Archive for August 29th, 2008

Self-Organized Traffic Flow

One of the oft-revisited themes in the book is that individual actors in traffic don’t often have an idea of what might be best for traffic as a whole. In a great piece in the New Scientist (sub required), “Why Complex Systems Do Better Without Us,” Mark Buchanan (whose book The Social Atom is high on my reading list), writing about the traffic physicist Dirk Helbing, makes the following point:

“Although the behaviour of individuals is often simple, the collective patterns to which it leads can be counter-intuitive, making common sense a faulty guide to what might happen. For example, it is generally true that traffic jams become more likely as traffic density increases. It’s not always the case, though, as Helbing’s group has shown.

Consider a two-lane road carrying both cars and trucks, where the cars are moving faster on average. At low traffic densities, the cars have plenty of space to overtake and can easily pass the trucks. As the traffic density increases, drivers find it more difficult to overtake because other vehicles are in the way. However, evidence from simulations and real traffic flows shows that at a critical density of traffic, the obstruction to lane-changing begins to have a beneficial effect. Because drivers tend to stay in one lane, they disturb the flow of traffic less, leading to a higher total throughput of vehicles.”

Another interesting strand in the piece is the notion that allowing traffic lights to control themselves would improve traffic flow. Instead of set timing patterns or even merely “synchronization,” the lights judge conditions for themselves and make constant adjustments (this is essentially the high-tech version of Hans Monderman’s “bottom-up” traffic scheme in the Netherlands). This is one of the next frontiers of traffic, and I’ve had described to me fascinating systems employing “genetic algorithms” for things ramp meter lights — the ramp meters would in essence keep learning over generations of traffic flow, evolving into smarter systems.

Of course, the new light schemes run the risk of not making sense to the individual driver, as Buchanan notes: “Nonetheless, the behaviour of the lights doesn’t generally fit with human notions of what ought to be efficient. “How long lights stay green is unpredictable,” says Lämmer. Yet the average journey times go down and become more predictable.”

The piece includes what may come to be a mantra: “Being in control, it seems, may increasingly demand being a little out of control.”

Posted on Friday, August 29th, 2008 at 4:45 am by: Tom Vanderbilt
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Traffic Tom Vanderbilt

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.

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April 9, 2008.
California Office of Traffic Safety Summit
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May 19, 2009
University of Minnesota Center for Transportation Studies
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Driving Assessment 2009
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June 26, 2009
PRI World Congress
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Association of Transportation Safety Information Professionals (ATSIP)
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California State University-San Bernardino, Leonard Transportation Center
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Yale University
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Eero Saarinen Lecture

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International Bridge, Tunnel and Turnpike Association (Organization Management Workshop)
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Royal Automobile Club
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Wisconsin Department of Transportation’s
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American Association of Motor Vehicle Administrators
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Wednesday, October 26, 2011
Attitudes: Iniciativa Social de Audi
Madrid, Spain

April 16, 2012
Institute for Sensible Transport Seminar
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April 17, 2012
Institute for Sensible Transport Seminar
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April 19, 2012
Institute for Sensible Transport Seminar
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January 30, 2013
University of Minnesota City Engineers Association Meeting
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January 31, 2013
Metropolis and Mobile Life
School of Architecture, University of Toronto

February 22, 2013
ISL Engineering
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March 1, 2013
Australian Road Summit
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New York State Association of
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August 18, 2013 “Ingenuity” Conference
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TransComm 2013
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Officials’ Subcommittee on Transportation
Grand Rapids MI



August 2008

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