中文摘要：

长大下坡路段是重型载货车多发事故区域。当前针对重型载货车发生事故的研究大都集中在车辆超速方面,忽略了车型、天气、驾驶人特性等因素。本文通过分析云南罗富高速公路某长大下坡路段在2012年内的重型载货车事故数据,研究车型、天气、驾驶人特性等因素对重型载货车事故的影响。统计分析了不同因素影响下重型货车在长大下坡路段发生事故数的分布规律;然后利用K均值聚类算法,依据不同因素造成的事故严重程度（事故量、受伤人数、死亡人数）,将所有的因素分为3类。研究结果显示,外地车辆、六轴车和在00：00—07：59时段发生交通事故的严重程度最重,而有雾、有雨和低温对事故的影响很小。

英文摘要：

Long downgrade road sections are dangerous parts for heavy-duty truck accidents. Most of current researches on heavy-duty truck accidents are focused on the speeding of truck, which ignore other factors（weather, vehicle types, driver attribute, etc.）. Through analysis of accident data in long downgrade sections of Luofu Freeway in Yunnan Province, the effects of weather, vehicle types, driver attribute, etc. on heavy-duty truck accidents are studied in this paper. First, descriptive statistical analysis method is used to study the accident distribution of different factors. Then using K-mean clustering method, the factors are divided into three clusters based on their effects on accident severity（accident number, occupant injuries, and deaths）. The study results show that non-local trucks, 6-axle trucks and 00∶00-07∶59 are the most important factors on accident severity in long downgrade road sections; fog, rain and low temperature have little effects on accidents in long downgrade road sections. The study results may be used as a reference basis to improve heavy-duty truck transportation safety in long downgrade road sections.