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ODOT is designing a drainage inlet for an 81” single slope concrete barrier.  The proposed inlet is 12’ long with a 6” height.  In a previous Q&A (ID-228 Wildlife Crossing Holes in Barriers, MO, 5/2/2011) a 6-inch window was referenced as a maximum acceptable height.

This answer was published in 2011.  Any new developments or testing in this area that confirm the 6” height as acceptable?  Would flaring the inlet channel improve the crash performance?

What are your thoughts?

I think the original guidance we provided is still relevant.

The only new information I have found since then was related to NCHRP 350 testing of a TxDOT wildlife barrier opening in single slope. This appears to have met older criteria with a 12” opening, but it has not been tested to MASH.

Thanks!