| This paper discusses traffic behaviors on urban expressway. Fistly according to the analysis of spot speed data on urban expressway, the distribution of spot speed is found. Based on the relationship of the relative speed to headway, the influence of the speed disperse towards capacity is found to be objectively in existence. Secondly the statistical models of urban expressway are discussed. Based on summarizing the former analytical methods, the paper presents analytical and disposal methods to data on urban expressway. Using a Cubic equation , we establish a statistical model for traffic flow. Thirdly, this paper confirms the minimal headway for vehicles traveling freely is 6 seconds. Aim at the shortcomings of the former models, the average headway model for various car-following states is put forwards. In this model, the reactive time of drivers is not a constant, but changes along with the speed of vehicles. Through data examination, the model is proved to be strong persuasion towards analysising capacity and traffic behaviors. Finally, through synthesizing the estimated values of urban expressway capacity based on statistic model and average headway model, a suggestion of the possible capacity of basic urban expressway section is recommended.
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