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MGS Adjacent to 2:1 Slope - No blockout

Question
State NE
Description Text We have implemented the 9' post on the edge of a 1V:2H slope.


We have also implemented the standard post no blockout.


Could we combine these items?

Ex. Using a 9' post at the break of a 1V:2H slope w/o a blockout?

Keywords
  • Guardrail
Other Keywords none
Date March 1, 2012


Response
Response

I am copying my general thoughts that were recently provided for an identical inquiry about a month ago.

 

The MGS for 2:1 fill slopes was crash tested and successfully evaluated under MASH when installed with a 12" deep wood blockout and with the rail positioned at 31". However, the system was not successful when tested at 27¾". As such, we do not know the lower bound for this system variation when used with a blockout.

 

As you know, the standard blocked MGS has a "recommended" lower bound at 27¾" for new construction based on the successful MASH testing of the modified G4(1s). Note that we recommend that it be installed at its nominal height of 31".

 

MwRSF previously tested a non-blocked MGS under MASH when placed on wire-faced MSE walls with 6-ft long steel posts and backup plates at the slope break point of a 3:1 fill slope. MwRSF has also successfully tested a non-blocked, steel-post version of MGS with backup plates on level terrain under TL-3 of MASH.

 

Based on the testing noted above combined with engineering judgment and the best available information, we believe that a non-blocked version (with backup plates) of the MGS for 2:1 fill slopes could likely meet the MASH impact safety standards when installed at the 31" mounting height. However, it should be noted that no crash tests have been performed on this exact variation and that the lower bound would likely be affected, as was the case for the blocked version placed on 2:1 slopes with 9-ft long steel posts.

 

As a result and if deployed, it would be highly suggested that the MGS system only be installed with a 31" minimum mounting height when used in a non-blocked version on 2:1 fill slopes using the longer steel posts. Of course, the proven crashworthy system which utilizes the blockout would provide the safest alternative out of the two options.

 

In summary and based on the best available information, we believe that a non-blocked, 31" MGS with back up plates and 9-ft long steel posts at the slope break point of a 2:1 fill slope should also meet the TL-3 MASH impact safety standards. However, it has not been crash tested nor have we obtained FHWA acceptance for this variation.

 

Please let me know if you have any further questions or comments.

Date March 2, 2012


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