分段式三次抛物线的视距及设计方法

Sight Distance and Design Method of the Transitioned Vertical Curve

竖曲线是纵断面线形设计中的重要组成部分 ,为保证行车安全、舒顺及视距所设置。我国规范规定 :各级公路及城市道路在变坡点处均应设置竖曲线 ,竖曲线形式为二次抛物线。因为在应用范围内 ,圆形与二次抛物线线形几乎没有差别 ,目前国内普遍采用大半径的圆形竖曲线。但由于汽车在圆曲线上行驶时 ,存在着视距不足的缺点。因此 ,本文引进国外新的竖曲线———分段式三次抛物线设计方法[1] ,代替竖曲线中常用的圆曲线 ;并通过太旧高速公路的实例证明分段式三次抛物线的优越性 ,同时提出分段式三次抛物线的设计曲线图 。

The vertical curve pleys a very important role in the design of vertical section designed for traffic safety,comfort and sight distance Under standard specifications, vertical curves should be second?degree parabolas set at the knick points of all levels of highways and urban roads Because there is no difference between circles and second?degree parabolas in the field of application,sweeping circular curves are used generally at the present time However,the sight distance is not enough when cars run in the circular curve Therefore in the paper the new vertical curve?the design method of the transitioned vertical curve is introduced and the method has showed its advantage in Taijiu Highway At the same time the design curve graph of the transitioned vertical curve is proposed which is of practical value for the geometric design.