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在拥挤交通网络中，路段阻抗不仅与本路段车流量有关，也受其它路段车流量影响.本文讨论拥挤交通网络中同时考虑本路段和其它路段流量影响时Braess’悖论的性质及在系统最优分配下新增路段的作用.利用用户平衡(UE)和系统最优(SO)条件,计算得出Braess’悖论发生时交通需求具体范围及SO分配下新增路段有意义的交通需求具体范围，研究其它路段车流量对悖论产生概率影响及对SO分配下新增路段是否起作用的影响，讨论其它路段对UE分配和SO分配网络总阻抗差距的影响.结果表明,悖论发生概率，SO分配下新增路段起作用的概率及两种交通分配网络总阻抗的差距都受其它路段不同程度的影响，这为城市交通网络规划拓宽了思路.

Braess' Paradox Phenomenon of Congested Traffic Networks

In the congested traffic networks,the link congestion is related to the flow on this link,as well as to that on other links.This paper investigates the properties of Braess’ paradox and whether the adding link makes sense under the system optimal in the congested traffic networks.Using the user equilibrium(UE) and system optimal(SO),it gives the explicit ranges of the total demand that the Braess’ paradox occurs and the adding link makes sense under SO,respectively.In addition,we investigate the influence of other links on the probability that the paradox occurs and the adding link works under SO,subsequently,we discuss the influence of other links on the difference between the total congestion under UE and that under SO.The results show the probability that the paradox occurs and the adding link works under SO,the difference of total congestion under two assignment methods are both influenced by the extent on other links,which widens theoretical ideas for the assignment of the urban transportation networks.