既有线提速以适应铁路走向市场的需要己成为共识。在既有线提速的勘测设计，应注意区别“达速”与“提速”的概念。达速与提速的最终目标是提高旅行速度，缩短旅行时间。为提高旅行速度要采取综合措施，并注意处理工程投入与获取效益间的关系，注意处理近期实施与长远规划的关系，注意处理土建工程改造与移动设备更新的关系，注意处理客车提速与货车提速的关系。

Raising speed on existing railway lines to meet the needs of railways facing on the market has become a common programme. During the survey and design for raising speed on existing railway lines，the conceptions of "up to speed" and "raising speed" should be taken into attention to distinguish. The final targets of them are to increase the travelling speed and to reduce the travelling time. In order to increase the travelling speed，the comprehensive measures should be adopted and the treatment of follwing relations should be taken into attention，such as the relation between investment and benefit of engineering project，between short-term installation and long-term planning between reconstruction of civil engineering and renewal of portable equipment，between raising speed of passenger trains and freight trains，etc.