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Mid-America Transportation Center

Testing and Evaluation of Guardrail Posts Installed in Mow Strips

Final Report
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Researchers

  • Principal Investigator: Scott Rosenbaugh (srosenbaugh2@unl.edu 402-472-9324)
  • Project Status
    Complete
    About this Project
    Brief Project Description & Background
    Often times, it is desirable to place longitudinal concrete slabs or continuous asphalt pavements underneath W-beam guardrail systems to reduce time and costs for mowing operations around the guardrail posts. Unfortunately, the placement of guardrail posts within these mow strips restricts the posts from rotating, and negatively affects the safety performance of the barrier system by increasing the risk for rail rupture. Additionally, the impact forces transferred through standard guardrail posts into the mow strip often result in pavement damage that requires costly repairs. This project seeks to develop a W-beam guardrail system applicable for installations in rigid mow strips that minimizes damage to the pavement while also satisfying safety performance standards.
    Research Objective
    The objective of this research project is to develop a W-beam guardrail system for use in mow strips and other pavements. The barrier must satisfy the safety performance standards contained within the Manual for Assessing Safety Hardware (MASH). Additionally, damage to the mow strip must be minimized, such that repair work to the pavement is not required after vehicle impacts. The performance of the new system design will be evaluated and verified through a combination of dynamic component testing and full-scale vehicle crash testing conducted in accordance with MASH.
    Potential Benefits
    The development of a W-beam guardrail for use in rigid pavements will allow roadside designers to install guardrail in mow strips without affecting the safety performance of the barrier. The new guardrail design will also minimize the risk of pavement damage. Thus, the new guardrail and anchorage design will significantly reduce labor and system costs associated with the installation, repair, and maintenance of barriers installed in rigid pavements.
    Abstract
    During an impact event with a W-beam guardrail system, post rotation through the surrounding soil accounts for the majority of the energy dissipation. When guardrail posts are installed in pavements or mow strips that restrict rotation, the amount of energy dissipation is reduced, and the rail is subjected to increased forces. This scenario negatively affects the safety performance of guardrail systems by increasing the risk of rail rupture and vehicle penetration. As a result, it is recommended that strong-post guardrail systems installed in mow strips utilize a blocked-out area or “leave-out” in the pavement around the base of the post. Recently, the Midwest Guardrail System (MGS) Bridge Rail was developed utilizing S3x5.7 posts instead of the standard W6x9 guardrail post. These weak posts were placed in rigid sockets attached to the bridge deck and provided energy dissipation through plastic bending instead of rotation through soil. The MGS Bridge Rail was successfully full-scale crash tested, and showed promise as a weak-post design for other applications. The Midwest Roadside Safety Facility (MwRSF) has an existing project to adapt the MGS Bridge Rail for use in mow strips and other rigid pavements. That project has funding to evaluate design concepts through dynamic component testing and to conduct a full-scale crash test of the selected design. However, further research is needed to evaluate various mow strip configurations and their effects on system performance and damage when coupled with a weak-post guardrail system. Therefore this proposal seeks to supplement the concept development of installing weak posts in mow strip pavements through dynamic component testing.
    Project Amount
    $ $60,000