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My question is can you use an 8” block out on a Barrier Transition Section (attached).  This substitution is not critical, the thought was it would clean up the look and make everything easier to lay out.

Please let me know your thoughts.

We currently recommend the use of 12” deep blockouts starting at the first posts at ½ spacing upstream of the w to thrie beam transition section through downstream into the first 4 posts in the ¼ post spacing. In our testing of the upstream stiffness transition under MASH TL-3, we observed significant wheel snag with the small car and pickup truck on the posts in the area where the vehicle engaged in the ½ post spacing. As such, we have been cautious about reducing blockout depth in that region. You do have the blockouts shown as shorter. We do recommend the use of shorter blockouts in the thrie beam region to prevent vehicle instability. For the wood blockouts, these are typically 18”-19” tall. It appears you are using these. I marked these on your detail.

We have no reservations about using 12” blockouts rather than 8” ones in the nested thrie beam region adjacent to the bridge parapet.

Let me know if that answers your question or if you need something else.