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发表于 2008-4-2 02:10:05
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[新闻快迅]不稳定性：塞车的固有物理诱因
Phased by Traffic Jams?
http://sciencenow.sciencemag.org/cgi/content/full/1997/1105/3
5 November 1997
Traffic jams sometimes start for no apparent reason and can last for hours. Now, after observing a notoriously choked stretch of autobahn, two German researchers think they understand better why even a minor slowdown on a packed highway can rapidly trigger long-lasting gridlock: Traffic at times appears to act like a substance rapidly changing from, say, a gas to a liquid. Their findings, to appear later this month in Physical Review Letters, could lead to more accurate highway traffic predictions.
Twenty-two years ago, Joseph Treiterer of Ohio State University, Columbus, suggested that traffic flows can resemble phase transitions--changes of state such as the condensing of steam into water. To investigate traffic transitions, Boris Kerner of Daimler-Benz in Stuttgart and Hubert Rehborn of Heusch/Boesefeldt, an intelligent transport systems firm in Aachen, used magnetic induction loops in a three-lane stretch of southbound highway near Frankfurt to monitor the number and speed of cars traveling in each lane.
Based on their observations, the duo describe three states of traffic on busy highways: "free flow," in which traffic is light enough that drivers can freely change lanes and pass other cars; "synchronized flow," in which the roads are so clogged that drivers can';t pass, but can still move; and jams. Kerner and Rehborn found that surges of vehicles joining the highway disrupted the traffic flow enough to initiate the jump from free to synchronized flow within minutes. After being established by what might be only a brief disturbance, the synchronized flow could last hours.
Kerner suggests that heavy traffic behaves like supercooled steam, in which it only takes a molecular "seed" to trigger millions of molecules to condense into water. A highway seed could be the sudden rush of drivers on an entry ramp, or drivers already on the highway slowing to admire the scenery, Kerner says. These apparently isolated disturbances "can cause a phase transition to a state with very high density of vehicles which stays for hours on the road," he adds. Once synchronized flow is established, the researchers found, free-flow driving resumed only when the traffic volume had dipped to about 50% of pretransition levels.
The findings could be used to help develop traffic forecasting and intelligent transport systems, Kerner says. Incorporating phase transitions into traffic models will be "a real challenge," warns Stefan Krauss, a traffic researcher at the German Aerospace Center in Cologne, because modeling efforts so far have focused on average traffic levels rather than jumps between traffic states. But the new work, Krauss says, offers the prospect that "simulations [could] become good enough to give a good forecast of things like road capacity."
以上给出了 ScienceNOW Daily News 上的另一个涉及交通堵塞的物理机制阐释。
以下除了标题均有Google的语言工具翻译而成，希望以后有时间在慢慢翻译，呵呵！
交通堵塞诱发的相变
交通拥堵，有时开端，并没有明显的理由，并可以持续好几个小时。现在，经过观察着呛舒展的高速公路，两名德国研究人员认为他们更好地理解，为什么即使是轻微放缓对满满公路可迅速引发长期的，持久的困局：交通有时似乎像一种物质迅速变化的，也就是说，天然气成液态。他们的调查结果，出现在本月晚些时候在物理评论快报，可能会导致更准确的公路交通预言。
二十二年前，约瑟夫treiterer俄亥俄州立大学，哥伦布，他建议交通流动可以类似于相变-变化的国家，如冷凝式蒸汽排入水域。调查交通过渡，鲍里斯kerner的戴姆勒-奔驰公司在斯图加特和H ubertr ehborn的h eusch/ b oesefeldt，智能运输系统公司在亚琛，采用磁感应线圈在一个三线的一段公路南行法兰克福附近的监测数量和速度汽车行驶在每个车道。
根据他们的观察，两人形容这三个国家的交通繁忙的公路上说： "自由流通" ，其中交通是重量轻，因而驾驶者可自由变更车道，并通过其他车"同步流动， "中，道路堵塞，使驾车人士可以不通过，但仍可以提出;拥堵。 kerner和rehborn发现潮的车辆参加公路中断交通流足以启动跳转，从免费到同步流动分钟。成立以后，由什么可能只是一个短暂的干扰，同步流动，可以最后几个小时。
kerner显示，在交通繁忙的所作所为一样，过冷蒸汽，其中只需要分子"种子"引发百万计的分子凝聚成水。一条公路的种子可能是突然司机就进入机坪，或司机已经在高速公路上减速欣赏美景， kerner说。这些看似孤立的动乱" ，可以引起相过渡到一个国家，具有很高的密度的车辆停留几个小时就道， "他补充道。一旦同步流动，是建立后，研究人员发现，自由流动的驱动恢复，只有当交通量已下降至约百分之五十的pretransition水平。
研究结果可以用来帮助我们发展交通预报和智能交通运输系统， kerner说。把相变到交通模式将是"一个真正的挑战， "警告斯特凡克劳斯进行了交通研究员，在德国航空航天中心在德国科隆，因为造型的努力，到目前为止，已集中于世界平均水准，而不是跳跃之间的交通状态。但新的工作，克劳斯说，优惠的前景，认为"模拟[可以]成为好足够让一个好预测的事物一样，道路容量" 。 |
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