase the speed at the merge point, someone who is newly joining the queue will definitely cross the merge point in lesser time than with lesser speed at the merge point.
  - 13y ago

rdmcfee 13y ago

The initial point about rate of vehicles through a specific point per lane per hour couldn't be more simple and valid.

danielweber 13y ago

I think lots of people, on both "sides" of this debate, have predetermined notions and are trying really hard to justify them.