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Can
you quickly tell me if it has been put in writing from anyone that for the
following two special designs which MWRSF tested that either size block may be
used:

1. 
Long span design (2 or 3 posts omitted)

2. 
Curb and MGS combo (up to 6" behind a 6" curb)

As
to 1. above, I know you have responded to Shawn Dedenham of UDOT that using
12" blocks only on the CRT posts should be fine.  But I'm seeing a
lot of standards in similar states using 8" blocks for their standard that
these two special designs are also shown with 8" blocks.  Your 187
report makes no comment about allowing an 8" block.  I thought
Q&A 1268 was going to get to it but only related to the steel vs CRT post
(don't know what ME has in their standards).

Would
appreciate your info.

The original MASH evaluation of the MGS long span occurred before testing the MGS with 8” blockouts was completed, and the MASH TL-3 testing of the MGS long span was conducted with 12” deep blockouts. With respect to the MGS long span system, we have noted that the shorter 8” blockout are likely acceptable in the MGS long span system. Although the system has not been evaluated to MASH with the shorter 8” blockouts, the general performance of MGS systems that have been tested and evaluated with both blockout depth options have been similar enough to suggest that the performance of the MGS long span system would be similar with either blockout as well. As always, this recommendation comes with the caveat that crash testing is the best option to truly determine the efficacy of the 8” blockout depth with the MGS long span and the recommendation is based on our best engineering judgement at this time. Thus, it may be refined as new information and research becomes available.

In terms of the MGS installed 6” behind a 6” tall Type B curb, all of our MASH TL-3 curb testing has been done using 12” blockouts as well. As with the MGS long span, we expect that the shorter 8” blockout are likely acceptable in the MGS with curb system. Although the system has not been evaluated to MASH with the shorter 8” blockouts, the general performance of MGS systems that have been tested and evaluated with both blockout depth options have been similar enough to suggest that the performance of the MGS long span system would be similar with either blockout as well. As always, this recommendation comes with the caveat that crash testing is the best option to truly determine the efficacy of the 8” blockout depth for the MGS with curb and the recommendation is based on our best engineering judgement at this time. Thus, it may be refined as new information and research becomes available.

We have not recommended the use of non-blocked post in the immediate area around the unsupported span of the MGS long span or with curbs due to differences in the vehicle snag on the barrier post that has been observed in non-blocked MGS systems. Recommendations for the MGS long span and MGS with curbs and with non-blocked posts is located in MwRSF Report No. TRP-03-262-12. We do know that the performance of guardrail systems is affected by shorter blockout lengths, but it is not clear what the limits of the barrier performance is at this time without further study.

Thanks