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拥挤收费的主要原因是拥挤外部成本的存在。城市道路交通拥挤外部成本的定性、定量分析是城市道路拥挤定价的基础。文章首先分析了城市道路交通拥挤的产生机理，即出行者忽视拥挤负外部性的存在而盲目加入拥挤队伍；然后明确了城市道路交通拥挤外部成本的构成：额外时间成本、环境污染成本、交通事故成本和燃油消耗成本，并研究其定量计算方法；最后应用实际数据进行了计算分析，证明了该方法的可操作性。该项研究为实施城市道路拥挤收费等交通需求管理策略提供了基础和依据。

Method Research on Measuring the External Costs of Urban Traffic Congestion

The main reason for congestion pricing is the external cost of congestions.Qualitative and quantitative analyses of the external cost which urban traffic congestions bring are the base of congestion pricing.Firstly,this paper analyses the production mechanism of urban traffic congestions: travelers overlook the negative externality of urban traffic congestions and join in the congested queues.Then,the external cost of traffic congestions are divided into four parts: extra travel time cost,environmental pollution cost,traffic accident cost and fuel consumption cost.Consequently,an intensive study of the quantitative measurement for those four kinds of external cost is made.Also,a sample case is introduced to prove the feasibility of this method.It supplies a basis for the implement of urban road congestion pricing and other travel demand management strategies.