In the design and installation of guardrail systems, there routinely exists a need to provide a stiffening mechanism to locally reduce the lateral deflection distance where there is an area of concern such as bridge piers, poles, and other rigid objects located near roadway shoulders. Various means of providing reduced deflections have been made with past systems that have included nesting of guardrail and the reduction of guardrail post spacing. With the adoption of the American Association of State Highway and Transportation Officials (AASHTO) 2016 Manual for Assessing Safety Hardware (MASH), there is currently little to no guidance on the use of deflection limiting techniques for MASH compliant guardrail installations and their necessary transitions. Thus, a need exists to provide guidance for the use of stiffening mechanisms that will reduce the deflection distances behind guardrail while maintaining the integrity and safety performance. This research will continue the development of guidance for the design and installation of reduced deflection guardrail systems that are MASH compliant.
Most research on guardrail used the NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features testing criteria. The AASHTO and Federal Highway Administration’s (FHWA) Joint Agreement for the Implementation of MASH requires the use of MASH compliant hardware. Further research is needed and should be conducted using the most commonly used 31 in. generic guardrail system, the Midwest Guardrail System (MGS).
The objective of this research is to develop guidance for the practical and cost effective use of stiffening mechanisms to locally reduce the deflection for MASH TL-3 compliant 31-in. MGS installations or equivalent guardrail including any needed transition from the standard system to the stiffened system while maintaining its integrity and safety performance.
The guidelines are to consider the effects of dynamic deflections and working width, fill condition behind the system, post spacing, post length and embedment depth, nested rail, block-out depth, barrier offset, and full development length of the stiffening mechanism. It is anticipated that a combination of previous research, computer simulation modeling, and full-scale crash testing conducted by an ISO 17025 certified crash laboratory will be required to develop and verify the guidance to demonstrate MASH compliance.
The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers should develop and include in their proposal a detailed research plan for accomplishing the project objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meet the research objective.
The research plan should be divided into tasks, and proposers must describe in detail the work proposed in each task. The research plan should also include a description of proposed deliverables for each task or group of tasks along with a detailed project schedule. Deliverables should include an interim report prepared approximately half-way through the project that describes work completed in early tasks. This interim report should also include an updated work plan for remaining tasks and an annotated outline of the final report deliverable(s); NCHRP approval of the interim report is required prior to proceeding with subsequent tasks. The interim report will be presented at a face-to-face meeting with the NCHRP project panel. The research plan should also include an appropriate number of web-enabled teleconferences (including one within 1 month of the contract’s execution date). NCHRP will host the web-conferences and provide the meeting venue either in Washington, D.C. or Irvine, CA for the face-to-face meeting with the NCHRP project panel.
Final deliverables should include:
Documentation of the research effort;
Stand-alone guidelines, including any drawings, system designs and/or specifications in a format suitable for consideration by AASHTO for use in a future update to the Roadside Design Guide (RDG), and format suitable for inclusion in the Task Force 13 On-line Guide;
Documentation of recommended MGS placement configurations, simulation model results, and ISO 17025 crash test results including videos in a format that can be used by a state department of transportation to illustrate MASH compliance;
For systems considered to be MASH TL-3 compliant, provide a justification summary including test data and deflection reduction effectiveness that could be used by the states for system implementation; and
Recommendations for additional needed future research.
A PowerPoint presentation with speaker notes suitable for a varied audience that summarizes the project describing the background, objectives, research method, findings, and conclusions.
Note: Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the final deliverables.
STATUS: Research in progress.