Research Of Dynamical Properties Of Traffic Flow Based On Complex Network Theory

With the rapid development of economy, the scale of urban road network is larger and larger, but at the same time, the number of cars is growing sharply. With considering the current urban traffic conditions, the development of urban traffic system has not satisfied people’s growing traffic demand, which results in the traffic problems, such as traffic congestion, traffic accidents, road congestion and other issues are frequent. From the perspective of sustainable development, the city scale impossible unlimited expansion, will be more and more limited land resources, increasingly scarce, how to under the condition of limited road resources to alleviate urban traffic congestion and improve the carrying capacity of road network has become the focus and hotspot in the research of the related problems.To reveal the inner mechanism of the urban traffic flow, studying the topological structure properties of urban basic road networks and other complex systems such as public transport system, and researching the dynamical properties of road traffic flow and network traffic flow, which are helpful to explore the traffic guidance strategy for diminishing the traffic congestion and enhancing the throughput of the entire urban street network. Thus, analysis of the complexity of street network and traffic flow is very important to urban traffic problem research.On basis of this, the structural characteristics of urban traffic networks and the dynamical routing algorithms are deeply studied in this thesis. Combined with GIS and complex network theory, the topological structural properties of urban traffic network are studied systematically by introducing the concept of multi-granularity; the affect of implementing one-way transmission controlling of traffic flow on the whole network’s traffic process is analyzed for various network models; deeply studying the generation mechanism of traffic congestion, the interaction principle between nodes in traffic transmission is described and defined by using the gravitational field theory, so as to propose a dynamical routing algorithm based on node gravitational field. Specifically speaking, the main research contents and achievements of this thesis are as follows:1. Combined with the GIS network analysis method and the complex network theory, the construction principle of complex traffic network model is studied beneficially. It found that the road networks for different scales all follow the small-world and scale-free properties. By introducing the concept of multi-granularity, the multi-granularity complex network of urban roads is established, and the topological complexity of the multi-granularity complex road network and the reliability of the whole urban road network are researched. The empirical research shows that the multi-granularity complex road network has the scale-free characteristic and is more helpful to accurately study the robustness and vulnerability of the urban road network.2. For further research the complexity of urban traffic system, the urban public traffic system is study. From the point of view of the passenger’s travel station choosing cognition, this dissertation introduces the concept of station service area which can be determined by Voronoi graph. Based on this, the public traffic service reliability index and corresponding attacking strategy are defined respectively for the public traffic station network and the public traffic line network. Experimental results show that, the suggested reliability analysis method of the public traffic system can more accurately describe the robustness and vulnerability of the urban public traffic system.3. The affect of implementing local one-way transmission of traffic flow on the whole network’s traffic process is analyzed. With the connection degree and betweenness as constraint conditions, two constraint models for the one-way transmission of traffic flow are defined. By taking the ER random network, WS small-world network and BA scale-free network for experiments, an important conclusion is drawn:to implement one-way transmission of traffic flow for serious congestion nodes can significantly enhance the transmission capacity of the ER random network and WS small-world network, and can reduce the congestion degree of the whole network, but cannot effectively impove the transmission capacity of the BA scale-free network. These resuts support important decision-making reference for the guidance controlling of urban traffic, because most of the urban traffic networks are proved to obey power-law distribution that means the urban traffic networks are mostly scale-free networks.4. Using the theory of gravitational field, the interaction between nodes during the traffic flow transmission process is studied, and the gravitational field equation inspired by node is defined. Based on the suggested equation, this dissertation defines the gravitation function for computing the attraction of any transmission path on the packet that can be described as the average of the gravities of all the nodes on the path. Then, a dynamical routing strategy is proposed as follows:calculating the gravity of the shortest path from each neighbor to the destination, and choosing the neighbor on the shortest path with maximum gravity as the next routing node. Simulation results show that this routing algorithm greatly enhance the transmission capacity of the whole network and effectively diminish the congestion situation of the network.5. For further research on the gravity mechanism of the routing protocol in complex networks, the concept of routing awareness depth is introduced, the calculation formula of the gravity of the transmission route for the packet within the routing awareness depth is defined, and also the corresponding routing strategy is presented. The experimental results uncover an important dynamic phenomenon, that when the value of routing awareness depth is greater than the average path distance of the network, the routing strategy can significantly improve the region of the network, and then the transmission efficiency will not change with increasing the routing awareness depth, the network’s transmission capacity reaches steady state.6. From the standpoint of gravitation equilibration, using the idea borrowed from the standard deviation, a critical gravitation may be existed under the interaction of attractions between nodes, and the routing selection process may be more efficient based on this critical gravitation. On basis of this assumption, a mathematical model which can reflect the dispersion degree of nodes’ gravitations is established, and then a new gravitatiaonl field routing algorithm is proposed based on this mathematical model. Experimental results shows that this routing algorithm considerablely enhance the transmission capacity of entire network and efficiently balance the traffic load of network. To some extent, the performance of this algorithm is superior to the routing algorithm based on the average gravitation of path’s nodes.