Research On The Calculation Method Of Urban Traffic Road Network Carrying Capacity Based On The Self-organized Criticality

Urban traffic road network is the main undertaker of transportation,the carrier of transit trips,and the core support for normal operation of urban traffic.With the deepening of the supply and demand of urban traffic contradiction,it causes issues such as traffic congestion having become the focus of social concern.Carrying capacity determines the traffic quantity and quality operation of the network,which is not only a crucial support for congestion and demand management of urban traffic,but also the evaluation index of road network planning and design.There is an important significance to establish and complete the theoretical research system and explore more optimal method of computation for road network carrying capacity while applying self-organization method to analyse law of state change of road network.Based on the relative research results of domestic and oversea experts,this paper clarifies the definition of road network carrying capacity with applying the self-organized criticality;then the research thoughts are identified to explore classification method and law of state change of road network,to introduce the computational method for the threshold of network self-organized critical state,and construct road network carrying capacity model coupled with network self-organized critical state as the constraints.The main contents of this paper are introduced as follows:Firstly,this paper refers and analyses the evolutional mechanism of self-organized critical phenomena with sandpiles model as a typical example;and on the basis of the systematically reviewing basic concept and characteristics of self-organized criticality,the paper elaborates features of road network self-organized criticality and generation of self-organized critical state,then clarifies the definition of road network carrying capacity.Secondly,a method to identify the classification of road network state and a threshold calculation model of road network self-organized critical state are proposed.This paper obtains the classification and threshold of expressway also non-expressway network state applying fuzzy C-means clustering algorithm and statistical analysis method respectively based on traffic flow data;then synthesizing above all outcomes,the paper establishes classification threshold calculation model by the ratio of single road section lane length for expressway also non-expressway network and total road section lane length for the whole road network,which clarifies road network state as four states(free-state,slightly-crowded-state,crowded-state and congestion-state);afterwards it explores law of state change of road network based on self-organized criticality,to define network self-organized critical state as the critical point of crowded-state and congestion-state,and the threshold calculation model of road network self-organizedcritical state is proposed last.Thirdly,a calculation model of road network carrying capacity is constructed with network self-organized critical state as the constraints.According to characteristics of expressway and non-expressway,the paper derives a kind of traffic volume variation-density model for road setion,in which three different models for signal upstream-signal downstream intersections,signal upstream-non-signal downstream intersections and non-signal upstream-signal downstream intersections are built for non-expressway network;after that it extends that road section model to network model,aiming to compute density of each road section;next it compares the network-density resulted by the proposed calculation model and threshold of network self-organized critical state to identify whether it is in self-organized critical state of network;Finally considering road lane length and desity of each road section,it proposes a calculation model of network carrying capacity under self-organized critical state of network.Lastly,simulation experiment and empirical research is completed in the case of Zhichun Road area in Beijing.Combined with the investigation and research data,the paper computes the threshold of Zhichun Road area self-organized critical state by proposed model;then applying results of simulation experiment by VISSIM and model solution by MATLAB to the proposed calculation model of network carrying capacity,the paper finally compares this result to the other result calculated by the primary space-time dissipative model to validate the practicability of this paper's research method.