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New MGS Transition and Wood Post Inventory

State IA
Description Text

Would you be able to provide me with the latest drawings of the simplified MGS bridge transition?


Also, I have had a question arise from our parts warehouse regarding 8x8 wood posts and blockouts.  Is there still a need for us to stock these, or can we replace any 8x8 wood post and/or blockout with a 6x8 version instead?  If so, could we replace only one at a time, or would we need to replace all posts and blockouts within the installation at the same time?

  • Approach Guardrail Transitions
Other Keywords none
Date May 11, 2009


I am copying this email to Karla so that she can direct a MwRSF staff member to get you the latest approach guardrail transition detail for the MGS attached to a thrie beam transition that utilizes a half-post spacing. In the future, MwRSF will provide details on how to adapt the noted transition to thrie beam transitions that use a quarter-post spacing.


With regard to wood posts and blockouts, MwRSF is still evaluating the appropriate wood post size and length for use as a substitute in the simplified, steel-post, stiffness transition. Results from this component testing and analysis should be available within 2-3 months.


As noted at the spring Pooled Fund meeting, 6"x8" by 6' long wood posts have been approved for use in the MGS as a substitute for the W6x9 by 6' long steel posts. Although we are confident of their use in the MGS, we were hopeful that the Pooled Fund group would fund the 2270P crash test. Unfortunately, that funding did not come to fruition in the recent meeting due to a prioritization of other projects, such as cable barrier projects. At any rate, Iowa could begin to implement the standard wood post size into the MGS based on the prior FHWA acceptance of the MGS. In addition, Iowa could also implement 6x8 blocks standard guardrail utilizing the 8x8 posts at any time. However, it would be acceptable to use the 6x8 blocks with metric height W-beam rail using 6x8 posts. Finally, you would want to use 6x12 blocks for any MGS installations using W6x8.5 and W6x9 steel posts, or 6"x8" wood posts.

Date May 12, 2009
Attachment MWT-SP_R4.pdf

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