Simulation Study On The Speed And Capacity Of The Freeway Mixed Traffic Flow

Traffic velocity and capacity are important parameters which reflect the characters of traffic flow. Not only they are the important evaluate index for the capacity analysis and the evaluation of level of service, but also they can supply the visualized decision gist for traffic management. At present the research mostly aims at the simplex vehicle of the free flow in our country, but for the mixed traffic is few. Based on considering the characteristic of the freeway mixed traffic flow, the paper studies the impacts of large and medium vehicles on the traffic speed and capacity of the freeway basic segments, then investigates the relationship between traffic speed and the longitudinal slope, the length of longitudinal slope, volume and the proportion of large and medium vehicles and the relationship between capacity and the longitudinal slope, the proportion of large and medium vehicles as well, which could provide reference to traffic management.The paper reviews the researches on traffic speed and the capacity,and analyzes the characteristics of the freeway mixed traffic, which is that various models of vehicles size is different and vehicle performance is vary greatly. Based on the advantages of traffic simulation in analysis of traffic problems, the paper studies the impacts of large and medium vehicles on the traffic speed and capacity of the freeway basic segments by simulation. After introducing the micro-simulation software TSIS briefly, the paper describes in detail the vehicle generation model, car-following model and lane-changing model of CORSIM. The method of calibration and validation is recommended, and fitness value is used to test the effect. An example is followed in Nan Liu freeway. Then the calibrated model is used to conducts a series of simulation tests in different traffic and road conditionsThrough the processing and analysis of the simulation test date, the author analyzes the relationship between mean speed of mixed traffic flow on the freeway basic segments and four aspects, as the longitudinal slope, the length of longitudinal slope, volume and the proportion of large and medium vehicles. The relationship models are established between traffic speed and the various factors by egression method. In the gentle slope (<3%), the impacts of all factors on traffic speeds is little. In the steep slope (≥3%), with the various factors increasing, the average speed of traffic flow is reduced. And the author studies on the relationship between the actual capacity of the basic segments of freeway and the longitudinal slope and the proportion of large and medium vehicles. The actual capacity models have been established. The paper also gives the recommended values of actual capacity.