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We are considering the use of asperities in a concrete bridge rail and have used NCHRP 554 as guidance. 

A TL-2 test condition will help some to mitigate snag risk. One thing to note is that the NCHRP Report 350 criteria used a small car impacting at a 20-degree angle, while the MASH criteria use a small car impacting at a 25-degree angle. Any snag risk with small car may be accentuated with a 5-degree angle increase.

At the end of the rail near posts, do you have a 2" recess with a sharp 90-degree angle coming forward? Or, do you have tapered ends on upstream and downstream ends of longitudinal recessed region?

The 2” projection on the bottom is the MnDOT standard “brush curb” that runs longitudinal with the barrier with no disruptions. The vertical posts are projected 1” at 90 degrees and what I didn’t mention in my first email is that we are changing these to include 45 degree bevels on both the upstream and downstream ends to comply with the Caltrans guidelines (included at the end of the NCHRP 554 report).  

You note that the post face to recessed rail face is only 1 in. where the interface will now include a 45-degree bevel on both side of post. For now, that may be an option until further MASH data comes forth. We may have some Hawaii DOT bridge rail testing in future that may help update on knowledge under MASH. Thanks!