In the 1970s, an analysis of barriers placed on slopes indicated that most guardrails do not perform well when placed on 1:6 or steeper slopes. Since that time, the vehicle fleet has changed dramatically, with the popularity of light trucks and sport utility vehicles increasing dramatically. Further, there has been a significant change in the design of roadside barriers in recent decades. High-tension cable barriers are beginning to gain widespread acceptance, and there have been changes to the traditional W-beam barriers. It is unclear how these changes affect the behavior of longitudinal barriers placed on slopes.
Information from the NHTSA FARS database indicates that some cross-median crashes have occurred where median barriers were in place. Further, a full-scale crash test has shown that a passenger vehicle can penetrate a cable barrier on the back-slope of a depressed median. With the dramatic increase in use of barriers in depressed medians, a more detailed study of the performance of barriers in depressed medians is needed to achieve acceptable safety performance. The scope of this study does not include barrier terminals.
The objective of this project was to produce comprehensive recommendations for placement of barriers on roadside and median slopes. The guidelines should address all of the common types of barriers used in the United States.
The work is being completed in NCHRP Project 22-22(02).
TASKS (1.) Define representative scenarios of combinations of slope configuration and soil type. Describe the common types of barriers used in the United States. (2.) Develop a detailed simulation modeling plan and refine the preliminary crash testing plan included in the proposal. The plans must meet NCHRP Report 350 requirements (as amended) and must include situations where the barrier is on the back-slope of a depressed median. (3.) Within 4 months of the contract start, submit an interim report summarizing Tasks 1 and 2. The NCHRP 22-22 contractor will be expected to meet with the NCHRP and the principal investigator for NCHRP Project 22-21 approximately 1 month later. It is expected that the meeting will be at the contractor's (or subcontractor's) facilities and will include a demonstration of the simulation-modeling capabilities and the crash-testing facilities. The contractor shall not begin work on the remaining tasks without NCHRP approval. (4.) Conduct simulation modeling in accordance with the approved plan. Refine the plan for crash testing. Submit a technical memorandum detailing the results of the simulation modeling and including the refined crash testing plan. Work may proceed while this memorandum is reviewed by NCHRP. (5.) Conduct crash testing in accordance with the refined plan to verify the results of the simulation modeling. (6.) Submit a final report that describes the research effort and includes placement guidelines for common types of roadside and median barriers on slopes to provide adequate safety performance for impacting vehicles. The report should include specific recommended changes to the AASHTO Roadside Design Guide. Video of the simulation modeling and crash tests should be included on a CD-ROM or DVD.