Study On Congestion Forming、 Propagation Properties And Dissipation Control Strategies Of Urban Expressway

Urban traffic congestion has become one of the most hot-spot problems with world-wide concern. In order to alleviate and prevent urban traffic congestion, many cities in our country have brought about the planning、construction and operation on urban expressway network. Unfortunately, the desired advantages as unimpeded、fast-speed and comfortable features are disappearing, on the contrary, the urban expressway network are gradually stepping into the overall congestion critical condition with the congestion occurrences from time to time especially at the run hours, which not only brings direct economic losses but also induces inestimable consequential losses including environmental population energy consuming and traffic safety. So, research on expressway congestion is very urgent to our society’s sustainable development. While, the existing research conclusions are difficult to accurately simulate and elaborate congestion forming and propagation phenomenon, which result in aimless and passive means on resolving the congestion problem on expressway network. Therefore, detailed study to reveal the congestion forming and propagation characteristics and corresponding dispersal principles is a fundamental work to revolve congestion problems.The aim of this dissertation is to investigate the propagation characteristics and mechanism of urban expressway network and its dispersal control strategies with the aid of improved cell transmission model and dynamic stochastic traffic flow assignment theory. In detail, the main contents of the dissertation are summarized as follows:(1) Reach fitting parameters by analyzing expressway traffic flow characteristics. Comply with the summary analysis from the dual traffic characteristics on expressway network system, the traffic flow characteristics are outstand and the traffic fitting parameters are obtained based on the fundamental diagram theory and three-phase traffic flow theory, which lays the foundation for setting up the simulation model and environment to further research into congestion problem.(2) The improved variable cell transmission model with hysteresis is proposed.In order to overcome the cell length must be isometric restriction, the variable CTM model (VCTM) is represented by introducing the cell density and cell length two parameters to depict cell internal state based on the original Daganzo CTM model. Thus, the basic link module、 merged module and diverge module expressions are setup. Meanwhile, the flow-density relationship with hysteresis effect replaces the traditional simple linear traffic flow model to extend the applicability of the model. Thus, the traffic flow analysis tool is setup to research into expressway system congestion problem. The cell-based traffic congestion evaluating indicators are formulated with reference to several classical traffic congestion identification algorithms and their common used indicators.The simulation case shows that the improved VCTM model considering hysteresis can accurately capture the expressway dynamic traffic flow characteristics, which provide conditions to uncover the congestion propagation principle.(3) The improved CTM model is employed to simulate the propagation and dispersal principle of incident-based traffic congestion on expressway system.Aiming at the significant drop-down phenomenon when traffic incident occurring, the computer simulation technology is adopted to analyze the influence factors of the traffic demands capacity damage caused by incidents and delay time on traffic congestion forming and propagation characteristics based on the improved CTM model and the evaluating indicators. Further, the quantitative relationship between traffic jams recovery time and incident delay time is studied to make congestion dispersal strategies against expressway basic road link without ramp metering.(4) The improved CTM model is employed to simulate the propagation and dispersal principle of ramp-metering traffic congestion on expressway system.Aiming at the obvious influence factors of ramp distance、ramp layout and ramp control strategies on congestion propagation characteristics, the simulation case based on the improved CTM model is set up and is detailed quantified studied according to combination of different factors.(5) Research on the network dynamic traffic assignment and expressway congestion propagation characteristics.This part aims to discuss the network-based congestion propagation characteristics utilizing the dynamic traffic assignment technique. Firstly, the dynamic traffic assignment is discussed based on dynamic user optimal. It shows critical necessary and urgent to thoroughly research into dynamic traffic assignment by comparing with static traffic assignment. In respect of congestion characteristics and mechanization, the incident based network dynamic traffic assignment method is designed with the combination of dynamic probabilistic multi-route assignment algorithm and the improved CTM model. Simulation cases are employed to achieve the dynamic traffic assignment process and further discussion on the congestion propagation characteristics on incident-based network, which caused traffic flow impedance varying with congestion propagation.In the finality, future research directions are brifly discussed and recommended.