View Q&A

I
was asked how close can a underground obstruction be to a beam guard
post.  I search your web site and incorporated some of that guidance into
the drawing above. 

I
did not know how close a parallel underground obstruction could be from a
post.  So I tried to use some of the guidance from the mow strip Research
to develop this drawing. 

What
do you think?

I think your minimum offsets are justifiable.  I have a few comments:

TTI conducted full-scale crash testing on  guardrail systems with 18”x18” leave-outs. The posts were offset 3” from the front of the leave-out.  Thus, there was 9” of leave-out located between the back of the post and the back of the leave-out.  You can reduce your minimum “X” and “Y” distance to reflect 3” and 9” gaps in front and behind the posts, respectively.

We have recommended that MGS posts have a minimum of 6” gap between the side of the post and a rigid hazard..  Accordingly, you could reduce the minimum “Z” distances to 6”.

If a hazard is located closer to a post than these limits, you should consider omitting a post.  Omitting a single post within an MGS installation has been recently proven crashworthy.  Guidelines for often a post can be omitted were included in the project report, TRP-03-326-16.