Virginia Tech, Department of Biomedical Engineering and Mechanics, 445 Kelly Hall, Stanger St. (MC 0194), Blacksburg, VA 24061-0194, United States.
Chalmers University of Technology, 41296 Göteborg, Sweden.
Accid Anal Prev. 2015 Jul;80:162-71. doi: 10.1016/j.aap.2015.03.020. Epub 2015 May 20.
The 2011 AASHTO Roadside Design Guide (RDG) contains perhaps the most widely used procedure for choosing an appropriate length of need (LON) for roadside barriers. However, this procedure has several limitations. The procedure uses a highly simplified model of vehicle departure, and the procedure does not allow designers to specify an explicit level of protection. A new procedure for choosing LON that addresses these limitations is presented in this paper. This new procedure is based on recent, real-world road departure trajectories and uses this departure data in a more realistic way. The new procedure also allows LON to be specified for a precisely known level of protection - a level which can be based on number of crashes, injury outcomes or even estimated crash cost - while still remaining straightforward and quick to use like the 2011 RDG procedure. In this analysis, the improved procedure was used to explore the effects of the RDG procedure's assumptions. LON recommendations given by the 2011 RDG procedure were compared with recommendations given by this improved procedure. For 55 mph roads, the 2011 RDG procedure appears to lead to a LON sufficient to intercept between 80% and 90% of right-side departures that would otherwise strike a hazard located 10 m from the roadway. For hazards closer than 10 m, the 2011 RDG procedure intercepts progressively higher percentages of real-world departures. This suggests the protection level provided by the 2011 RDG procedure varies with the hazard offset, becoming more conservative as the hazard moves closer to the roadway. The improved procedure, by comparison, gives a consistent protection level regardless of hazard location.
2011 年美国 AASHTO 路边设计指南（RDG）可能包含了选择路边护栏合适长度（LON）最广泛使用的程序。然而，该程序有几个限制。该程序使用了高度简化的车辆偏离模型，并且该程序不允许设计者指定明确的保护水平。本文提出了一种新的选择 LON 的程序，以解决这些限制。这个新程序是基于最近的、真实世界的道路偏离轨迹，并且以更现实的方式使用这些偏离数据。新程序还允许为确切已知的保护水平指定 LON——该水平可以基于碰撞次数、伤害结果，甚至估计的碰撞成本，同时仍然像 2011 年 RDG 程序一样简单快捷。在这种分析中，改进后的程序用于探索 RDG 程序假设的影响。2011 年 RDG 程序给出的 LON 建议与改进后的程序给出的建议进行了比较。对于 55 英里/小时的道路，2011 年 RDG 程序似乎导致了足够长的 LON，可以拦截 80%到 90%的否则会撞击到距离车道 10 米处的障碍物的右侧偏离。对于距离小于 10 米的障碍物，2011 年 RDG 程序会拦截越来越多的现实偏离。这表明 2011 年 RDG 程序提供的保护水平随障碍物偏移而变化，随着障碍物靠近车道，保护水平变得更加保守。相比之下，改进后的程序无论障碍物位置如何，都提供了一致的保护水平。
