View Q&A

I am contacting you on behalf of KDOT concerning some installation details for the FLEAT-MT (or similar product).  Our concerns deal mostly with the area in which the guard rail diverges from a single post, double sided block out configuration, to a separate post for each run of guard rail.

Attached are several drawings depicting two scenarios.

The first requires a non-standard length section of guard rail (fleat-mt.pdf, fleat-mta.pdf, fleat-mtb.pdf and fleat-mt.dwg) in order to provide post separation in this area.  (It should be noted that the drawings do not accurately depict the true post locations; the depth of the w-beam is not taken into account.)

The second (fleatrod.pdf) would require a large flare rate or the use of custom (larger than standard) block outs until separation is acquired.

Some questions include:

a)  How much separation is required between posts so that one post does not have an effect on the rotation of another post?

b)  What is your opinion of the use of non-standard guard rail lengths?

c)  What is your opinion of the use of custom block outs?

d)  Have you seen or studied any other configurations that you would recommend for use?

See my responses below. Note that there is no full-scale crash testing of any of these options and the following is based solely on engineering judgment. By copy of this e-mail, I will ask Bob Bielenberg to review my recommendations and place them in the pooled fund summary that goes out to all the states.

That said, I don't have a problem with what you have proposed.  I do have a few suggestions for your consideration in response to your question no. 4.

Let me know if you need further explanation.

Some questions include:

a)  How much separation is required between posts so that one post does not have an effect on the rotation of another post? I recommend at least 1 ft.

b)  What is your opinion of the use of non-standard guard rail lengths? - This is not a problem, provided the span is not greater than 9'-4&1/2".

c)  What is your opinion of the use of custom block outs? This is not a problem, provided the block is at least as deep as the tested block and is made of an acceptable material.

d)  Have you seen or studied any other configurations that you would recommend for use?

1.      You might want to consider inserting a more-or-less standard 2.86 m (9'-4&1/2") piece of rail where you have your current 2.195 m (7'-3") piece of rail. These pieces are generally available at most GR distributors.

2.      You might consider reducing the length of the tangent section, just upstream of the radius to about 4 meters instead of almost 8 m

3.      .If you don't like option 2, I would recommend that you consider mounting both guardrails on the same post for another 3.81 m (12'-6").