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My name is Tom Rhoads and I am a design engineer in Scott King's squad at the Kansas Department of Transportation. I've been assisting Scott with some revisions to our MGS Guardrail Standard Drawings. Throughout our revision process we have been communicating with Ray Schacht at Midwest Machinery Supply and a question has arisen regarding a KDOT Standard Specification indicating the blockouts we use for our guardrail systems should be planed prior to installation (I've attached a copy of the Standard Specification with the area of interest highlighted). Ray indicated once the blockouts are planed the resulting dimensions are 5 ½ inches to 5 5/8 inches by 7 ½ inches to 7 5/8 inches rather than 6 inches by 8 inches. Our question for you is: Is the reduction in the blockout section acceptable for MGS Guardrail installations?

Please let us know your thoughts.

MwRSF has successfully crash tested the MGS in blocked (12" deep) and non-blocked (no offset block but with backup plates) applications. In these testing programs, improved performance was observed when using the offset blocks. TTI later successfully crash tested the MGS with an 8" offset block. As a result of these programs, I would not get too concerned with minor deviations in the block dimensions when comparing full-sawn, rough sawn, and dressed blocks. As a matter of fact, some fabricators start the process with larger wood sizes so that the dressed block actually measures 6"x12" or 6"x8".

Previously, manufacturers and other State DOTs also inquired into the MGS block tolerances. Since similar inquiries have been made and responses have already been complied, I am forwarding to you information from the 2007 discussions with the Pooled Fund members states. Hopefully, my response above and the attached information will sufficiently answer your question.