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How traffic actually works

jliszka.github.io

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Re: How traffic actually works

#101

Post by cwoods »

rdmcfee wrote: post #92
cwoods wrote: post #82

Earlier quoted context omitted.

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 j…

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 sta…

>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.

Re: How traffic actually works

#102

Post by danielweber »

jessaustin wrote: post #63
hammock wrote: post #2

That was the clearest explanation of traffic I've come across. I'm inclined to buy into it (often it seems no one knows what they're talking about when it comes to traffic). It also runs counter to what is commonly said about traffic jams. Most people focus on restoring smooth flow by doing things such as driving really slow to create space in front of you. This guy makes the case that "flow" is not really the import…

For the record, I am "that guy" who runs all the way down to the end of the closed lane before merging over. Except I don't consider it an asshole move because as OP points out, I'm making the best use of the road ahead (while allowing fewer people to merge ahead of me) In interstate travel I have noticed the increasing frequency of the "two trucks" maneuver, in which a big rig driven by someone philosophically oppos…

I wonder if good zipper merges would be more likely to happen if, instead of having lane 1 merge into lane 2, both lanes got merged into lane 1.5.

Re: How traffic actually works

#103

Post by tonyarkles »

GigabyteCoin wrote: post #80

The article claims that the maximum theoretical throughput for traffic per lane is 2,400 vehicles per hour. What if every vehicle is separated by 2 seconds of stopping time, but all vehicles are moving at the exact same speed of 200 Miles per hour? It would take one vehicle 0.005 hours to cover a mile (5,280 feet). Assuming each car had a length of 10 feet, it would take 0.005/528 = 0.0000095 hours for a vehicle to c…

I love it! It's a counterintuitive result, but if you think about it, it makes sense.

Re: How traffic actually works

#104

Post by analyst74 »

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…

Having smoother traffic is good on many grounds: happier drivers, better fuel efficiency, and what not.

But it does not make people go home faster. Let's put a simple deductive thinking practice:

If you are the first car in the jam, you are stopped and slowed by traffic lights, police, accidents or whatever, but the traffic jam does not affect you, you are going as fast as you can.

For the second car, you will not get to your destination faster than the car you're following. So however you drive, you will not be faster than following with minimal distance.

The same applies to the third car, and on ward.

Basically, the fastest way to get through a traffic jam is to follow closely, and that means stop and go.

Re: How traffic actually works

#105

Post by Lagged2Death »

Don’t let people merge in front of you, ever.

When you merge, you're merging in front of somebody, so a rule like this, universally followed, is effectively a ban on merging. How's that going to work, exactly?

Travel time isn't the only consideration. Things like safety, fuel consumption, and stress levels are important too.

Re: How traffic actually works

#106

Post by pertinhower »

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…

...which also handsomely shows the real complexity of modeling systems where the human mind is involved, and the folly of over-simplified "1 car per 2 seconds" systems that look good in a computer model but fail to capture the real experience or decisions of piloting a car.

Re: How traffic actually works

#107

Post by CWuestefeld »

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.

Re: How traffic actually works

#108

Post by susi22 »

analyst74 wrote: post #104
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…

Having smoother traffic is good on many grounds: happier drivers, better fuel efficiency, and what not. But it does not make people go home faster. Let's put a simple deductive thinking practice: If you are the first car in the jam, you are stopped and slowed by traffic lights, police, accidents or whatever, but the traffic jam does not affect you, you are going as fast as you can. For the second car, you will not ge…

Thank you for that comment. You're 100% correct. However, it again shows that it's important to distinguish between theory and practice:

IF your model is correct, the traffic jam will clear since everybody will at some point reach their desired speed of approx ~80mph again. However, the reality is differnt. The model doesn't work since people break. That's the thing that makes your "deductive thinking practice" break down: People break. To prevent this....

Wait, let me just link this:

http://www.smartmotorist.com/traffic-and-safety-guideline/tr...

Re: How traffic actually works

#109

Post by danielweber »

jessaustin wrote: post #67
dvanduzer wrote: post #44

Earlier quoted context omitted.

There is a protocol. Even in heavy traffic, if you observe the following distance that the DMV tells everyone to observe when taking a driving test there is always room to merge.

...following distance that the DMV tells everyone to observe... Who on earth leaves such a distance in stop-and-go traffic? I certainly haven't seen it. You might as well just assume that every driver will be safe, considerate, and wise.

If traffic is stop-and-go, a zipper merge is trivial.

Re: How traffic actually works

#110

Post by steamer25 »

josefresco wrote: post #14
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.

Doesn't this simply displace some of the wait to the onramp?

I used to be skeptical of ramp metering until the day I drove several miles below the speed limit to 'celebrate' the anniversary of a ticket I'd received. Instead of driving 14 MPH over the limit, I drove 14 MPH under the limit (legally that time) as a form of radical civil obedience* . As expected, this caused quite a bit of unnecessary congestion.

It actually turned out to be harder to sustain a backup* * once I entered the metered areas. The reason? Metering limits the number of idiots on the road at a given time. I.e., my attempt at being intentionally stupid was mitigated because the meters prevented the road from nearing saturation. The little bit of wiggle room on the road made it relatively straight-forward to just route around me.

So yes, in one sense meters merely move the wait from one point to another but they also remove some of the interactive effects of human stupidity.

* https://www.youtube.com/watch?v=OoETMCosULQ "I know no method to secure the repeal of bad or obnoxious laws so effectual as their strict construction." -- President Ulysses S. Grant's First Inaugural Address

* * No I did not intentionally prevent people from passing me. My beef is with the revenue centers that are the pre-emptive enforcement of low velocities--not with my fellow passer-motorists.

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