Abstract: Highway geometric design is an important part of highway construction,which directly influences the safety and comfort of driving.In order to overcome the shortcomings of the separated horizontal and vertical alignment design methods,by adopting the curvature and the torsion as new alignment design indexes,a new method for the three-dimensional highway geometric design is developed based on the fact that the highway centerline is a three-dimensional curve in nature.Then,by analyzing the engineering constrains of the three-dimensional highway alignment design from the aspects of geometric continuity,vehicle stability and driving comfort,a constraint model is constructed.Finally,the design values of the three-dimensional alignment indexes at different design speeds are determined based on the current design guidelines and experiences and by integrating the constructed constraint model.This new design method can avoid the limitations of unmeasurable combined effects and geometric continuity degradation in the traditional design method,and it provides a new solution to improving the safety of highway alignment design.

Key words: road engineering, three-dimensional alignment design, curvature, torsion, geometric continuity, vehicle stability, driving comfort