Design Guidelines for TL-3 through TL-5 Roadside Barrier Systems Placed on Mechanically Stabilized Earth (MSE) Retaining Walls

NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features and its successor, the AASHTO Manual for Assessing Safety Hardware (MASH), define impact performance criteria for roadside barrier systems. These documents define six different test levels of increasing impact severity that incorporate varying impact speeds and vehicle types. These test levels provide a basis for establishing warrants for the application of roadside barriers for roadway facilities with different levels of use (i.e., service levels). NCHRP Project 22-20, Design of Roadside Barrier Systems Placed on MSE Retaining Walls, published as NCHRP Report 663 under the same name, developed guidelines for designing the barrier moment slab and mechanically stabilized earth (MSE) wall to withstand vehicle impact loads. However, the scope of the project was limited to passenger vehicle and light truck impacts and did not include consideration of large trucks. Highways with a significant percentage of truck traffic often employ higher test level barriers. The interaction and impact loads associated with large truck impacts are substantially different than those associated with passenger vehicle impacts. The magnitude of the impact load for a Test Level-5 (TL-5) truck impact is significantly greater than the load associated with the 5,000-lb pickup truck that is the design vehicle for TL-3. Further, the height of the applied load is much greater for a TL-5 impact, and the articulated nature of the tractor-van trailer results in three distinct impact events with the barrier. It is estimated that 10 million square feet of mechanically stabilized earth retaining wall is constructed annually in the United States. Most MSE retaining walls used in highway fill applications are constructed with a roadside barrier system consisting of a traffic barrier connected to a below-grade moment slab or foundation. The moment slab is intended to provide stability to the barrier system during an impact and reduce the influence of barrier impact loads on the underlying retaining wall system by distributing the load over a wide area. Current procedures and design details for roadside barriers placed on retaining walls vary widely among state highway agencies. Additional research is needed to enhance our understanding of the behavior of an MSE wall and barrier foundation when subjected to large truck impacts. Developing guidelines for the use of truck barriers on MSE walls will permit the development of more relevant and cost-effective designs for the barrier foundation and MSE wall. This research will extend the work accomplished under NCHRP Project 22-20 and eliminate the need to extrapolate knowledge from a TL-3 impact to a TL-5 impact. The objective of this research is to develop, in a format suitable for consideration by AASHTO, recommended guidelines for designing roadside barrier systems placed on MSE retaining structures to resist vehicular impact loadings varying from passenger vehicles to heavy trucks. To extend the work done under Project 22-20, this project will consist of engineering analyses, computer modeling, and bogie testing for Test Levels 3 through 5 and will include full-scale crash testing of a tractor-van trailer (TL-5) into a barrier placed atop an MSE retaining wall. The guidelines should address Test Levels 3 through 5. Specific considerations include defining appropriate design loads, developing procedures for sizing the traffic barrier foundation, and designing the MSE wall when traffic barriers are required.


  • English


  • Status: Active
  • Funding: $610000
  • Contract Numbers:

    Project 22-20(02)

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

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

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Bush, Mark

  • Performing Organizations:

    Texas A&M Research Foundation, College Station

    Texas A&M University
    College Station, TX  United States  77843
  • Principal Investigators:

    Bligh, Roger

  • Start Date: 20100514
  • Expected Completion Date: 20170531
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01464180
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 22-20(02)
  • Files: TRB, RiP
  • Created Date: Jan 3 2013 2:37PM