The Price of Anarchy
December 27, 2008 11:23 PM   Subscribe

Braess' paradox and the price of anarchy [PDF]: "We had three tunnels in the city and one needed to be shut down. Bizarrely, we found that car volumes dropped. ... We discovered it was a case of Braess' paradox, which says that by taking away space in an urban area you can actually increase the flow of traffic, and, by implication, by adding extra capacity to a road network you can reduce overall performance."

The Price of Anarchy in Transportation Networks is the paper mentioned in the first link — see that for maps of Boston, London, and Manhattan that show which roads were beneficial to block (individually) in a simulation. If you are interested in selfish networks and are not afraid of math, check out Selfish Routing and the Price of Anarchy (review) as well as this paper for some bounds on the price of anarchy.
posted by parudox (15 comments total) 40 users marked this as a favorite

 
YOU CAN'T CUT BACK ON FUNDING! YOU WILL REGRET THIS!
posted by Your Disapproving Father at 11:48 PM on December 27, 2008 [4 favorites]


So that's what it's called! I read about this in Nature many years ago but forgot the name, and it's onle of those concepts that's hard to google for without a label. Now that I can find it:

Cohen's mechanical analogue of Braess' paradox is a simple party trick (though only suitable for particularly nerdy and sober parties) which can be performed without any need for roads or even autonomous agents.
posted by Canard de Vasco at 12:18 AM on December 28, 2008 [7 favorites]


It's not the price of anarchy, it's the price of a crappy system.

For example, once upon a time they resealed the asphalt where I work. We have a three tiered parking lot where the lowest tier is the most desired and the upper tiers are referred to as "parking where the goats live".
They put down the fresh sealer on one weekend and when the repainted the "park here" lines the next. So a week of total chaos, right?

Instead, there was almost no one in the upper lot in the morning because people took only as much space as they really needed, rather than everyone using a parking spot sized to fit the new Ford Priapism SUV. Yes, it's a joke.

Where things went to hell was after lunch since the parking spaces were now defined (by other cars) and a spot that held a Cooper Mini was not going to fit a midsized model much less a truck or SUV.

I used to be an anarchist but I quit. There were too many rules.
posted by Kid Charlemagne at 12:26 AM on December 28, 2008


You know, I looked at the Cohen's mechanical analogue and thought, "That doesn't seem paradoxical, it's just resistors in parallel vs resistors in series only with rubber bands."

And then I realized why two routes doesn't equal 2/3 of three routes.
posted by Kid Charlemagne at 12:33 AM on December 28, 2008


Price of chaos and selfishness, no the price of anarchy.
posted by cthuljew at 12:53 AM on December 28, 2008


A few months ago I was taking a taxi in Melbourne's eastern suburbs, where a new freeway has just opened, and the taxi driver told me that he didn't expect it to drastically improve suburban traffic congestion, although it would cut the travel time for trips from certain As to certain Bs. The reason being that courier companies use sophisticated route-planning software that takes into account traffic levels, route length etc to plan an optimal route, and would quickly suck up any excess "bandwidth" provided by the new freeway by re-routing delivery vans or switching from depot-to-depot trucks to swarms of vans if it proved even fractionally more cost-efficient.
posted by L.P. Hatecraft at 1:04 AM on December 28, 2008


The optimum flow occurs when the available routes are reduced to a single circle.
posted by StickyCarpet at 1:17 AM on December 28, 2008


Also, Canard de Vasco, the diagram in that article is really, really confusing. Figured I'd improve it for anyone who was also confused: http://www.s1e1.com/stuff/springfig.png
posted by cthuljew at 1:29 AM on December 28, 2008


If anyone finds stuff like this interesting, I recommend the book Suburban Nation by Duany, Plater-Zyberk, and Speck.
posted by Nattie at 2:02 AM on December 28, 2008 [1 favorite]


I was a visitor to Reading PA recently and I think I may have chanced upon an area built on this theory! On Papermill Road at Meridian Blvd there is a shopping center where you literally cannot make a left turn into any business without going all the way around to the light and down a winding drive, not even the convenience store or gas station. Sure, the traffic pattern works great but it's damn inconvenient just to drive through McDonald's.
posted by tamitang at 3:33 AM on December 28, 2008


Interesting. I imagine it would be hard to close offf roads in practice because the large number of people who benefit overall from the reduction in average journey time will not express any gratitude, whereas the people whose favourite route you just cut will protest vigorously.
posted by Phanx at 3:35 AM on December 28, 2008


Is this post eponysterical?
posted by sfts2 at 3:42 AM on December 28, 2008


This reminds me of all of the Hans Monderman stuff. I love counter-intuitive traffic design.
posted by adipocere at 6:13 AM on December 28, 2008


In suburban Southern California, there is a condition that happens that has really made me wonder about exactly this sort of thing. A typical suburban intersection on arterial streets might have two to three travel lanes on each street, and a left turn lane on each street. And frequently, the power goes out. You'd think that these intersections would become nightmares - yet bizarrely, they often - maybe even always - seem to function much more smoothly when they operate as stop sign controls (flashing red, or off entirely). Reservoir stacking is reduced, wait times are reduced, and people seem to be pretty happy about it.

I have seen this happen so often I have begun to think that removing traffic controls would be a better deal all around - of course the problem happens when you throw lawyers into the mix (another Southern California plague). Traffic controls become mandatory, since that's how the "standard of care" is measured. Data be damned and efficiency is not what it's all about.

And honestly, you will get almost 100% resistance from traffic engineers and the infrastructure design and construction complex if you try to change things. So many of these guys have resigned all hope of original thought and live with a leatherbound copy of AASHTO Green Book on a little shrine in the front hallway of their house where the Bible used be...it's sickening. You could try to change AASHTO...good luck with that.

As a landscape architect who is sometimes charged with street design, I can't tell you how many times I or a colleague have tried to use rational arguments with these guys, and literally been greeted with a zombie like stare as the Engineer tries to grasp for a rebuttal to our arguments...only to fumble for the argument of last resort....
"It's not The Standard."
posted by Xoebe at 7:20 AM on December 28, 2008 [1 favorite]


There is indeed a school of thought that traffic controls lead to dangerous conditions.
posted by nev at 6:45 AM on December 30, 2008


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