The introduction or removal of roadway geometric features has shown to cause critical differences in safety performances for some barrier systems. Approach guardrail transitions (AGTs) in particular have been shown to fail crash tests after a curb is either introduced or removed from otherwise crashworthy systems, as demonstrated in the noted report (TRP-03-291-14) and in other AGT tests. In addition, the termination or transition between adjacent features can cause their own issues with system crashworthiness. Thus, to be conservative and avoid any potential snag and/or stability issues, we have recommended that the curb (or lack thereof) be consistent through the critical area of this MGS stiffness transition – specifically the area under and upstream of the W-to-thrie transition segment. That has produced the following recommendations:
1. If you want to terminate the curb within the AGT system, we recommend doing so prior to the W-to-thrie transition element (or as you stated, before post 11 – from TRP-03-291-14 page 74).
2. If the curb needs to be carried further than this location, we recommend carrying it past the entire AGT system. This extends another 18 ft – 9 in. to the upstream end of the nested W-beam rail (or the mid-span between post 6 and 7 from trp-03-291-14 page 74).
Terminating or transitioning within this 18.5-ft region of the AGT may be crashworthy, but we simply don’t have the research or testing to confirm that.
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