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How traffic actually works

jliszka.github.io

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Re: How traffic actually works

#161

Post by losvedir »

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…

Flying through a light that just turned green for you is a good way to hit a pedestrian or someone coming in from the left or right trying to catch the tail-end of their yellow.

Please don't do this.

Re: How traffic actually works

#162

Post by dmckeon »

kens wrote: post #126
CWuestefeld wrote: post #107

Earlier quoted context omitted.

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

The California fast-vs-passing lane pattern also emerges due to two things that California requires that other US states tend not to require: semi-trucks must go slower and keep right.

From the handbook cited above, or see also signage on many CA highways: The maximum speed limit on most California highways is 65 mph. You may drive 70 mph where posted. Unless otherwise posted, the maximum speed limit is 55 mph on two-lane undivided highways and for vehicles towing trailers.

... When you tow a vehicle or trailer, or drive a bus or three or more axle truck, you must drive in the right hand lane or in a lane specially marked for slower vehicles. [emphases added]

On divided highways of 2 or 3 lanes in each direction, such as I-5 in the Central Valley, these requirements strongly separate traffic into 2 sets - semi-trucks doing 55-ish in the right lane, and non-trucks doing 65-70-ish in the "fast" lane. (okay, yes, 85-ish, except in Kern County).

The results are that 1) over-the-road truckers dislike driving in CA, and 2) CA non-truck drivers quickly learn to avoid the right lane.

The other 49 US states tend to have more of a "keep right except to pass" pattern, depending of course on other local variations, especially population density, traffic volume, and similar.

Source: someone who drives (and tows) in 18+ states per year.

Re: How traffic actually works

#164

Post by SilasX »

j-kidd wrote: post #141
SilasX wrote: post #133

Earlier quoted context omitted.

>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?

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.

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.

Re: How traffic actually works

#165

Post by jliszka »

susi22 wrote: post #146
jliszka wrote: post #122

Earlier quoted context omitted.

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.

I just read some of your older blog posts. They're close to my research and well written and very informative. Keep up the good work! Cheers

Thanks! What's your research on?

Re: How traffic actually works

#166

Post by corin_ »

losvedir wrote: post #161
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…

Flying through a light that just turned green for you is a good way to hit a pedestrian or someone coming in from the left or right trying to catch the tail-end of their yellow. Please don't do this.

Surely most (all) lights leave a significant gap between one set of people going red and the next going green. Of course, people noticing this gap may think "well it only went red two seconds ago, so I have time" - which would mean not shooting off at the green makes you safer - but if people get used to everyone else waiting 2 seconds after it turns green, then suddenly they have even more time after their turn goes red to make it through...

Re: How traffic actually works

#167

Post by [deleted] »

kcorbitt wrote: post #81
admax88q wrote: post #76

Earlier quoted context omitted.

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.

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]

Re: How traffic actually works

#168

Post by susi22 »

teddyh wrote: post #123
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.

I have to correct myself: Yes you're correct. I thought that the top left blinking arrow indicated that a car passed but that's very wrong. It's just displaying the road construction arrow and the rate or cars is indeed about twice as high.

Re: How traffic actually works

#169

Post by msandford »

mavhc wrote: post #157
cwoods wrote: post #101

Earlier quoted context omitted.

>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…

That doesn't matter though, as if they're going faster they're more spaced out. Only 2000 cars per hour can pass the merge point

Sure, but when traffic jams happen you often see not just ONE lane of traffic slowing down at the merge point but ALL lanes of traffic slowing down. On a four lane freeway narrowing to three lanes it's not the case that the two right lanes are stop & go and the two left lanes are 80MPH. EVERYONE slows to 10MPH. Furthermore the notion that you'll get 2000 cars per hour at the merge point irrespective of speed is ludicrous. Once everything slows down people act really douchey and don't let each other merge, etc.

I have witnessed eight lanes of traffic slow from 70MPH to 10MPH over a single poorly designed merge when there was more than enough aggregate free space for the merge. That happened because drivers don't accelerate hard enough on onramps and people don't redistribute themselves prior to shitty merges.

Show me a society that has no traffic jams and I'll show you one that's ready for socialism. Or vice versa.

Re: How traffic actually works

#170

Post by gqvijay »

Hmm. Interesting. I have always contemplated this problem. First, I want to simplify the problem a bit and hope it'll apply to traffic jams. I think the problem is human reaction time. I must be missing something but hardly people talk about this. (although my solution might not be feasible). Let me explain.

So, lets say you are stopped behind 30 cars and the first car is waiting for the red to turn green. Now, as soon as it turns green, it takes a second (or two) for the first car to start moving. After that second, second car adds another second before starting to move. Based on this, you won't move your car until 30 seconds have passed. Isn't this one of the big issue? If all of 50 cars instantly start driving once it hits green, wouldn't it reduce traffic jam greatly. Now, I do realize this is not feasible but if computers were controlling the car, 50th car can move instantly after green.

On a side note, I realize the bottleneck situation can't be solved easily BUT again, I think human reaction (response) time is a huge part of it in most of these scenarios. If computers were driving, I wonder if we can have 10 times the car we have today without traffic jams.

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