中文摘要：

道路水平排列包含三个元素：直线，圆形的弧，和 clothoid。在 Autocad， clothoid 能被多线或花键仅仅适合，并且与道路数据被分开的图形独立于对方。因此，为道路开发新弯曲是必要的水平排列。第一，为 clothoid 的微分近似和系列集成方法被讨论。第二，为包含三个元素的道路线的几何公式总体上被导出。然后，设定一个道路线类的优点和可行性，从弯曲基类被导出，基于 ObjectARX (Autocad 运行时刻扩展) 被分析技术。最后，为道路线班的数据结构和操作被强调。试验性的结果证明道路线能集成实现面向图形的设计的道路元素，图形和数据，它能广泛地在道路排列设计被使用。

英文摘要：

Road horizontal alignment contains three elements： straight line, circular arc, and clothoid. In AutoCAD, clothoid can only be fitted by polyline or spline, and the graphics which are separated from the road data are independent of each other. Therefore, it is necessary to develop a new curve for road horizontal alignment. Firstly, the differential approximation and series integration methods for clothoid were discussed. Secondly, the geometric formulae for road line which contain the three elements were derived as a whole Then, the advantages and feasibility of customizing a road line class, which was derived from the curve base class, were analyzed based on ObjectARX （AutoCAD Runtime eXtension） techniques. Finally, the data structure and operations for the road line class were stressed. The experimental results show that the road line can integrate the road elements, graphics and data to implement the graphics-oriented design, which can be widely used in road alignment design.