Research On Urban Traffic Network State Evaluation

In recent years, in order to alleviate congestion which is more and more serious, the managers used the advanced theoretic or technical method to manage and control city road as well as highway.Traffic can't be managed effectively using ITS without the information of urban traffic network state. The Advanced Traffic Management systems in the ITS is built on obtaining of the update information of the traffic network state, on the basis of this, making the decision of traffic management and travel plans,in order to take full use of the space-time resources. When the network operating efficiency improved,the growing demand of the traffic could be fulfilled through the enhancement of the road safety and using efficiency,without building new roads.The paper researched on the urban traffic network state estimation ,whick is the crucial issue in urban traffic management system.Start from analysising the state of the intersection and road,the paper focus on choosing of the evaluation parameters and establishing the evaluation function of the traffic network state. The content of this paper is composed by the following components, the specific contents are as follows:In Chapter One, research background, significance and content were depicted. In Chapter Two, the sate of the road was studied. First,analysis the parameters of the traffic flow,which reflect the traffic flow characteristics.But some parameters can not reflect the operations of the traffic flow individually ,such as the volum of traffic flow,the same value represents two distinct status. Subsequently, the basic characteristics of urban road traffic flow was analysised in this chapter. Compared to highways, the distribution of urban roads traffic flow were uneven ,that is, the density and the speed of the flow has a great difference in a different location of the road. In this part, urban road traffic state is divided into congestion and smooth. The characteristic of congestion and smooth traffic flow was also given in this part. Finally, on the basis of the former analysis of traffic parameters ,choose the speed of road as the main parameters of the state estimation, and study the use of multi-detector laid method to estimate the average driving speed on the road.In Chapter Three, the sate of the intersection was studied.First,several important parameters that reflect the operating efficiency of the intersection was analyzed, including the capacity of the intersection, saturation and the length of the queue. This part focus on the method of calculating the length of the queue in front of the intersection,as the the length of the queue is the basic evaluation parameter of this paper. Traffic wave theory is used to create real-time queuing model in this chapter, and Gelinbei model which is suitable for describe high-density traffic flow is used to modify it. In the new model, the independent variable is the density of the traffic flow.In the last of this part,the state of the intersection were devided into smooth traffic flow, the general overcrowding and severe overcrowding state.The indentification method of fuzzy mathematics was used to evaluate the state of the intersection.In chapter Four, the evaluation of urban traffic network.was studied. In the base study of the road and intersection state,the running speed of road and the proportion between the lenth of the queue and the lenth of the section was chosen as the basic parameter for the evaluation of the urban network.. This chapter first establish the objective function through these two basic parameters, to reflect the overall road network state. And define the state factor of the traffic network as the impedance of traffic running unblockly. The accessibility between any two points can be counted according to the definition of impedance. The accessibility reflected the status of the current two node,also the overall accessibility of the network could be evaluated.In the end of this part,the definition of the connectivity under a cut-off value was given. The the state of the road section.could be evaluated through judging the section is conneted or not. Using the depth-first graph search arithmetic can judge the spatial distribution of the not connected sections.In the fifth chapter, the author sums up the dissertation, looks back all the course and development of the research and enumerates all the problems that need to be further studied.