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What is the allowable post length for the crash tested options for thrie beam guardrail systems? We wlould like to know what post length is acceptable beyond post 9/10 in bullnose. We would like to use 6 ft.

We reviewed the prior research and found that three different thrie beam configurations have met the 350 safety standards. They are listed below. Upon inspection, it would seem appropriate to maintain the use of 6.5 ft long posts for the standard wood post thrie beam guardrail.

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Summary

1.       Standard Thrie Beam (G9) system did not pass 350 - 6.5 ft W6x9 posts with 21.5" long W6x9 blockouts w/ 32" rail height

2.       Modified Thrie Beam = 6'-9" long W6x9 posts with 49.5" embedment and 18" deep M14x18 blockouts w/ 33.6" rail height

a.       Tested to TL-3 and Tl-4

3.       Thrie beam with 6'-9" long W6x9 posts with 49.5" embedment and 6"x8"x21.8" long routed wood blocks passed NCHRP 350 w/ 31.65" rail height

4.       Thrie beam with 78" long 6"x8" SYP posts and 6"x8"x21.8" long routed wood blocks passed NCHRP 350 w/ 31.65" rail height

Short answer, 81" long posts for steel and 78" long wood have passed.