Driving Speed Decision-Making on Complex Highways Based on Strategy of Trajectory-Speed Coupling

To provide the target speed profile for automatic driving of cars, a speed determination algorithm was presented based on the curvature of pre-view trajectory. Firstly, the position of trajectory on several preview cross-sections was determined and the curvature of each trajectory point was calculated and used as the input data of speed optimization. Secondly, selecting an objective function from minimum traveling time, driving comfort, minimum deviation from the cruise speed and a mixed mode, a speed decision was made under constraints of the lateral/longitudinal driving comfort and the maximum/minimum speed limit using a moving horizon algorithm. With the rolling of preview cross-sections with the forward movement of cars, the desired speed profiles along the distance traveled can be obtained. Finally, a field test was carried out on a complex mountainous highway to validate the proposed model, and examples of trajectory and speed decision of two mountainous highways and an F1 track was illustrated. The results show that: (1) speed profiles of different driving patterns were obtained though the combination of different modes of trajectory control and speed control, which could simulate the various driver behaviors; (2) as the simulated trajectory is generated within the road geometry, factors used for determining the edge of the roadway, such as radius, deflection angle, spirals, pavement width, deflecting direction can all affect the trajectory and then affect the driving speed, therefore the model is applicable to the highways with complex geometrical shapes.