Research on Theoretical Calculation Method of Composite Gradient Threshold for Highways

To address the issue of the lack of a definitive theoretical calculation method for composite gradients, this study systematically analyzes the dynamic characteristics of vehicles, such as climbing performance, anti - landslide performance, braking performance, and lateral stability performance, when driving on composite gradient sections, based on the spatial relationships of composite slope angles, lines, and planes. By deriving and establishing calculation formulas for the dynamic performance of vehicles driving on composite gradients, deeply analyzing the influence laws of composite gradients on various dynamic performances, and combining with the method for determining the extreme values of constraint conditions, the threshold range of composite gradients under the design parameters of extreme road alignments is finally obtained, and the theoretical calculation method for the threshold of composite gradients is determined. The research results show that the setting of the minimum value of the composite gradient needs to ensure the lateral drainage capacity of the road, and the determination of the maximum value should aim to ensure the driving comfort; on snow - and ice - covered sections, the composite gradient should be determined according to local conditions and actual situations. The conclusions of this study can provide a theoretical reference for the revision of highway alignment design specifications and the design of composite gradients.