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Experiment Shows Traffic 'Shock Waves' Cause Jams
Galactic_grub writes "Japanese researchers recently performed the first experimental demonstration of a phenomenon that causes a busy freeway to inexplicably grind to a halt. A team from Nagoya University in Japan had volunteers drive cars around a small circular track and monitored the way 'shockwaves' — caused when one driver brakes — are sent back to other cars, caused jams to occur. Drivers were asked to travel at 30 kmph but small fluctuations soon appeared, eventually causing several vehicles to stop completely. Understanding the phenomenon could help devise ways to avoid the problem. As one researcher comments: 'If they had set up an experiment with robots driving in a perfect circle, flow breakdown would not have occurred.'"
1. It's brakes. Brakes. Breaks is when something stops working. 2. This is obvious to anyone who has driven much. Try not to use your *brakes* on the motorway. Try to "iron out" the waves by ever so slowly dropping back when you see them approaching.
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It's already been done here, on Slashdot - already solved by the math guys, outlined on physorg.
But really any time I can see math at work in my day-to-day commute, is a good day to me. Also, it's fun to reach out and "touch" the asshole 200 yards behind you...
... as much as the next guy, but it's been done here many times. Slow news day I guess, but nobody is surprised by this. It's pretty much common sense.
See when you put cars in the article, that immediately takes away the ability to use a car analogy. No car analogies = no lively discussion, or something like that. It's an approximation. Adding Natalie Portman or something involving Ron Paul changes the equation slightly, but car analogies are where it's at.
I got a catholic block.
I can't find the reference, but clearly remember reading about the physics of traffic jams 20 years ago.
I do as well, and I recall there was even software (e.g. GPSS) to simulate the phenomenon. But nice to see how an experiment validates historic findings (which have probably not made it to Google yet and thus practically do not exist).
CC.
TaijiQuan (Huang, 5 loosenings)
1998 called and wants Its amazing news back Except he even built animated Gifs to illustrate!
meh
This phenomenon is obvious also to those who have gone through basic training. Often in marches you have the accordian effect where the front group is fine but due to small time differences in stopping and starting, that are amplified backwards, the rear unit often is running and stopping. The same occurs on the road whereby one person brakes and then many others brake before they need to. When traffic moves, people tend to start slower than needed. This is what creates these "phantom menaces" that backup traffic for no reason. Oh, that and people don't know how to merge correctly!
Wow, I thought this was common knowledge already, at least within traffic engineer circles. In my little world, anyway here's a report from 1994...
Graduate students and most professors are no smarter than undergrads.
They're just older.
"City hall" in German is "Rathaus" Kinda explains a few things......
Ditto with "estimating" velocity correction or even just velocity and the velocity of the guy ahead - you don't have to explicitly introduce errors, they're already part of the system (we wouldn't call it an estimate otherwise). Heck, even making sure that you're actually travelling at the velocity you think you're travelling at is not all that easy - there are a lot of mechanical parts between you and the wheels on the road, they'll introduce fluctuations (including the wheels and the road themselves) - so just because you figured that injecting 5mg more petrol for the next 62.54235ms will make you reach your optimal speed of exactly 30km/h, that don't make it so; there will always be a small error.
Point being, there is no such thing as perfection in the real world and I would advise you never to expect that of a robot or other device. Errors may be small and therefore neglectable, but they exist.
Physical experiments have their limits too. What's practical about drivers running around in circles? Real roads have fluctuating traffic loads, blind turns, merging and diverging traffic and a host of other obstacles. The point of an experiment is controlled conditions to gain fundamental constants and other descriptors. What you might get from this experiment is better statistics on driver reaction time and a few other constants to refine you models.
When you really want to know how a road is going to perform, you take it to some kind of Monte Carlo simulation.
Friends don't help friends install M$ junk.
I've seen this in a textbook published in 1998, which contains references to papers dating from the 1960's. That text highly recommendeds a collection of review articles found here, and what appears to be a later book by the same author is here.
Camping on quad since 1996.
It's not. This guy was an amateur looking at the problem a decade ago. Geez, not THAT guy again. His observations on what causes that stuff are spot on, but his proposed solutions show a complete inability to understand the concept of scaling as it applies to traffic. He notes that by keeping a larger interval in front of him, the "wave" disappears. Well no shit. Doing that simulates a small pocket of uncongested freeway. This pocket is created at the (small) expense of the cars behind him. You can't have everyone leave a larger interval because that would require the road to be carrying fewer cars. The waves are caused by too many cars too close together. no amount of driving "tricks" is going to increase the car-to-car interval without actually reducing traffic density.
Commendable effort, but it's further proof of what my father (an engineer) has always said about engineers "Never ask an engineer to solve a problem outside his area of expertise. You'll get the most plausible sounding wrong answer you've ever heard." To respond to your specific claim:
The goal is not traffic density (cars per mile of roadway, f'ex) but rather traffic throughput (cars per hour).
If you double following distance you reduce density by half*. If you were to continue at the same speed you'd also cut throughput by half. But if the extra following distance avoids propagating perturbations that would cause slowdowns your average speed may well more than double thereby increasing throughput.
And it may not, but your claim is insufficient to show increased following distance is counterproductive to throughput (never mind safety concerns).
* Since horses are all frictionless spheres, naturally cars must have zero length.
P.S. The linked site is truly one of the classics of the internet. I believe it's been posted on slashdot before. And then presumably duped a couple times for good measure.