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MnDOT has a bridge project coming up that will requires installation of a TL-2 single-slope concrete barrier. The cross-slope on the bridge ranges from a 2% crown section to a 3.28% superelevation. The design speed is 45 MPH, and the horizontal radius is 1700’. I’ve attached our current guidance from our Memo to Designers #2020-01, which has some basis of recommendations from MwRSF, limiting the angle between the roadway surface and the vertical axis of the traffic railing to a maximum of 90 degrees (highlighted on pg. 2).

My question for you is – does limiting the vertical axis of our concrete single slope barrier to a maximum of 90 degrees from the roadway surface apply uniformly to all test levels? Or can that requirement be waived (or is it different) for a TL-2 application?

Let me know if you’d like to discuss/clarify anything further on a call. I would really appreciate your help here!

Thanks,

The previous guidance on the angle of the barrier relative to cross-slopes is still the best guidance we have.

In terms lower test levels, it would be rational to assume that lower test level applications with reduced speeds would be less prone to vehicle instabilities due to the angle of the barrier face. However, we don’t have any current research or analysis that can verify that is true.

As such, the best guidance we have for all test levels is likely the guidance we provided previously unless we can perform additional research to look at the lower impact severity cases.

Thanks!