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针对城市道路路段上车流的流量和密度之间的特性，对道路元胞自动机交通流模型进行了改进，使CA模型能够较好模拟城市道路交通流。提出了网格动态调整算法，该算法根据模型模拟的路段流量和密度计算车辆平均通行距离，并以此距离动态调整CA模型的格子长度，按照城市道路路段上车辆速度的统计分布规律，以路段的车流速度密度模型输出作为下步模拟的平均车速，通过车辆速度的分布范围确定车辆加速减速的概率，对模型车速进行更新。选择500米长的城市主干道上的一条车道，利用本文改进的CA模型进行模拟，模拟结果表明:该模型在车速为30-65公里/小时范围内，能较好模拟城市道路上车流的运行特性。改进后的CA模型，适用于对城市道路上中速车流运行状况的模拟。

Cellular Automata Model of Urban Road Traffic Flow Based on Characteristic of Traffic Density and Speed

Based on the characteristic of the traffic flow on urban road, an improved CA tragic model is proposed. The improved model can simulate urban road traffic flow preferable. The paper introduces the dynamic lattice arithmetic which adjusts the lattice length of CA model according to the average vehicles passing distance. Speed is update in term of the statistical rule of the urban road traffic speed which is gained through the road urban traffic volume density model and the road tragic speed statistical rule. A lane of an urban trunk road of 500 meter is chosen to simulate the traffic flow with the improved CA model. Simulating result indicates that the improved CA traffic model has preferably effect when the speed between 30 to 65 Km/h. The improved CA model can be used for simulating the urban road traffic flow of median speed.