Abstract: long and steep downhill mountain roads are usually the hazardous locations，especially for the overload and fast going heavy-duty vehicles which are more likely to occur to the trafic accidents．So the relationship between longitudinal gradi- ent，grade length limit，vertical cLlrve an d safety is analyzed，which can be referred to improve the safety and optimize the profile design．

Key words: longitudinal gradient, grade length limit, vertical curve, operating speed

摘要： 山区长大下坡路段往往是事故多发路段，尤其是重型载重车辆的超载快速行驶更易引发重大、恶性交通事故． 根据下坡路段事故统计资料，分析纵坡坡度、坡长、竖曲线和下坡衔接平曲线与道路安全的关系，为提高长大下坡路 段安全，优化纵面设计提供参考．

关键词: 纵坡, 坡长限制, 竖曲线, 运行速度