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What Are Traffic Waves and Why Do They Happen So Much?

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Re: What Are Traffic Waves and Why Do They Happen So Much?

#61

Post by irl_zebra »

knodi123 wrote: post #44

Does anyone else remember the scene in Mission Impossible 3, where tom cruise is hosting a dinner party full of guests who only know his fake cover identity as a statistician working on traffic waves for the department of transportation? The movie portrays it as conversational kryptonite, where he briefly discusses traffic issues in order to weaponize boredom and get some people to leave him alone. That part broke my…

I remember this, and actually thought the same thing. It led me to do some research and I came across a pretty interesting page on the topic of smoothing out waves of traffic. It's an old site and I was just able to re-find it just now, but perhaps you will find it interesting:

http://trafficwaves.org/trafexp.html

Re: What Are Traffic Waves and Why Do They Happen So Much?

#62

Post by Throwaway1224 »

blunte wrote: post #15

One point that seems often forgotten (or undervalued) is the great different in deceleration vs acceleration. Cars (especially driven by humans) decelerate much more quickly than they accelerate. I didn't get the impression from the simulation that this difference was realistically represented. I think reality is even worse than this simulation illustrates.

for those who tl:dr... this ^^^

Re: What Are Traffic Waves and Why Do They Happen So Much?

#63

Post by pzxc »

greggyb wrote: post #53
dismal2 wrote: post #51

If you're in the left lane and going slower than the guy behind you, pull to the right. I wish people in America would be taught this, I'm amazed at how often light traffic I encounter is from a few people meandering in the left most lanes and then everyone behind just matching their speed. Obviously does nothing about major traffic but still annoying. Besides that, people need to stop thinking of driving as a compet…

In my driving experience in the US: If a highway has two lanes, the average speed in the left lane is higher than the average speed in the right, but the only major passing opportunities are on the right when there's an empty stretch (because no one merges right). If a highway has >2 lanes, the left is never consistently the fastest moving lane, and almost every passing opportunity comes from moving right. It is not…

California is the worst about this and if that's where you live may be giving you a false impression of the US as a whole. It's probably because in California, 18-wheelers are required to stick to the right lane and have a lower speed limit (55 instead of 65). That's not true in most other states.

I, too, have noticed that people here tend to just pick a lane (usually the left one to avoid trucks) and stick to it no matter the speed they're going. However, my experience in the other two states I've lived in (Florida, Indiana) and the other 35+ states I've visited, is that most people in the US know that the left lane is for passing and are somewhat more considerate about this.

Drivers have trouble merging in all 50 states, though. Half the people merge as soon as possible, thinking it's more polite to merge sooner rather than later (or just not wanting to fight for an opening or get angry looks from people who believe merging early is better), and half the people merge as late as possible, attempting to do the zipper merge which is actually the most efficient means of merging and what everyone should do.

Re: What Are Traffic Waves and Why Do They Happen So Much?

#64

Post by drzaiusapelord »

dismal2 wrote: post #51

If you're in the left lane and going slower than the guy behind you, pull to the right. I wish people in America would be taught this, I'm amazed at how often light traffic I encounter is from a few people meandering in the left most lanes and then everyone behind just matching their speed. Obviously does nothing about major traffic but still annoying. Besides that, people need to stop thinking of driving as a compet…

Maybe on some tiny two lane rural highway can you get away with the left being only a passing lane, but in an urban congested 10-12 lane expressway with exits on both the left and right, well, those rules just don't apply.

The reality is that cars are becoming very ineffcient methods of transport. Most carry only one driver, take up a lot of space, etc. The days of driving on a rural highway with two lanes and having the left lane designated as just the passing lane are long behind us. We don't have the capacity for that outside of rural areas and as more areas become congested with car traffic, the less polite people will be.

Re: What Are Traffic Waves and Why Do They Happen So Much?

#65

Post by btilly »

ninkendo wrote: post #45
morley wrote: post #42

Earlier quoted context omitted.

Whenever I see an article about traffic patterns, I inevitably see this exchange: Person 1: You can fix traffic waves by smoothing! Person 2: Smoothing traffic waves makes no sense! It's frustrating. I don't know what to believe. Is there any peer-reviewed, simulation- and data-backed research that puts this issue to bed for good?

I think the sad truth is that it doesn't matter how you drive, traffic is going to suck. Given that everyone requires a safe lead time of (for example) 1-2 seconds, the more cars there are per mile of highway, the slower everyone must drive. (You can't drive 80 miles per hour bumper-to-bumper.) So if density is say, 50% (one carlength of open space per one car), you have to drive a speed such that a carlength is 1-2s…

You are thinking about traffic in terms of cars per foot. The right way to think about it is in terms of cars passing a spot per second.

A lot of traffic problems stem from the fact that you get more cars per second from quickly moving smooth traffic than from slowly moving dense traffic. Therefore if something bad happens to rapid smooth traffic, you quickly get a phase transition into horrible traffic.

Now what does the transition from horrible traffic back to good traffic look like? The first step is that you have to get back to smooth traffic, and then that has to speed up.

If nobody smooths out traffic deliberately, then you don't get this until the volume of people wanting to pass gets so light that all of the stop spots "evaporate" on their own because there is no pressure on them. Then the road speeds up. By contrast if traffic has been smoothed, the bottom speed steadily increases, and you get back to full speed much earlier.

Plus smoothing traffic will save on your own car's wear and tear.

Oh, and on merging? Go read http://ops.fhwa.dot.gov/wz/workshops/accessible/McCoy.htm. You will find that in the real world when drivers are instructed to merge late and politiely, merging happens significantly faster, with far fewer conflicts between drivers. So how you merge actually does matter. A lot.

Re: What Are Traffic Waves and Why Do They Happen So Much?

#66

Post by dragonwriter »

pzxc wrote: post #63
greggyb wrote: post #53

Earlier quoted context omitted.

In my driving experience in the US: If a highway has two lanes, the average speed in the left lane is higher than the average speed in the right, but the only major passing opportunities are on the right when there's an empty stretch (because no one merges right). If a highway has >2 lanes, the left is never consistently the fastest moving lane, and almost every passing opportunity comes from moving right. It is not…

California is the worst about this and if that's where you live may be giving you a false impression of the US as a whole. It's probably because in California, 18-wheelers are required to stick to the right lane and have a lower speed limit (55 instead of 65). That's not true in most other states. I, too, have noticed that people here tend to just pick a lane (usually the left one to avoid trucks) and stick to it no…

> It's probably because in California, 18-wheelers are required to stick to the right lane and have a lower speed limit (55 instead of 65).

Autos with trailers and trucks (vehicles subject to the 55mph limit where other vehicles have a 65 or 70mph limit) are not generally restricted to the right lane in California.

They only are restricted to the rightmost lane on roads where: (1) where there is no other designated (by sign) set of lanes for such vehicles, and (2) The road is not a divided highway with four or more lanes in the direction of travel (where the default, without a designation, is that they are restricted to the two rightmost lanes for normal traffic, plus the next lane out for passing.)

Re: What Are Traffic Waves and Why Do They Happen So Much?

#67

Post by pzxc »

dragonwriter wrote: post #66
pzxc wrote: post #63

Earlier quoted context omitted.

California is the worst about this and if that's where you live may be giving you a false impression of the US as a whole. It's probably because in California, 18-wheelers are required to stick to the right lane and have a lower speed limit (55 instead of 65). That's not true in most other states. I, too, have noticed that people here tend to just pick a lane (usually the left one to avoid trucks) and stick to it no…

> It's probably because in California, 18-wheelers are required to stick to the right lane and have a lower speed limit (55 instead of 65). Autos with trailers and trucks (vehicles subject to the 55mph limit where other vehicles have a 65 or 70mph limit) are not generally restricted to the right lane in California. They only are restricted to the rightmost lane on roads where: (1) where there is no other designated (…

Okay, but the vast majority of roads do not have 4+ lanes in one direction, and the vast majority of roads do not have a sign indicating a different lane designation.

Re: What Are Traffic Waves and Why Do They Happen So Much?

#68

Post by leoedin »

athenot wrote: post #55

Atlanta has rolled out variable speed limits on some highways (I285) which attempt to slow down the flow BEFORE people reach the congested area. I'm not sure how well most users understand how it's supposed to help them go faster by slowing down; a bit more education could be helpful so everyone plays the game. It is a bit weird seeing the speed limit jump from 45 to 65 then to 35 within the space of a mile…

These are very common in the UK around large cities, and in my experience they work really well. As long as there's sufficient threat of enforcement (speed cameras), people stick to the speed and the whole mass of cars move along at a reasonable speed. Compared to the horrible 80 mph, 5 mph, 80 mph, 5 mph thing you get when everyone absolutely guns it to the next slowdown they're brilliant.

Re: What Are Traffic Waves and Why Do They Happen So Much?

#69

Post by joshdance »

knodi123 wrote: post #44

Does anyone else remember the scene in Mission Impossible 3, where tom cruise is hosting a dinner party full of guests who only know his fake cover identity as a statistician working on traffic waves for the department of transportation? The movie portrays it as conversational kryptonite, where he briefly discusses traffic issues in order to weaponize boredom and get some people to leave him alone. That part broke my…

Any time my friends and I talk about traffic, someone mentions that scene. :)

Re: What Are Traffic Waves and Why Do They Happen So Much?

#70

Post by bequanna »

marknow wrote: post #56

I wish, for those of us that ride motorcycles in this type of traffic in the US, that all states would adopt a sensible lane-spitting allowance for motorcycles. In country after country, lane-splitting has proven to help reduce congestion, and yet, if I try it here, I'll get a ticket. Ridiculous.

Lane splitting is legal in California.

But honestly, how does this reduce congestion? My experience is that these motorcycles often dart between cars causing drivers to swerve slightly and tap their brakes.

I would argue this makes congestion worse as it causes more cautious drivers to brake (sometimes abruptly) and almost always slow down.

Finally, it is important to consider that as a vehicle, most of us are not looking for you and make small changes from left to right while in our lanes. It is not a goal of mine to accommodate motorcycle riders while driving. Splitter beware.

I'm all for sharing the road-- be we all need to subject to the same rules.

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