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从运行角度对长大隧道设计进行专题分析是铁路设计工作中需要重点关注的课题。本文根据线路选线设计中对长大隧道坡度折减普遍套用《铁路线路设计规范》的做法，分析了《铁路线路设计规范》中关于隧道空气附加阻力及坡度系数的条文及条文解释、试验公式；根据设计过程的特点，提出线路设计中，应正确理解、灵活使用设计规范，指出相关参数的取值应结合具体铁路项目的地形、地质条件和技术标准，兼顾工程投资和运营条件来确定，重点讨论了在长大隧道内线路坡度折减系数的合理确定。最后，本文就长大隧道坡度折减系数的分析及标准本身的研究提出了建议。

On Gradient Reduced Coefficient of Traction in Long Tunnels

Studying the long tunnel geometric design from its actual operation is the issue should be paid close attention in railway design. Currently, the common approach to determining gradient reduction coefficient of traction is from the Code for Design of Railway Line. This paper analyzes the provisions and experimental expressions about additional aerodynamic drag in tunnel and gradient coefficient in the Code. It emphasizes correct comprehension and flexible application of the Code. The parameter value should be calculated considering the topography, geological conditions, technical standard, investment, and operating conditions of the railway project. The paper concentrates on how to determine the gradient reduced coefficient of traction in long tunnels properly. It also gives some suggestions on the studies of gradient reduced coefficient of traction in long tunnels and the design standard.