# Three-Dimensional Stopping Sight Distance Calculation Method under High Slope Restraint
## 1 Introduction
analyzed the effects of 3D flat and vertical curve combinations on driver psychology and sight distance perception. The results show that the driver's curve perception depends on the slope change [14]. In another article, [PERSON] et al. developed a finite element-based application using Matlab, calculated the sight distance value for the overlap of the flat and vertical curves, and pointed out that the S.S.D. depends mainly on the ratio of convex vertical curve parameter to the horizontal radius, but the study did not verify the actual road [15]. [PERSON] et al. calculated and evaluated the road section limited by the overpass structure by establishing a three-dimensional virtual road model, and |applied it to the sight distance analysis of a road underpass, but the modeling and assumptions of the road are relatively simple, making the final calculations less accurate [16]. [PERSON] et al. applied reliability analysis to evaluate the sight distance occlusion of left-turn vehicles at intersections, but the model only analyzed the driver's visual conditions from the plane and ignored the effects of slope and roadside obstacles [17]. [PERSON] et al. proposed a new sight distance calculation model based on GPS data, and verified the actual road section in Sri Lanka. However, the model is still calculated based on the planar two-dimensional sight distance and the reliability on the longitudinal slope section needs to be analyzed [18]. [PERSON] et al. established a sight distance calculation model based on support vector machine, and applied the model to the sight distance test of the actual tunnel, but the prediction accuracy of the model needs to be further improved [19]. [PERSON] analyzed the S.S.D. of the outer lane of the central separation zone according to the driving characteristics of the car in the overtaking lane. However, it was evaluated by the method of horizontal sightline offset (H.S.O. ), and the S.S.D. value could not be obtained intuitively [20]. [PERSON] et al. established a dynamic S.S.D. calculation model by analyzing the vehicle position, driver's viewpoint position,vehicle width, road cross-sectional width, and radius of the curve during actual driving, but the model is still a two-dimensional calculation model and can not accurately describe the actual driving state [21]. Summarizing the above papers, we can know that the main analysis methods of 3D sight distance include two-dimensional sight distance calculation optimization model, graphic simulation, and mathematical analysis method. The sight distance calculation optimization model does not take into account the spatial characteristics of the road alignment; the graphical simulation method requires the establishment of a real three-dimensional road environment, which requires a lot of work, high cost, and long cycle, and cannot realize the rapid detection of the road sight distance, which is not conducive to popularization. In this paper, through the analysis of poor sight distance caused by high slope occlusion when the car is turning right, using the actual design data of the road, a three-dimensional parking line-of-sight calculation method based on horizontal and vertical combination is established. Finally, the S.S.D. calculation of the actual secondary highway from different angles of design speed and operating speed is carried out. The results show that the proposed method has the advantages of being intuitive and accurate.