Studies On The Complexity Of Topology Structure In The Urban Traffic Network

As an important component of traffic systems, urban traffic is not only a basic part to bear the human activities, but also the main supporting condition for the city prosperity, ordered and high-speed developments. However, increasing traffic problems have affected the city's economic construction and the operating efficiency, even do much harm and inconvenience to our life and work. Therefore, traffic problems have become a great bottleneck of the urban sustainable development.It is well known, the urban traffic is a classic, exoteric and complex system, and its running rule is also intricate. Under the new situation, in order to alleviate traffic problems in large cities and build a harmonious transportation system, it is necessary to develop theoretical and applied research with complex systems methods through combining the principle of system sciences and the interdisciplinary theoretical system. On the other hand, we should recognize and understand the evolution and internal operating mechanism of urban traffic network from the whole and macro viewpoints.Complex networks theory provides a new view and method for studying the system complexity. The finding of small-world effects and scale-free property has attracted a great deal of attention to the complex network structure and dynamics in recent years, which raises the science awareness of the real world. With the in-depth research for complex networks, it has infiltrated including sociology, biology, physics, economics, computer science, as well as transport and other areas.The key problem of complex traffic networks is to analyze their structure complexity including the topology complexity and the characteristics in different topologies, which is also a foundational theory of the urban traffic. The urban traffic network has some similar topology characteristics as other complex networks. However, many different properties are found in the urban system, such as autonomous and selective behaviors. Moreover, it has become a commonsense that we should study the urban traffic systematically from road lane to road network. In addition, adaptability and dynamic characteristics are also important properties, which mean that their topology structures are not fixed and unchangeable, and they will evolve with time under the external and internal force drive.This dissertation, from the points of complex network theory and network optimization, studies the complexity of topology structure for the urban traffic network. The main contents of this dissertation are summarized as follows:(1) Firstly, by combining the user equilibrium assignment with the complex network theory, we study the effects of network topology on the traffic network. Then, the interactions between the network topology and traffic flows are researched. Further, the optimal traffic topology is evaluated based on the complex network perspective, and the relationship among degree distribution, traffic demand and traffic congestion is analyzed.(2) Secondly, cascading failures are an important branch in the dynamics of the complex network. In the thesis, we firstly propose three models, different removal strategies cascading failures model, edge-node-edge cascading failure model and dynamical node-capacity update cascading failure model, to capture the dynamics of cascading failures in the urban traffic network. Moreover, simulation tests are given in different network topologies.(3) Thirdly, many economic problems exist in the urban traffic, e.g., the upper bound of the efficiency loss for user equilibrium and the economical method to alleviate the traffic congestion. The efficiency loss for user equilibrium in different topologies with nonlinear cost functions and the general law under the traffic congestion condition are investigated. Results show that the upper bound of the loss is limited and ordered. And there exists a higher resistance to the free competition for homogenous networks than that of heterogenous networks. Based on these results, the bottleneck identification and the strategy to alleviate the traffic congestion are proposed.(4) Then, a capacity assignment model is established to improve the network's robustness. Then, we extend the model to traffic networks and propose a new method to measure the link importance by considering the efficiency of traffic networks. The link-importance-based capacity assignment model with limited resources and profits functions to resist the cascading failures are given. The power-law form of link-importance distribution and the relationship between the profit function and assignment parameter are analysed.(5) Finally, the complexity and robustness of Beijing transit network and Chinese highway network are studied through simulating and attacking experiments.