Go With The Flow
Dresden, Germany (SPX) Nov 16, 2007 Traffic flows account for as much as one-third of global energy consumption. But unconventional changes in managing traffic flow could significantly reduce such waste and lower harmful CO2 emissions, says Dirk Helbing. Dr. Helbing, Professor of Sociology at the ETH Zurich Chair of Sociology, a specialist in modelling and simulation, supports his claim with a recent study called 'Efficient Self-Control of Traffic Flows in Urban Networks Using Short-Sighted Anticipation'. Professor Helbing and co-author, Stefan Lammer of the Institute for Transport and Economics at Dresden University of Technology, propose a self-organized control system for traffic lights that could improve vehicular traffic flow by up to 95 percent. The system relies on the joining of two distinct strategies.
Traffic light system antiquated The disadvantage of this strategy, especially today, is that the more traffic lights there are to coordinate, the more difficult it is to optimize control of the lights. Why? The dilemma is well-known: the larger the number of nodes, or lights, in a system the more computation is necessary until finally computational time "explodes". "Even for normal-sized cities, super computers are just not fast enough to compute all of the different options that exist for controlling traffic lights. So the number of choices actually considered by the optimization program is significantly reduced," says Professor Helbing. Most traffic lights, therefore, continue to be programmed offline, regardless of the realities of the road. Unfortunately, "the variation in the number of vehicles that queue up at a traffic light at any minute of the day is huge," Professor Helbing says. None of this variation is considered when optimizing for typical Monday or Friday traffic volume curves. "You are optimizing for a situation that basically is true on average but that is never true for any single day or minute: essentially for a situation that never exists. Plus, even adaptive traffic lights in modern control schemes are usually restricted to a variation of cycle-based control."
One strategy is not enough Another component, a stabilizing strategy, was then studied. This strategy cleared traffic when it reached a critical threshold, but it was inconsistent with travel time minimization. Unlike the optimization strategy, the stabilizing strategy performed poorly at all volumes. On its own, it too could not compete with today's traffic light control systems. However, "it turns out that the two strategies properly combined perform better than today's traffic light controls at all traffic volumes. So the combination of two inferior strategies can perform much better - if we do it right," Professor Helbing says. Simulation tests show the combined strategies work well. With non-periodic - not cyclically repeated - traffic lights releasing long traffic queues, travel time even becomes more predictable. Flow is kept stable, fuel consumption and emissions are reduced.
Succes depends on motorists In Asian countries, where infrastructure is still being built, is where Professor Helbing thinks investment in the combined strategies might first take place. In Europe the "pain and pressure for change may still not be great enough". In the end, cost will be a determining factor. The new technologies will have to show that they are cheaper to run than the present system.
Testings ahead Politicians need to be informed of the options. And the traffic light systems themselves must now be tested through practical application. Professor Helbing is nonetheless optimistic that they will out-perform the systems of today. "What we don't know is how big an advantage the news systems will be. But all the facts point to decentralised traffic control. This will be the paradigm of the future." Related Links Car Technology at SpaceMart.com
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