Improvement Strategies Based On Variable Limit Speed And On-ramp Control For Weaving Segment Of Expressway

With rapid development of national economy and acceleration of urbanization, the construction of expressways in China has entered into the phase of rapid development. As the same time, congestion of expressways has been a serious problem of urban development. Expressway is a complex system. Because of land use restriction, urban expressways always have structural problems which lead to capacity drop of weaving segments. The capacity drop is one of reasons for congestion of urban expressways. The most of existing researches aim to analysis of mechanism of capacity drop of isolated merging area and how to prevent this phenomenon. The researches for capacity drop of weaving segments are few. With the development of automatic control technology and computer technology, acquisition of real-time traffic information has become possible, which lays a solid foundation for traffic control technology. Traffic control strategies are more and more widely used for release of congestion. This paper's object is three weaving segments of Shuangqiaomen expressways in Nanjing. The purpose of this paper is to analyze their capacity drop and propose the optimal control scheme, which is the decision basis for traffic administrative department. The following contents are what this paper will research:First of all, this paper researches capacity drop of weaving segment of expressway. With data from videos and in-and-out method, flow, speed and desity are received. Then rescaled N-curve and curve of speed and density are used to confirm the capacity drop. Calculation of capacity in different phases and confirmation of traffic density when capacity drop happens lays the foundation of subsequent research of this paper.Secondly, this paper builds the simulation model based on variable and on-ramp control with PARAMICS. The geometrical characteristic and traffic condition of Shuang qiaomen segment of the inner ring expressway in Nanjing are introdued carefully. Based on the real condition, the simulation model are built with PARAMICS. In order to make the difference of simulation results and the actual situation minimal, this paper uses genetic algorithm to calibrate the simulation model.Thirdly, this paper simulates different control strategied. No-control,variable limit speed, on-ramp control and coordinated control are simulated. In order to obtain the optimal scheme, this four control strategies are optimized with genetic algorithm.Finally, this paper analyzes the simulation results. Speed, density, travel time and delay are chosen as indicators to analyze the impact of different traffic control strategies. The results show that variable limit speed can increase travel efficiency of north weaving segment and south-to-north of south weaving segment and coordinated control can increase travel efficiency of middle weaving segment and north-to-south of south weaving segment remarkably.