International crash data indicate that roadside characteristics contribute to more than half of all roadside accidents involving serious injury or death. Therefore, research on roadside safety is urgently needed. Based on the vehicle departure speed, pavement height (i.e., the difference between pavement elevation and ground elevation), slope gradient, and horizontal curve radius, this study uses PC-Crash simulation software to carry out tests of trucks and cars exiting a road. A chi-squared automatic interaction detection (CHAID) decision tree is used to explore the causative mechanism of vehicle rollover, and the concept of a “safe slope” to ensure that vehicles do not roll over is proposed. Aiming at straight and curved sections, discriminant functions of vehicle rollover and nonrollover are fitted through Bayesian discriminant analysis, and safe slope calculation models for trucks and cars are then constructed. Based on the obtained safe slope models, calculation methods for the safe slope and the roadside clear zone width involving different traffic compositions are proposed by calibrating the lateral distance from the final position of nonrollover vehicles to the road edge. The results show that the factors affecting vehicle rollover are, in descending order of importance, the slope gradient, pavement height, vehicle type, departure speed, and horizontal curve radius. For a section with a large proportion of cars, the slope gradient should not be steeper than 1:3.5. The horizontal curve radius should not be less than 600 m for a section with a large proportion of trucks and a slope gradient steeper than 1:3.5 or shallower than 1:2.5. Additionally, for a section with a pavement higher than 0.5 m and a slope gradient steeper than 1:2.5, the operating speed limit should be lower than 60 km/h. These research results have theoretical value and practical significance to improve the driving safety level and reducing the risk of roadside accidents.

中文翻译：

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基于安全坡度的公路沿线净带宽度计算

国际碰撞数据表明，在所有涉及严重伤害或死亡的路边事故中，有一半以上是由路边特征造成的。因此，迫切需要对道路安全进行研究。本研究根据车辆离开速度、路面高度（即路面标高与地面标高的差值）、坡度和水平曲线半径，利用PC-Crash仿真软件对出路的卡车和汽车进行测试。使用卡方自动交互检测（CHAID）决策树探索车辆侧翻的原因机制，并提出了“安全坡度”的概念，以确保车辆不会侧翻。针对直线段和曲线段，通过贝叶斯判别分析拟合车辆侧翻和非侧翻的判别函数，然后构建卡车和汽车的安全坡度计算模型。基于获得的安全坡模型，通过标定非翻车车辆最终位置到道路边缘的横向距离，提出了涉及不同交通构成的安全坡和路侧净区宽度的计算方法。结果表明，影响车辆侧翻的因素按重要性从高到低依次为坡度坡度、路面高度、车辆类型、出发速度和水平弯道半径。对于汽车比例较大的路段，坡度不应大于1:3.5。货车比例较大，坡度大于1：3.5或小于1：2.5的路段，水平曲线半径不应小于600m。此外，路面高度大于0.5m，坡度大于1:2.5的路段，限速应低于60km/h。这些研究成果对提高行车安全水平、降低路边事故风险具有理论价值和现实意义。