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We have been trying to upgrade
some of our W beam guardrail with the minimal impact to the foot print
possible.  For a very long time we place 56 feet of rail on the end of our
bridges.  Now as we go back to update them we are trying to update the
systems to our current standard.  Our newer system is much long and can
require significant grading in environmentally sensitive areas near
bridges.  One of our designers asked if we could use the BA-201(25’) with
the BA-206 (37.5’) for and overall length of 62.5’.  I know it is
desirable to have another 25’ of tangent between the 2 pieces but wondered on a
special situations if we could go to that minimum length

http://www.iowadot.gov/design/SRP/IndividualStandards/eba201.pdf

http://www.iowadot.gov/design/SRP/IndividualStandards/eba206.pdf

First, in the BA-201 drawing there should be 1 more 6-ft long post upstream of the w-to-thrie transition piece at a 37.5” spacing.  This also moves the post locations away from splices for the MGS. Don’t know if that post is considered a part of the standard MGS (so it’s on another drawing set), but I figured I would mention it.

Your BA-601 plan shows the option for a curb under the transition.  Recall, if a curb is present, then the guardrail placed immediately upstream of the w-to-thrie transition segment nested needs to be nested for 12.5 ft (refer to report TRP-03-291-14).  You should note that in your drawing set.

Finally, there are recommendations for the necessary length of guardrail upstream of the transition within the conclusion sections of reports TRP-03-291-14 (page 137) and TRP-03-210-10.  These reports are available on our website (mwrsf.unl.edu). Note, the recommendations are identical in reference to the W-to-thrie transition segment.  Please refer to these recommendations as there are different criteria for (1) total length, (2) terminal length, and (3) length prior to a guardrail flare. 

Let me know if you have further questions.