Single-vehicle accident modelling method on freeway

The collected single-vehicle accidents were analyzed by using random trial and mathematic equalization principle. The area function of single-vehicle accident rate was computed by definite integral element method. The affecting factors and geometric variables of traffic accident were selected one by one according to the change rule of area function, the affecting model of every variable was set up, and the final variables were determined. The single-vehicle accident forecast models were established in the sections with different radiuses and linear lengths by using regression analysis. The suitable curve radius and linear length were proposed through analyzing the 3D surface charts of the models. Research result indicates that in freeway design, the reasonable radius of a curve is in the interval [2500, 3500], and a linear length is in the interval [1000, 2000] for the alignment combination of straight line-curve-straight line. When the radius of curve is more than the minimum radius without superelevation, it is 1000 for the linear length of that is connected with the curve.