山区公路测量时,有时因控制点间的高差过大,靠自然展线无法满足纵坡的要求时,或因地形、地质条件的限制采用自然展线致使工程过于艰巨或质量难以保证时,路线则可利用相宜的地形设置回头曲线进行展线。不管在什么情况下设置回头曲线都必须符合路线纵坡标准时才能成立。由于回头曲线半径小,线型标准低,行车条件差,除非 In mountainous area, when the height difference between control points is too large and the natural slope can not meet the requirement of longitudinal slope sometimes, or when the natural stretch line is limited by the topography and geological conditions, making the project too difficult or the quality is hard to be guaranteed, The route can use the appropriate terrain set back curve for exhibition line. No matter in what circumstances to set the back curve must meet the criteria for longitudinal alignment can be established. As the back curve radius is small, low standard linear, poor driving conditions, unless