Development of MASH TL-3 Deflection Reduction Guidance for 31-inch Guardrail

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 National Cooperative Highway Research Program (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 was 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.


  • English


  • Status: Completed
  • Funding: $499429
  • Contract Numbers:

    Project 22-38

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Jared, David

  • Performing Organizations:

    Texas A&M Transportation Institute (TTI)

    400 Harvey Mitchell Parkway South
    Suite 300
    College Station, TX  United States  77845-4375
  • Principal Investigators:

    Kovar, James

  • Start Date: 20190708
  • Expected Completion Date: 20230915
  • Actual Completion Date: 20230915

Subject/Index Terms

Filing Info

  • Accession Number: 01672563
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 22-38
  • Files: TRB, RIP
  • Created Date: Jun 19 2018 12:43PM