可以自组织的交通信号灯

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图1 自组织交通信号灯的调控机制

       

       右图显示的四向多车道十字路口运行了自适应周期的信号灯。左图显示，随着总体交通入流密度（这里表示为利用率u）的增加，信号灯最佳序列和时间间隔也在发生变化（来源：Dirk Helbing，苏黎世联邦理工学院）。

 

       在德国德累斯顿市的繁忙市中心，有13个混杂着电车轨道和人行横道的十字路口，对于这一区域交通网络的模拟结果显示，自组织的信号灯可以显著减少包括步行在内的所有交通模式的等待时间。同样的原理也适用于其他交通控制措施，例如速度限制：允许车辆根据实时的交通流情况调整速度可减少拥堵和延时。

 

以下为英文原文：

Improving traffic flow is not so much a matter of imposing particular behaviours as of creatingthe conditions under which the traffic can spontaneously organize itself in the most efficient manner. That philosophy doesn’t always sit easily with managers and planners, but it is looking increasingly to be the best way to approach all manner of social phenomena: to relinquish top-down control in favour of a faith in the bottom-up capacity of complex systems to find their own efficient modes of behaviour, given the opportunity.

This is illustrated by a reconsideration of how to coordinate traffic lights. The normal approach is to synchronize a periodic sequence of on-off times for aseries of lights at a cluster of intersections. But there is no reason to suppose either that the best sequence is strictly periodic or that it has toremain the same regardless of the traffic conditions. It turns out to be better to allow each individual traffic light to respond adaptively to the flow conditions at any moment.

The notion of allowing traffic signals individual autonomy could sound like a recipe for disaster– why should there be any guarantee that what is ‘best’ for one intersection will also suit what is happening at the others? However, if each signal issupplied with information not only about the traffic at that particularjunction it but also about the traffic coming from neighbouring junctions, thissharing of information can enable the system as a whole to find more effective, flexible solutions at any moment than are available from an insistence on regimented periodicity.

The idea is that traffic sensors placed a little before an intersection feed information about the incoming flow to each individual light-controlling system. This makes it possible to calculate the expected delays, and corresponding ‘trafficpressures’, at different parts of the network. Priority for green signals is then given to those parts experiencing the greatest pressures. In this way, the traffic itself controls the lights, rather than vice versa. Chance fluctuations,such as temporary lulls in the traffic on some routes, can be exploited torelieve congestion elsewhere. The behaviour that emerges can in fact look surprisingly synchronized, for example in the appearance of ‘waves’ of green lights that travel through the network.

Simulations of traffic flow on a network where autonomous lights are coordinated in this way show that overall average delays can be reduced by 30–40% relative to today’s state-of-the-art conventional control methods, and that the travel times for individual vehicles through the network actually become more predictable.

A simulationstudy of a real-world urban network – 13 intersections in the busy city centre of Dresden, complicated by tram lines and pedestrian crossings – has shown that self-organized traffic lights can significantly reduce the waiting times for all the modes of transport, including pedestrians. The same principle can be applied to other traffic-control measures such as speed limits: allowing them to adapt to the prevailing flow conditions can reduce congestion and delays.

 

参考文献：（英）菲利普•鲍尔著, 韩昊英译, 赖世刚校. 社会为何如此复杂：用新科学应对二十一世纪的挑战. 北京：科学出版社,2015.

本文作者在原书的基础上，重新撰写了文字。

 

目前为浙江大学城乡规划学和公共管理学的教授、博士生导师，学术背景为建筑学、城乡规划学和公共管理学，曾在清华大学、日本东京大学、韩国首尔国立大学和加拿大多伦多大学攻读学位或访学研究。韩昊英从小生活在城市，热爱城市的历史和文化，喜欢观察和体验多样的城市生活。