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Bob, I was wondering if I could take a little bit of your time this morning to talk about ZOI and foundations for sign trusses that are in line with a barrier, median or outside.  The question is, whether or not to taper up to 54” on foundations that are taller than 54”.  I am thinking 54” rather than 48” (mentioned in one of INDOTs previous questions on light pole placement) because of the recommendation given in AASHTO for barriers within 10 ft of a bridge pier.

Our median barrier is 45” tall and there are foundations 72” tall in line with the median barrier.  Is there benefit in tapering the 45” median barrier to 54” at that 72” foundation?  It seems there would be reduced snag but is there a point where you just accept snag and not taper the height of the wall?

I have been reading through some of the Q&As on the topic of ZOI but for some reason I am not able to apply what is being said to this situation.  Maybe I was reading the wrong Q&A?

I think that the general guidance we discussed previously still hold true here. For 45” tall barriers, there would still be a snag concern with respect to passenger vehicles as you approach a 72” tall foundation.

Tapering the barrier vertically to 54” would largely eliminate concerns for ZOI and contact with the foundation for passenger vehicles.

In order to reduce ZOI and snag concerns for heavy trucks, the height would have to be increased more significantly. It is very difficult to mitigate ZOI for heavy vehicles completely based on barrier height alone.

Let me know if that helps and if you have any questions.

Thanks!