New design method for horizontal alignment of complex mountain highways based on “trajectory–speed” collaborative decision

Abstract

The safety evaluation of geometry features design based on actual driving behavior has always been a basic concept of highway design. However, current design methods, including both the design speed method and operating speed method, are still far away from real-world driving conditions. In this work, we propose a new alignment design method which can take into account typical handing patterns (driving styles) of human drivers and can pay special attention to dangerous driving behaviors. The core of the proposed method is forecasting the trajectories of typical direction control patterns within roadway width, which can be used by drivers. Then, forecast the driving speed of typical speed control patterns on the basis of the curvature of the preview trajectory just determined. Mathematical programming method was used in this study, whereby the objective functions and constraints were developed to model the typical driving patterns. This article provided five direction control patterns and four speed control patterns to designers so that they could select an appropriate pattern to predict the trajectory and speed for the designed road. Finally, the trajectory and speed are used to control the geometric features of the road. Geometric features can determine the driveway shape, such as curve radius, deflection angle, spiral length, tangent length, roadway/lane/shoulder width, and any or all of these can be adjusted by the designer. Meanwhile, as more than one driving pattern is optional and vehicle performance, driving stability, and ride comfort restrictions are introduced to trajectory/speed decision-making, the new method more closely approximates to real-world driving than conventional methods. The application example shows that the proposed method is especially suitable for the horizontal alignment design of low/medium design speed highways that traverse rugged terrain.