Abstract: A general model structure is proposed to describe urban traffic flow in order to study the dynamic characteristics of the traffic flow.Some typical dynamic units are presented to describe the traffic flow of an intersection，which are the representation of the road network traffic flow.The study is carried out by means of simulation experiments.In order to get the input/output data of the simulated traffic flow under different conditions，many different simulation experiments are designed.Using the input/output data，the transfer functions model of the traffic flow at intersection is put forward based on the methods of system identification.The research shows that the transfer functions of the cycle control channels are three-order systems；the transfer functions of the split control channels are two-order systems.The transfer functions model can describe the states of traffic flow of an intersection，and it can be used to study the dynamic characteristics of the traffic flow.

Key words: urban traffic control, transfer functions model, system identification, intersection

摘要： 为研究交通流对象动态特性，提出了描述城市交通流对象的一般模型结构，确定了描述单路口交通流为代表的城市路网交通流的典型动态环节。通过设计不同的仿真试验内容，获得了不同条件下的不同仿真交通流的输入输出数据，基于系统辨识的方法分别建立了单路口交通流的传递函数模型。研究表明，城市交通流的周期控制通道传递函数为三阶系统；绿信比控制通道传递函数为二阶系统。该传递函数模型能够很好地描述交通流状态，可以用于交通流对象动态特性研究。

关键词: 城市交通控制, 传递函数模型, 系统辨识, 交叉路口