A road weight evaluation method based on grey neural network was proposed.The advantages of grey forecasting model,which is simple and needs less original data,and neural network were synthesized to establish the grey neural network model of traffic flow.The relationships between traffic flow,velocity and density were used to determine the relational model of flow and time.On these bases,the impedance function model and the weight of road sections were achieved.The experiment results show that the model has higher accuracy and only a few measurement data are needed to confirm the impedance function model of road sections.The model is an effective,feasible and convenient method for getting the weight of road sections.It can be applied in the road planning of intelligent transportation system.