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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.

Generally speaking, The states set the block tolerances they will accept based on their preferences. They may have additional considerations for the blockouts outside those we use in our design and testing procedures. In addition, any guidance we could provide is not “acceptance” in particular. Our comments would be based on our design and testing and our best engineering judgment, but would not provide acceptance or compliance with any type of standard.

Thanks 

Thank you for your response. I found it very helpful.

Based on your comment below, the MGS that has a block thicknesses between 8" and 12" will successfully pass the test. 

To clarify one point...your comments apply to guardrail that is utilizing a 'steel' posts...correct ?

One additional question: the MGS details illustrate nailing the block with a one double headed 16d nail through a 1/4" hole through the web of a steel post...to prevent the block from spinning. If a wood block manufacturer provides the block with a routed surface while maintaining thicknesses from 8" to 12" , is the depth of the routing considered a critical dimension to meet adherance to the MGS system as tested ?

I'll look forward to hearing back from you.

Thank you

See my comments below in red. 

Thank you for your response. I found it very helpful.

Based on your comment below, the MGS that has a block thicknesses between 8" and 12" will successfully pass the test.

This is true. The MGS has also been tested successfully without blockouts. Thus, shorter blocks would likely work too. However, we do not recommend shorter blockouts unless roadway width is an issue.

To clarify one point...your comments apply to guardrail that is utilizing a 'steel' posts...correct ?

The MGS has only been tested with reduced blockout depths on steel posts. We have tested several wood post versions of the system, but they have all had the 12” blockouts. Shorter blockout depths may work, but would likely need further investigation.

One additional question: the MGS details illustrate nailing the block with a one double headed 16d nail through a 1/4" hole through the web of a steel post...to prevent the block from spinning. If a wood block manufacturer provides the block with a routed surface while maintaining thicknesses from 8" to 12" , is the depth of the routing considered a critical dimension to meet adherance to the MGS system as tested ?

We have tested the blockouts nailed and with no nailing. For testing purposes, it makes little difference. Spinning of the blockout during a vehicle impact is not an issue. The nails and the routing are more of a in-service feature to prevent blockout rotation over time, as you noted. Thus, depth of the routing would have little effect on safety performance. However, if the routing was not sufficient to prevent block rotation over time on field installations, it would become an issue. I don’t have information on what routing depths are effective in the field. My suggestion would be to work with the state DOT’s to determine the depth that they prefer for the routing based on field experience.