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Kentucky is considering reducing the minimum guardrail length shown in our Standard Drawings. After reviewing your report Minimum Effective Guardrail Length for the MGS, it appears that the minimum effective length is 75 ft. The report notes that the testing did not evaluate different end treatment configurations. As we consider how the MGS run interfaces with end treatments in practice, we would like to confirm how the 75-ft length is defined. Specifically, is the 75 ft measured from length-of-need to length-of-need (post to post)?  Any additional guidance or insights you may have would be appreciated. 

For the minimum length MGS, we research and tested the shortest redirective length for the MGS based on simulation. It was found that a 75’ length from end anchor to end anchor worked acceptably when impacted at the 4th post downstream of the upstream end anchorage.

A related study on downstream anchoring found that the MGS can redirect the pickup truck when impacting at least 6 posts upstream of the downstream end anchor. That study also provided hazard locations based on distance from the downstream end of the system.

https://mwrsf.unl.edu/researchhub/files/Report279/TRP-03-279-13.pdf

Based on these studies, the redirective length of the MGS for a 75’ system would be limited and would be shorter than the 75’ system length. For a 75’ long system, that leaves only 25’ or so of true redirective barrier length.

For longer MGS systems, almost all proprietary end terminals have shown redirective performance at post no. 3. Some tension-based terminals are even farther upstream than that.

Let me know if that answers your question. Happy to discuss further.

Thanks!