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How traffic actually works

jliszka.github.io

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Re: How traffic actually works

#121

Post by rhizome »

jliszka wrote: post #77
dvanduzer wrote: post #50

Earlier quoted context omitted.

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.

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.…

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?"

Re: How traffic actually works

#122

Post by jliszka »

susi22 wrote: post #118
jliszka wrote: post #112

Earlier quoted context omitted.

> You can see on the right side how his "cars per second" is _exactly the same_ than on the left side. Yes, but there are way more cars on the left side. That is the difference. Occupancy (density) determines speed when flow rate is fixed, and that graphic is actually a perfect illustration of this. You can't make the cars on the left travel at 80mph because it would not allow for a safe following distance. One thing…

I'm sorry for the harsh critique. I think new radical ideas are great and people should question everything that's out there. But this way was not thought out well enough IMO. I hope you keep it up and maybe have a follow up post where you can fix some of the flaws. Some of your ideas are correct and noble. But always remember to take into account the real world driver and his/her behavioral flaws. Few thoughts: Inte…

Really appreciate the feedback, comes with the territory :)

I added an update to the article looking at what happens when you vary the average car length (corresponding to the % of trucks on the road), fwiw.

Re: How traffic actually works

#123

Post by teddyh »

susi22 wrote: post #86

This article is so horribly incorrect and fails right at the very beginning with the wrong assumptions and a idea that isn't thought through. What the author forgot is to take by far the most important variable into account: SPEED So let's quote the author: "The important fact: there is a limit to the number of cars that can pass by a given point on the highway in a given amount of time, and that limit is one car eve…

> You can see on the right side how his "cars per second" is _exactly the same_ than on the left side.

Is it my browser, or is this completely wrong? For me, the right side moves about double the amount of cars into the upper edge of the image. And I believe that this is the point of the section — it wouldn’t make any sense otherwise.

Re: How traffic actually works

#124

Post by jliszka »

isaacaggrey wrote: post #57
jliszka wrote: post #4

Earlier quoted context omitted.

That was a joke ;) Onramp regulators are the real answer, letting only 1 car merge into traffic at a time at a rate well under 1 every 2 seconds.

> That was a joke ;) I found your article interesting in light of the popular traffic piece you mentioned, but ending it with jokey suggestions after a fairly serious analysis doesn't really make it clear if you're joking or not. But hey, maybe @themodelplumber and I are the only two who thought you were serious.

Yeah, I failed there. The whole article started out jokey but I ended up cramming a bunch more "serious" analysis in.

Re: How traffic actually works

#125

Post by cbr »

jere wrote: post #99

I'm having a very hard time accepting the claims of original article, "The Physics Behind Traffic Jams." Recently, I've tried to perform a few basic hypermiling techniques, especially "timing a light": if I'm the first car to encounter a red light, I leave extra space and can sometimes be moving through the light at 20mph or more when it turns green instead of stopped. It seems analogous to leaving space in front of…

Vehicle sensing systems mean the basic assumption of light timing no longer holds: when you get to the light can affect how long you have to wait.

Re: How traffic actually works

#126

Post by kens »

CWuestefeld wrote: post #107
jwallaceparker wrote: post #53

I wish more drivers would follow the driving etiquette that advises one to "stay right except to pass." On every highway trip I see countless cars camped out in the left lane but moving at the same rate as the rest of traffic. One should only use the left lane for passing. Otherwise, stay right. Traffic flows smoothly when people follow this system.

I blame The Eagles. By popularizing the meme of "fast lane" in preference to that of "passing lane", they've badly damaged the laminar flow of highways, and likely contributed significantly to road rage.

It is the fast lane in California. According to the California Driver Handbook, the left lane is known as the "fast" lane (p32). They suggest if there are three lanes to use the left lane to drive faster, pass, or turn left. They also say "Do not drive slowly in the left (fast) lane." (p64)

http://www.dmv.ca.gov/pubs/dl600.pdf

Re: How traffic actually works

#127

Post by peterwwillis »

DanBC wrote: post #96
peterwwillis wrote: post #94

Earlier quoted context omitted.

If you want to prevent people from jumping the gap, speed up. If you want to be safe from random edge cases (like someone in front of you slamming on the brakes), slow down.

I'd leave at least a minimum safe distance between my vehicle and the one in front. But Parent suggested that it's a good idea to leave more space in case someone jumps in. I'm not sure I understand that - if they jump in it's always dangerous because you don't know what the person behind you is going to do and you don't know when the jumper is going to jump in. Thus, you want to try to prevent them jumping. This is…

The stopping distance of my car (a Lexus IS300) at 70mph is 171 feet. So I know I need over 14 car lengths in front of me for me not to hit anyone with brakes at full power.

Do I actually leave that much space in front of me every time I drive 70mph? Hell no. But the slower the cars beside me are going, the quicker i'm going to hit one if it pulls in front of me. If they were going 70mph too, I would only have to brake down to, say, 65mph, which would should only take a second. But if they're going 10mph, I now have to come to an almost complete stop to prevent from hitting them, which as you can see above is a lot of car lengths.

Re: How traffic actually works

#128

Post by Evolved »

I've tested this theory and others on my commute. Whether I speed up and never let anyone in (nearly impossible since someone won't care and will merge knowing you'll most likely not hit them) or keep a good 7-10 car distance, it doesn't matter. My commute on the freeway with either of these two ways or on side streets is always 45 minutes +/- 1 minute.

The difference is I'm using less gas and putting less wear on my clutch, brakes, etc. by leaving a big gap between myself and the cars in front of me.

Furthermore I find that my demeanor is much more calm and relaxed when I leave a big gap because I'm not tensing up to avoid rear ending someone every time I stop.

Re: How traffic actually works

#130

Post by interurban »

colanderman wrote: post #91
jameshart wrote: post #17

Earlier quoted context omitted.

re spinning up a new lane: the A38-M Aston Expressway into Birmingham, UK dynamically multiplexes its lanes together into variable width channels depending on the required upstream/downstream bandwidth :) - http://i3.birminghammail.co.uk/incoming/article1294911.ece/A...

There are highways in the US that do this with dividers. A specialized vehicle drives over them and shifts them one lane to the left/right twice each day.

A good example would be the Golden Gate Bridge (at least they used to do this, I haven't been to the west coast in several years).
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