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A regional engineer has a project where the roadway profile is zero and they need to install concrete barrier (they will have extreme difficulties providing longitudinal drainage on the median shoulder).  The regional engineer wants to place an opening in the concrete barrier wall to provide roadway drainage. 

Regional maintenance staff has indicated that they want to have an 8" tall and 18" wide opening (so they can fit a shovel into the opening and clean it out).  I have indicated that this size of opening is not preferred because it could cause a vehicle to snag or roll over during impact. 

Setting aside MwRSF's concerns about barrier reinforcement, has there been research into geometry drainage openings that go through concrete barrier? 

In addition, some engineers are adjusting the front lower face of the barrier to accommodate drainage inlets.  Has there been study on how to adjust the front face of concrete barrier to account for drainage inlets?

For vertical-face parapets, the inlet opening that you note may be manageable as long as the steel reinforcement above and adjacent to the opening was adequate and the small car doesn't snag on the downstream edge of the opening. A 4 to 6-in. opening height would seem reasonable for vertical parapets. For safety shape parapets, this opening size may be extreme and accentuate small car wheel snag. A 3-in. tall opening may seem reasonable for safety shape parapets. However, I am unaware of any research devoted to designing safe inlets for crashworthy barrier applications.

Actually, this may be another reason for moving Wisconsin closer to using vertical, or near vertical, concrete parapets.