|TTI Research Supervisor:
James C. Kovar, E.I.T.
Associate Transportation Researcher
Texas A&M Transportation Institute
College Station, Texas 77843-3135
|Pooled Fund Technical Representative:
Taya Retter, P.E.
Bridge Standards Engineer
Texas Department of Highways
125 East 11th Street
Austin, TX 78701
State Departments of Transportation (DOTs) provide a rail on top of concrete barriers to protect pedestrians from falling over the barrier. While this rail can provide protection for pedestrians, it can pose a hazard for motorists who errantly impact the barrier. Therefore, this rail is often located far enough away from the traffic side of the barrier to prevent vehicular interaction. The objective of this project was to determine the minimal offset required to locate a pedestrian rail on top of a concrete barrier.
The research team analyzed the videos from five MASH 3-11 crash tests to determine the maximum vehicle extension over the top of the barrier. This maximum vehicle extension was measured from the top traffic side face of the barrier, and the reference plane for each barrier is shown in the report. This measurement will provide guidance to the Roadside Safety Pooled Fund for the minimum offset distance to avoid vehicle contact with pedestrian rails placed on concrete barriers. The scope of the study was limited to MASH TL-3 and did not review with the vehicle extension distance for single-unit truck impacts under MASH Test 4-12. For those barriers having the minimum height to accommodate MASH TL-4 (i.e., 36 inches), the pedestrian rail offset distance needed to avoid vehicle contact would increase.
The Roadside Safety Pooled Fund can use the measurements listed in the table below to determine offset distances to avoid vehicle contact for pedestrian handrails under MASH TL-3 impact conditions. To minimize the chance for vehicle interaction with a pedestrian rail altogether, the vehicle extension values measured to the side view mirror would be appropriate to use. However, the side view mirror interaction with a pedestrian rail may not pose a significant risk. The side view mirrors are not typically a strong structural component of the vehicle, and they often fold inward if impacted. Therefore, states may elect to use the second set of vehicle extension values if the states desire to place the pedestrian rail closer to the roadway. Furthermore, pedestrian rails mounted closer than these values may still be MASH compliant. However, further evaluation would be needed to assess the effect of any vehicle interaction with the pedestrian rail. Lastly, the research team recommends more analysis in the future to corroborate these values because of the limited number of tests reviewed under this project.