三次曲线在超高过渡设计中的应用

线性超高过渡设计采用直线顺坡，在超高过渡段的起、终点都有一个折角，使纵坡发生突变，影响行车的稳定性和舒适性，并导致路面受力发生显著变化．通过对线性超高过渡设计方法缺陷的分析，借鉴理想缓和曲线须满足的条件，提出了超高过渡设计的理想条件，并通过数学推导得出满足理想条件的三次曲线．分析了三次曲线超高过渡可能引起的过渡段附加纵坡过大和横向排水不畅的问题．研究结果表明：采用三次曲线超高过渡，在过渡段长度相同时，附加纵坡最大值为线性过渡的1．5倍，须对超高过渡段最小长度进行重新计算；在超高横坡不大于6％时，横向排水不畅的缓坡路段长度有所缩短，更有利于横向排水．最后，阐述了各种情况下三次曲线超高过渡的设计计算方法．

The application of cubic curve to superelevation transition

The design of superelevation transition with a straight line sloping makes the driving comfort and stability decreased because of the existence of a knuckle in the be- ginning and end of superelevation transition section. By analyzing the defect of tradition- al design methods for superelevation transition, the ideal conditions transition curve was drawn to be fulfilled, and the ideal conditions of superelevation transition design are proposed. A cubic curve which can meet the ideal conditions is derived. The problems that may be caused by cubic curve transition are analyzed. The results show that in the case of the same length of transition section, the maximum of additional longitudinal was 1.5 times than that of the linear transition,so the minimum length of transition section should be recalculated, while superelevation cross slope is not bigger than 6%, the length of poor transverse drainage is shorter, which is useful for horizontal drainage. Fi- nally, various design methods of cubic curve superelevation transition are elaborated.