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Can we use plastic blocks on post 9 and posts beyond post 9 in the thrie beam bullnose.

Standard 31” tall thrie beam (G9) has not met MASH with full height blockouts. It failed MASH TL-3 in testing at TTI. There are two 34” tall systems that have met MASH, but both use a shorter or tapered blockout rather than full height. We noted issues with full height blockouts in thrie beam AGTs in the past as well. This is the reason that the bullnose has always employed shorter, tapered blockouts as far back as the NCHRP 350 versions of the barrier.

In terms of your question, there would be concerns regarding the use of full-height plastic blocks with thrie beam guardrail. While no testing has been done to date on 31” tall thrie beam with shortened blockouts, we would expect it to have acceptable performance based on the performance of the MGS and the 34” tall thrie beam system that have met MASH. As such, we would recommend using shorter blockouts beyond post no. 9. Shorter, plastic blocks that have previously been considered crashworthy would seem to be a reasonable substitute for shorter wood blockouts.

Thanks!