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Departing End Structure for MGS with Curb

State IL
Description Text

IDOT uses a guardrail attachment
to the downstream end of a structure on a one-way road that attaches the w-beam
to 1 inch diameter by ~2 ft anchor bolts cast into the concrete
structure.  Is it acceptable to use a curb with this guardrail near and up
to the structure?  (See attached Highway Standard “218-631026-06 TrafBarTermType5.pdf”).

  • Guardrail
Other Keywords Departing end anchorage, MGS, curb
Date April 5, 2016
Attachment 218-631026-06_TrafBarTermType5.pdf


To my knowledge, guardrail anchorages such as this have never been crash tested.  As such, I will comment on the system assuming that the upstream anchorage is crashworthy and wouldn’t negatively affect the guardrail system.

 The MGS placed 6” behind a 6” tall curb was successfully evaluated to NCHRP 350 standards – see report TRP-03-139-04.  Assuming your upstream anchorage doesn’t affect the performance of the guardrail system, then the behavior of the MGS with curb should also be crashworthy to NCHRP 350 standards.

 One side note here – recent testing with MASH small cars has raised concerns about possible rail tearing when small vehicles impact a curbed MGS installation (the NCHRP 350 evaluation did not include a small car).  This issue has been brought to the Pooled Fund Sponsors’ attention, and a MASH evaluation (including the small car) is currently a potential project for the 2016 Pooled Fund Program.  Thus, we may learn more about the crashworthiness of the MGS with curbs in the near future.  Until then, I can only say that the MGS with curbs has been NCHRP 350 approved.

Date April 5, 2016

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