Study On Urban Road Network Capacity

Along with rapid developing of urban growth and increasing of urban population and vehicle population, traffic demand and traffic pressure are increasing gradually. Therefore, the traffic jam has become a problem to be faced and solved. Road network is urban physical infrastructure, its service quality is crucial for social sustainable development, quality of life and image of city. So it is very important to research the capacity of urban road network for developing our traffic and constructing harmonious and smooth traffic.On the basis of analyzing and summarizing the existing related principles and methods of road network, according to the inconsistent definition of urban road network capacity, considering the main factors and combining research purpose, the new conception of road network capacity is defined based on the service level. Moreover, the index and division standard are set up for judging the service level of urban road network. This work lays the foundation for measuring urban road network capacity.Assume that each traveler can acquire real-time traffic information accurately. In accordance with the influence of traveler's route choice behavior and characters of various traffic assignment models, the model of urban road network capacity is established based on user equilibrium (UE) traffic assignment considered the influence of intersection. Furthermore, the first order necessary condition for optimal this model is obtained by use of Kuhn-Tucker theorem and the convergence theorem is put forward which is used for calculating road network capacity in this paper. Simultaneously, the numerical example verifies that this road network capacity algorithm has less calculation process than existing algorithm and reduces calculation times of shortest path. Consequently, the efficiency of road network capacity algorithm is improved greatly.While the dynamic traveler information system is imperfect, traveler chooses route only according to his own estimation. Thereby, the urban road network capacity model based on stochastic user equilibrium (SUE) traffic assignment is established to deal with this situation. By analyzing the major methods of SUE traffic assignment, some disadvantages that affect them to practical application are fount. So, the conception of efficient path set is redefined based on path effect degree which is proposed according to the degree of one path affecting traffic volumes on other paths, and calibration algorithm of path effect degree parameter for efficient path set is design. In order to increase the quantity of elements in efficient path set at initial stage and decrease the calculation process, a genetic algorithm (GA) is designed to find the initial efficient path set. Furthermore, the algorithm of this road network capacity model is put forward based on efficient path set. Besides, effect degree parameter of efficient path set is analyzed and the road network capacity models based on UE traffic assignment and SUE traffic assignment are contrasted and analyzed through a numerical example. In real traffic network, the capacity of link or intersection is not constant, but rather fluctuation within some bounds. Consequently, under this condition, the fluctuation regulation and fluctuating range of road network capacity are apparently necessary to be well-studied. Accordingly, the equilibrium condition expression is brought forward as the principle of path choice under uncertain environment. According to this principle, the road network capacity models based on UE traffic assignment and SUE traffic assignment under uncertain environment are established respectively. Considering different disposal methods of uncertainty variable, two algorithms are designed based on crisp equivalents and computer simulation. In addition, the road network capacity models based on UE traffic assignment and SUE traffic assignment under uncertain environment are contrasted and analyzed.For current city, the increase of urban population and vehicle population results in the increase of traffic demand and traffic pressure. Accordingly, current road network capacity may not adapt the demand of economy and social development. In order to meet the traffic demand, link or intersection in traffic network needs to be extended. So, on the base of putting forward the contribution degree conceptions of link and intersection, the contribution degree based capacity expansion model is set up with fixed cost and its algorithm is also designed.In daily urban traffic activities, traffic broken on link or intersection is common because of short time traffic control or contingency and influences urban traffic significantly. However, different link or intersection broken may cause different loss of road network capacity. Therefore, the definitions of vital link and vital intersection are given to describe the capacity loss. Furthermore, the respective road network capacity models and algorithms of vital link and vital intersection are provided to analyze bottleneck of road network.By extensive analysis of the numerical example, some valuable conclusions are acquired which can provide the theoretical basis for traffic control departments to set suitable policy measures, ease the traffic pressure, guide resident trips, decision investment and draw up emergency decisions, etc.