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In April of 2011 staff from MnDOT conducted a conference call with you and Dean Sicking to discuss a wide range of barrier design/geometry and crash testing related issues.  One specific issue we discussed was the taper at the end of concrete barrier sections, where the barrier transitions to a guardrail connection (see issue #3 highlighted in yellow in the first attachment).  The concluding statement for issue #3 includes the language (see first attachment), “End tapers for barriers taller than 34” should be modified to 1V:8H.”  We have adjusted the taper to 1V:8H for most of our barriers that are taller than 34”, but have a question regarding the MnDOT structural tube railing that was crash testing at your facility.  The second attachment is our standard plan sheet for the structural tube barrier, which has a height of 38”.  Please note the portion of the drawing in the upper left hand corner with the red border.  Should the taper on this shape also be modified to 1:8?  The current taper is 5:12, the same taper we use on all of barriers with a height of 34” of less.

Please let me know what you think.

Thanks!

A couple of comments on the detail you sent.

1.       We do believe that the concrete end section that you have shown in the detail should use the 8H:1V taper that we discussed previously for other concrete rail height transitions.

2.       A second comment should be made regarding the termination of the tubing adjacent to the increased height concrete end section shown. As the detail is currently shown, the vertical face of the concrete barrier at the end of the tube rail section poses a significant vehicle snag hazard for vehicles impacting from right to left as shown on the detail plan. We have been in discussions with other states that use similar end sections with their combination rails and have recommended flaring the vertical face of the barrier back and extending the tube section to mitigate the potential for vehicle snag at that location. I have attached a schematic showing the idea so you can get a picture of the type of modification we are suggesting.

Please contact me with any comments or questions.