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横断面要素指标是双车道公路的重要控制指标，上述指标的选择对于双车道公路的安全性和通行能力有很大影响，在山区尤为明显. 本文根据24条山区双车道公路的现场勘察结果和交通事故、交通组成等数据，对山区双车道公路横断面要素的安全性进行了分析研究. 研究内容包括路基宽度、车道宽度和路肩宽度指标对全部事故和不同形态事故的影响规律，并借用负二项分布模型针对路基宽度指标进行了事故预测研究. 研究结果表明，路基宽度和路肩宽度对于全部事故和各类别事故的影响整体上皆为先增加后降低的趋势；构建的追尾事故预测模型中货车比例、接入口、路基宽度的二次式几个因素将增加追尾事故，而路基宽度的增加有利于降低追尾事故.

Safety of Cross-Section on Two-Lane Highways in Mountainous Areas

The width of subgrade and shoulder has strong relationship with the safety and capacity of two-lane highways in mountainous areas. On the basis of the survey data collected from 24 two-lane highways in mountainous areas, the paper explores the relevant safety factors in this kind of area. It analyzes the relationships of all accidents, injury accidents, rear accidents, roadside accidents and collision accidents with the factors of subgrade and shoulder. Negative Binomial regressions are applied to fit the total crashes with subgrade width, truck proportion, and other factors. The results indicate that all kinds of accidents increase first and decrease then with the increases of subgrade and shoulder width. In the rear-end prediction model, several factors like the propitiation of truck and entrances lead to more rear-end crashes, and the increase of subgrade width reduce the probabilities of rear-end crashes.