Conventional traffic engineering assumes that given no increase in vehicles, more roads mean less congestion. So when planners in Seoul tore down a six-lane highway a few years ago and replaced it with a five-mile-long park, many transportation professionals were surprised to learn that the city’s traffic flow had actually improved, instead of worsening. “People were freaking out,” recalls Anna Nagurney, a researcher at the University of Massachusetts Amherst, who studies computer and transportation networks. “It was like an inverse of Braess’s paradox.”
The brainchild of mathematician Dietrich Braess of Ruhr University Bochum in Germany, the eponymous paradox unfolds as an abstraction: it states that in a network in which all the moving entities rationally seek the most efficient route, adding extra capacity can actually reduce the network’s overall efficiency. The Seoul project inverts this dynamic: closing a highway—that is, reducing network capacity—improves the system’s effectiveness.
Although Braess’s paradox was first identified in the 1960s and is rooted in 1920s economic theory, the concept never gained traction in the automobile-oriented U.S. But in the 21st century, economic and environmental problems are bringing new scrutiny to the idea that limiting spaces for cars may move more people more efficiently. A key to this counterintuitive approach to traffic design lies in manipulating the inherent self-interest of all drivers.
A case in point is “The Price of Anarchy in Transportation Networks,” published last September in Physical Review Letters by Michael Gastner, a computer scientist at the Santa Fe Institute, and his colleagues. Using hypothetical and real-world road networks, they explain that drivers seeking the shortest route to a given destination eventually reach what is known as the Nash equilibrium, in which no single driver can do any better by changing his or her strategy unilaterally. The problem is that the Nash equilibrium is less efficient than the equilibrium reached when drivers act unselfishly—that is, when they coordinate their movements to benefit the entire group.
The “price of anarchy” is a measure of the inefficiency caused by selfish drivers. Analyzing a commute from Harvard Square to Boston Common, the researchers found that the price can be high—selfish drivers typically waste 30 percent more time than they would under “socially optimal” conditions.
The solution hinges on Braess’s paradox, Gastner says. “Because selfish drivers optimize a wrong function, they can be led to a better solution if you remove some of the network links,” he explains. Why? In part because closing roads makes it more difficult for individual drivers to choose the best (and most selfish) route. In the Boston example, Gastner’s team found that six possible road closures, including parts of Charles and Main streets, would reduce the delay under the selfish-driving scenario. (The street closures would not slow drivers if they were behaving unselfishly.)
Another kind of anarchy could actually speed travel as well—namely, a counterintuitive traffic design strategy known as shared streets. The practice encourages driver anarchy by removing traffic lights, street markings, and boundaries between the street and sidewalk. Studies conducted in northern Europe, where shared streets are common, point to improved safety and traffic flow.
The idea is that the absence of traffic regulation forces drivers to take more responsibility for their actions. “The more uncomfortable the driver feels, the more he is forced to make eye contact on the street with pedestrians, other drivers and to intuitively go slower,” explains Chris Conway, a city engineer with Montgomery, Ala. Last April the city converted a signalized downtown intersection into a European-style cobblestone plaza shared by cars, bikes and pedestrians—one of a handful of such projects that are springing up around the country.
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7 Comments
Add CommentThis strategy should present a few headaches to people who write the software behind GPS systems.
Reply | Report Abuse | Link to thisThink about this article as you view the video 'This is imposible' on Youtube. Tear down the signs!
Reply | Report Abuse | Link to thisAs an American whose gone Dutch, I wonder how these type of theories would apply to taxation. I can't help but conclude (counter intuitively) these past 10 years that I am more wealthy as an individual now by paying double percentage points in taxes.
Reply | Report Abuse | Link to thisExample (in keeping with the subject of the article): Partially due to my extra input in the nation's budget we have in the Netherlands a greatly superior transit infrastructure. The roads are better kept, public transport is relatively excellent and everything can be reached by walkways and bicycle paths. This gives me many choices beyond my expensive car. Therefore while I remain greatly mobile my net travel expenses are less because I can choose the most cost effective form of transportation for any given trip.
Don't even get me started on health care...
In no way do I mean this comment as a political statement. I am truly curious from a scientific standpoint. Too often the discussion of taxation is clouded in a semi-religious ideology as apposed to imperial truth.
I'd love to see a good study on optimum taxation rates and government budgeting. Maybe then Washington DC could use that as a guideline to fix her potholes.
When I first moved to Tucson, AZ from the SF Bay area, I thought to myself that this place could really use an east-west freeway. Tucson has basically 1 freeway going north south on the western edge of town. As part of the project to widen the freeway they shut down all of the on-off ramps in town. Since then any north south commutes have gotten noticeably faster. And after reading this article I wonder if it would be better for them to build a Tucson bypass and shut down the freeway all together in town.
Reply | Report Abuse | Link to thisThere has been some work done in the recent past (early 1980s). It's not entirely free of ideology (right wing in this case), but if you read it with your ideology filter turned on, you'll find that it reaches some valid conclusions.
Reply | Report Abuse | Link to thisI'm referring to the debate over the earlier work of Arthur Laffer and the "Laffer Curve". The problem with it, as was the case with the earlier Keynesian economics, is that the people in charge of implementing it are unable or unwilling to understand the conditions under which it is appropriate, and when it is not, and that it MUST be adjusted as conditions change.
We are thus always stuck with policies that initially work well, but which cannot be adjusted when conditions change, as they always do, because political constituencies that benefit from the system as is will resist any change.
Come to think of it, your comparison of traffic regulation with taxation policy seems to be "right on". Those constituencies resisting changes in tax/economic policy would analogous to the "selfish drivers" mentioned in the article.
@mfcvenice
Reply | Report Abuse | Link to thisVideo "this is impossible"
http://www.youtube.com/watch?v=3n_mgFA47WQ
Socialism works great for people who agree to it.
Reply | Report Abuse | Link to thisBut no political system can function long via force and coercion.