Research On The Traffic Flow Theory And Its Application On The Freeways

Intelligent Transportation System (ITS) assembles advanced information technology, communication technology, control technology, sensor technology, and system integration technology efficiently, and applies them to the ground transportation system. ITS constructs an effective in large-scale, real time, exact, and efficient transportation system. In the research of ITS, traffic flow theory is one of the basic.Traffic flow theory is a frontier and developing science that seeks to describe the characteristic of traffic in mathematical and physical way. At present, there isn't an integrated theoretical system. In the research of highway capacity, the development and perfection of traffic flow theory has incarnated the deepness and width in research. Capacity research is limited to experiential or semi-experiential method so far because of the complexity of traffic behavior. Each country has respective method that isn't prevalent. There isn't a set of accepted theoretical system.In this paper, we study traffic flow from the viewpoint of hydrodynamics, and set up the traffic flow theory that can be used to calculate the highway capacity and judge the level of service. The research and contribution in detail are introduced as follow:(1) The driver characteristics > motor vehicle characteristics , road characteristics, macroscopic and microscopic flow parameters are analyzed. A new traffic flow continuum hypothesis is proposed. The compression index and elasticity coefficient are defined. Compression indexes for some speed-density are calculated.(2) The Eulerian description is expounded in researching traffic flow. Conservation of mass, second Newton's law, and momentum law are introduced into traffic flow to set up traffic continuity equation, Euler's equation, and momentum integral equation. The relative viscosity hypothesis is put forward andintroduced in Euler's equation to establish viscosity momentum differential equation. The speed-density constant model and Greenshields' speed-density linear model are adopted to verify the hypothesis.(3) Relationships among traffic flow parameters suitable for ITS are obtained. Comparing with the traditional models, relationships include free flow density, and coincide with the field data observed on freeways.(4) According to the coefficient in momentum differential equation, some traffic flow models are classified, analyzed and predicted by means of characteristic curve method.(5) As to the numerical experiments, three cases are chose to testify the applicability of the model in the paper. The numerical cases show that the model can reasonably describe the nature of traffic flow. In numerical simulations, the maximum wave velocity is the only identification parameter. With the traditional models, the model in the paper is more convenient.(6) A highway capacity calculating model for basic sections is set up by using the maximum wave velocity. Actual capacities of Guangzhou-Shenzhen, Guangzhou-Foshan and Shanghai-Nanjing freeway are calculated. Using the data from Highway Capacity Manual 2000, the capacities under the different weather are predicted. Identifying the maximum wave velocity, the actual capacity can be calculated. The maximum wave velocity can be determined upon the data in low density. So, even if having the data in low density, the actual capacity can be calculated correctly.(7) By non-dimensional traffic pressure, an evaluating index system for level of service of highway is set up. According to the statistical data, the LOS' of 'static state' of Guangzhou-Shenzhen and Guangzhou-Foshan freeway are evaluated. According to the 5min data, the LOS' of 'real-time state' of Guangzhou-Foshan and Shanghai-Nanjing freeway are evaluated. The index system is a uniform and coherent index system of grading service for different highways, and suitable for the purpose of high speed and large flow of ITS.