The National Academies

NCHRP 22-22(02) [Final]

Effectiveness of Traffic Barriers on Non-Level Terrain

  Project Data
Funds: $420,742
Research Agency: Texas A&M Research Foundation
Principal Investigator: Roger Bligh
Effective Date: 6/12/2012
Completion Date: 12/11/2015

The objective of this project was to produce comprehensive recommendations for placement of barriers on roadside and median slopes. The guidelines address all of the common types of barriers used in the United States.

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 did not include barrier terminals.

The Agency's final report includes: (1) description of the research effort to develop the placement guidelines and (2) the placement guidelines. It is available to download at the link below: https://onlinepubs.trb.org/Onlinepubs/nchrp/docs/NCHRP22-20(02)FinalReport.pdf

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