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Recommended Guidelines for the Selection and Placement of Test Levels 2 through 5 Median Barriers

项目名称：	Recommended Guidelines for the Selection and Placement of Test Levels 2 through 5 Median Barriers
摘要：	Median barriers can be divided into six test levels, as defined by the 2009 AASHTO Manual for Assessing Safety Hardware (MASH) and NCHRP Report 350, which represent the types of vehicles the barrier is designed to redirect. A test level is defined by impact conditions (speed and angle of approach) and the type of test vehicle (ranging in size from a small car to a fully loaded tractor-trailer truck). The longitudinal barrier is the only classification for which all six test levels are defined at this time. Longitudinal median barriers are also grouped into three general categories: flexible, semi-rigid, and rigid. Although a rigid barrier and a flexible barrier can be designed to satisfy a given test level, they will have different applications. The rigid barrier will produce higher vehicle decelerations and prevent any lateral deflection while the flexible barrier will produce lower accelerations. Less rigid barriers result in less energy dissipated by the vehicle; hence, accelerations imparted to the occupants inside the vehicle during an impact are lower as compared to vehicle impacts with rigid barriers. On the other hand, flexible barriers have been shown to have larger lateral deflections, thus limiting their use in narrow medians. The crash test procedures for median barriers have seen much progress over the years, as evident by the publication of NCHRP Report 230, NCHRP Report 350, and most recently, the MASH. Currently, the AASHTO Roadside Design Guide (RDG) is the primary national guideline available to states in preparing their own policies for roadside design. The RDG offers guidance for the selection of median barriers, citing a higher percentage of heavy trucks in the traffic flow, adverse geometries, and higher accident rates as conditions that may warrant barriers with a performance level higher than Test Level 3. However, thresholds for these values are not provided. Additional guidance on the selection and placement of median barriers would complement recently developed guidance for bridge rails and would help better define these thresholds while helping to balance public funds with improved safety. The objective of this research is to develop, in a format suitable for consideration and possible adoption by AASHTO, proposed guidelines for the selection and placement of Test Levels 2 through 5 median barriers. The guidelines should be based on traffic volumes and characteristics, roadway and median geometry, median barrier placement, in-service performance, cost benefit, risk analysis, and barrier type (i.e., shape, material, rigidity, etc.). The guidelines will also include charts with associated site-specific adjustment factors for the selection of the appropriate median barrier test level and for use in the selection of median barrier type and placement within the median. The guidelines should be suitable for use by all government transportation agencies at the state and local level. It is anticipated that the results will be integrated into an updated edition of the AASHTO Roadside Design Guide (RDG).
状态：	Active
资金：	300000
资助组织：	National Cooperative Highway Research Program
项目负责人：	Jared, David
执行机构：	Roadsafe LLC
主要研究人员：	Carrigan, Christine E
开始时间：	20150928
预计完成日期：	20200530
实际结束时间：	0