山区公路回头曲线小客车纵向行驶特性及运行速度模型

Longitudinal driving characteristics and operating speed prediction model of cars on hairpin curves of mountainous roads

为明确山区公路回头曲线路段小客车的纵向驾驶行为特性,以国道G211线重庆市彭水县花地湾至宁家寨段为试验道路,开展了小客车实车驾驶试验。采集了自然驾驶状态下的车辆轨迹、速度、加速度等数据,分析了回头曲线路段的速度幅值特征;明确了上坡和下坡方向的速度行为模式,得到了速度变化特征点位置的分布规律;研究了入弯减速度和出弯加速度的幅值特征和影响因素。结果表明:回头曲线路段的车辆行驶速度明显高于道路设计速度和限速值,超速行为非常普遍;上坡方向为“减速-加速”两阶段速度模式,与一般弯道存在差异;下坡方向为“减速-匀速-加速”三阶段速度模式;速度特征点分布位置受到视距、坡度和曲线偏角等因素的影响,且与常规假设存在一定差异;上坡回头曲线的速度谷值点位置主要分布于圆曲线前半段;下坡方向减速止点主要集中在缓和曲线-圆曲线连接点与圆曲线中点附近,加速起点主要分布于圆曲线和第二缓和曲线范围内;回头曲线下坡方向和上坡方向的入弯减速度85分位值分别为1.25和1.0 m/s^(2),下坡方向和上坡方向的出弯加速度85分位值分别为0.9和0.6 m/s^(2),即坡向和坡度对加(减)速度存在显著影响。最后,建立了回头曲线路段入弯、弯中和出弯阶段的运行速度模型,并进行了验证。本文研究成果可为艰险山区复杂线形公路的安全性评价以及安全改善提供理论支撑和基础数据支持。

To clarify passenger cars'longitudinal driving behavior along hairpin curves of mountain roads,the section from Huadiwan to Ningjiazhai of national highway G211 located in Pengshui County,Chongqing,China was selected as the object.The field driving test of passenger cars was carried out to collect trajectory,speed,and acceleration data.Firstly,the characteristics of speed amplitude were analyzed,and the vehicle speed modes in the direction of uphill and downhill were defined.Then,the distribution law of the speed change feature points'position was obtained.Finally,the deceleration and acceleration's amplitude characteristics and influencing factors are studied.The results show that in the curved section,the actual speed is significantly higher than the design speed and speed limit,and the overspeed behavior is very common.The speed pattern of hairpin curves along uphill direction is a‘decelerate-accelerate’two-stage speed mode,different from the speed pattern of a standard horizontal curve.The speed pattern for hairpin curves in downhill direction presents three-stage of‘decelerationconstant speed-acceleration’.The position of speed feature points is affected by sight distance,slope,and deflection angle,which is different from the conventional driving behavior assumption.The speed valley points of the uphill are mainly distributed in the first half of the circular curve.Deceleration endpoints in the downhill direction appear near the SC and MC points;and the acceleration starting point is mainly distributed in the circular curve and the second spiral range.The 85 percentile deceleration rate when entering a hairpin curve on the downhill is 1.25 m/s^(2),and the one on the uphill is 1.0 m/s^(2).When departing the hairpin curve,the 85th percentile acceleration rate is 0.9 and 0.6 m/s^(2),respectively,for downhill/uphill curves.Finally,an operating speed model for entering,departing,and staying in the hairpin curves was developed and verify.The research results can provide theoretical and basic data support for the safety evaluation and improvement of complex roads in dangerous mountainous areas.