Investigation On Interaction And Characteristics Of Traffic Flows In Urban Elevated Road-Ramp-Ground Road System

The rapid development of the automobile industry and the relative lag of the road construction have constituted a prominent contradiction all over the world, particularly, in most of large cities. To cope with it, elevated roads have been built in many cities both at home and abroad. However, traffic jams frequently appear on elevated roads immediately after the completion of their construction. The awkward situation mainly results from the planning bug or the unsuitable control, apart from drastic increase in transportation demand. Elevated roads, ramps and ground roads are closely interconnected in three-dimensional urban traffic networks. Based on the field measurements, in this dissertation, by using the macroscopic and microscopic methods, i.e., the hydrodynamic models and cellular automaton models for traffic flows, the relations among the three interacting parts were investigated. The mathematical modeling and numerical simulation were conducted for the sections of elevated roads and for the interaction of elevated roads and intersections on the ground. After having analyzed the complicated dynamic behavior on the elevated roads, some suggestions were put forward for the transportation planning and management. The contents of the dissertation are as follows:(1) By combining manpower survey with the video recording, a series of field measurements were conducted on several sections of the elevated road system in Shanghai City and then the main characteristics of the elevated road traffic flow were captured. By means of data processing and analysis, two speed-density relations were established, which are suitable for the free flow and the congested flow respectively. And thus two important parameters, namely, the free flow speed and the jamming density, were determined. The fundamental diagram obtained from the measured data reveals three distinct traffic phases.(2) With the Wuning Off-Ramp of the Inner Ring Elevated road in Shanghai City as a representative case, meticulous observations were carried out on traffic flow at the intersection near the off-ramp. And it was found that the "squeezing" effect ofright-turning vehicles from the intersecting main road on the straight motion of vehicles from the off-ramp is the main reason of the existing traffic jam. A modified 1-D pipe-flow model was established by introducing a source term into the continuity equation and a relaxation term into the motion equation in Wu Zheng's model. With the modified model, numerical simulation was performed with special attention to the disturbing effect of right-turning vehicles. The results agree quite well with the observed data. The analysis shows that the "squeezing" effect, which exacerbates with the increasing number of right-turning vehicles, is the principal cause of congested traffic at certain intersections. The inappropriate design and construction of ramps in front of busy crossings enhances the congestion. Thus, installing the right-turning traffic lights may be a promising way of solving the problem.(3) There exist severe problems in the transportation on elevated road system in Shanghai City, such as frequent congestions or jams on the elevated roads and their ramps. For this reason, measures of controlling the on-ramp traffic with timing signals were suggested in this dissertation. The reasonable timing scheme was recommended for signal controlling. On the basis of an anisotropic hydrodynamic traffic model developed by our research group, a ramp-effect term was introduced in the motion equation and traffic flows on the elevated road sections near the on-ramp were numerically simulated. The results show that signaling control of on-ramp is helpful for the improvement of traffic on the elevated roads. We also found the best timing scheme after comparison among six choices of signaling period.(4) The gear-alternating regulation was first actualized at the interfluent location of on-ramps in Shanghai elevated roads, which was theoretically studied in this dissertation. Different traffic flow models were established for the cases with and without the alternate running rule based on the FI cellular automaton traffic model. With the models, the traffic behavior at the interfluent location of on-ramp was investigated and some results were concluded. When there are many inflowing vehicles on the elevated road and ramp, the traffic situation on the elevated road with the alternating regulation is much better than that without the regulation; when there are less inflowing...