Congestion Identification Of Urban Transportation Network

The urban transportation network is a complicated system which is composed with many road sections and intersections, thus, the traffic congestion is prevalent in the world. In order to resolve the question, the first thing is to identify it, however, even till now there is not a uniform standard.On the basis of existing traffic congestion identification and relevant studies, A theory is advanced in this dissertation to identify traffic congestion from part to whole which happens in urban transportation network, including congestion identification of road section, intersection, urban transportation network. The main contents of this dissertation are as follows:(1) The data acception techniques for traffic flow are introduced and the fundamental characteristics of traffic flow are expounded. First several definitions of traffic congestion are introduced. Second, the causation of recurrent congestion and non-recurrent congestion are given respectively. Third, the traffic congestion of urban transportation network is analyzed from the aspects of time, place, causation and special distribution.(2) When traffic flow is lower than road capacity, the congestion identification of road section has been modeled, which is related to the triangle area enveloped by free speed, speed and density. When traffic flow is higher than road capacity, after studying fitting function of the time continuance, lognormal function is chosen to forecast traffic condition in this dissertation.(3)The congestion identification of intersection is modeled. The model of input rate in the downstream intersection is built, which changes with the output rate in the upstream intersection. Considering the numbers of cars at the beginning of signal cycle on intersection, the model of intersection delay is built under three conditions(under-saturated, critical-saturated, over-saturated). The average input rate is used as the arrival rate, the ratio of real average vehicle delay to average vehicle delay under critical-saturated condition is considered to be the congestion level of intersection.(4)By the method of summation with weight of road section congestion and intersection congestion, the congestion identification of the unit which refers to the road section and its downstream intersection is modeled. The average of congestion of all units is the congestion level of urban transportation network. The two-fluid theory is used to verify the weights. In order to make the path congestion balanced, the stochastic user equilibrium model is built, the equivalence and exclusive of which are proved, and the arithmetic for the model is given.