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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?

#91

Post by Leszek »

kokey wrote: post #24
cones688 wrote: post #23

Earlier quoted context omitted.

I think has a lot to do with manual transmission which allows for natural and controlled engine breaking, thus not creating the brake light to come on (and therefore the wave of copy-cat type braking).

The worst I've seen has been in Johannesburg in South Africa, where automatic transmission is rare. I used to refer to it as concertina traffic before I knew it was called a traffic wave, and the concertina is a popular instrument in South Africa amongst the ancestors of the people who are usually responsible for these waves.

> and the concertina is a popular instrument in South Africa amongst the ancestors of the people who are usually responsible for these waves

I'm not sure what you're trying to imply there, but it seems a bit racist? Or am I just being ignorant?

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

#92

Post by Roboprog »

mixmastamyk wrote: post #86
Roboprog wrote: post #58

Earlier quoted context omitted.

Now I have to slam on the breaks, instead of having a gap to avoid hard accelerate/break cycles. I'd like to avoid the wear on my car and my nerves, but it's not possible because some (expletive) person will fill the gap.

To avoid breaking, allow more space in front, including space for someone to merge in.

lather, rinse, repeat.

(or was I being trolled? see "comedy in Boston" in one of the "cousin" comments nearby)

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

#93

Post by dragonwriter »

pzxc wrote: post #67
dragonwriter wrote: post #66

Earlier quoted context omitted.

> 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.

> Okay, but the vast majority of roads do not have 4+ lanes in one direction

On a road with 1 lane per direction, trucks being restricted to the right lane except for passing has no negative impact on your preferred practice regarding use of the left lane in multilane roads.

On a road with 2 lanes per direction, trucks being restricted to the right lane except for passing exactly matches your preferred practice, though the lower truck speed limit (independent of any lane restrictions) might arguably encourage other drivers to stick in the far left lane (though, except in areas with high density of trucks, doesn't really provide any strong incentive not to follow the use the right lane for traffic, except for passing, it just increases the likelihood that non-truck traffic will want to pass trucks, which is pretty high in any case.)

The lane discipline which doesn't apply on roads with 4+ lanes in one direction thus is really even potentially even a factor in what you are concerned with on roads with exactly 3 lanes per direction.

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

#94

Post by mixmastamyk »

Roboprog wrote: post #92
mixmastamyk wrote: post #86

Earlier quoted context omitted.

To avoid breaking, allow more space in front, including space for someone to merge in.

lather, rinse, repeat. (or was I being trolled? see "comedy in Boston" in one of the "cousin" comments nearby)

The linked article in this major thread explains why this doesn't make much difference:

    http://trafficwaves.org/trafexp.html
In my experience cars are just as likely to cut in as out, and that's what the extra space is for anyway.

If you arrive any later it will be minute or two per hour, so worrying about people "getting ahead" of you accomplishes nothing. If you want to win the race against the others on the freeway tomorrow, leave 5 minutes earlier!

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

#95

Post by wbeaty »

mixmastamyk wrote: post #87
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?

The smoothing doesn't increase the road capacity, though there is likely a small benefit to mitigating the negative effects of merging. The big benefit, which the grandparent concedes, is the reduction of unnecessary fuel usage, wear and tear on the vehicle and driver. So, I consider it a win regardless.

The papers I've seen on this conclude that rear-end accidents are the major issue. Smoothing the waves can eliminate immense rush-hour delays, if this eliminates panic-braking that can cause minor daily accidents. Or as they say, "speed differentials are dangerous." In I-70 Colorado they claim that police pace-cars used to smooth out the fluctuations have cut the accident rate in half.

In theory the waves can represent a bottleneck, since the close-packed regions are low-flow, but the wide empty regions are also low-flow. If the smoothed wave results in traffic flowing at 35-40MPH, then smoothing will increase the flow, since the peak flow rate takes place at 35-40 MPH. But the increase isn't enormous. I think they said ~15%. That's nothing, when compared to the effects of removing an accident scene from a rush-hour commute.

You can play with those online JAVA simulators: set up unstable conditions on the ring-road, watch the initial flow, then after traffic-waves develop, watch the flow again. If enormous waves appear, the flow drops by ~25%, but if a string of small waves appear, the decrease is less than 10%.

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

#96

Post by wbeaty »

nradov wrote: post #73

Widespread use of adaptive cruise control basically solves this problem. That's the technology where you can set the car to follow a certain distance behind the car in front, and then it accelerates or brakes as necessary. The systems use radar or stereoscopic cameras to measure distance. Once 20%+ of cars on a road segment are using ACC then everything smooths out. Now that the price of ACC has come way down I think…

ACC just imposes safe driving behavior: proper spacing for the reaction time.

So if just 20% of humans were safe drivers (spaced out properly,) then everything smooths out.

That, or perhaps 0.5% of drivers could intentionally go at the average speed.

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

#97

Post by wbeaty »

ninkendo wrote: post #40
mixmastamyk wrote: post #2

This reminds me of a piece on traffic I read quite a few years ago and might have been on reddit or even perhaps slashdot. I still follow its advice to this day when having to brave the 101. It discussed traffic waves and our reactions to them. The repeatable waves this article mentions come from (most of) the individual drivers driving faster than the capacity of the road to carry them all. So they bunch up at some…

How can you be sure the cars behind you aren't even more compressed than they otherwise would be if you're leaving so much space in front of you like that? One thing I hated about that article was that the author assumed he was doing such a great service for everyone by "smoothing out" the traffic waves by leaving a buffer, but he never really proved it; he just waved his hands and said that it looked like the cars b…

> How can you be sure the cars behind you aren't even more compressed

Because, uh, you don't drive slow.

You drive at the average speed of traffic. Not slow. To smooth out the traffic waves, you don't come to a halt, and neither do you rush forward. "Average speed:" that's when it's not fast, and also it's not slow.

---

Myth: if you have an empty gap, you must be a slow driver!!

Debunked: yes, genuinely slow drivers have big gaps ahead, but those gaps are continuously growing. If a clot of cars is going just 1/2MPH slower than average, then the gap increases rapidly: growing a half mile for each driving hour. If that clot of cars was 5MPH slow, then in just ten minutes the gap would increase by over four thousand ft.

But on the other hand, a constant-sized gap does not decrease your speed. Whether you're 6" from the car ahead, or 6ft, or 600ft, your gap has a constant size, and you're moving at the same speed as traffic ahead.

Slow drivers do make empty gaps, but empty gaps aren't any proof of slow driving.

Heh, so maniacal aggressive tailgating doesn't actually get you to your destination any faster? AMAZING! Who'd have thought!

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