View Q&A

We have been contacted by Gibraltar about requiring the maximum post spacing of cable barriers being 15'.  We based our 15-foot maximum post spacing (as many other states have) on an FHWA memo.  Gibraltar has provided me with an email from the FHWA indicating that 20 foot spacing is O.K. based on crash testing. 

Gibraltar is also indicating that it and other manufactures of HTCG believe that close post spacing leads to underrides.  I was wondering what is MwRSF's opinion on post spacing and if narrower post spacing is leading to under rides?

Also we have required that the fittings for our cable barrier project have a minimum breaking strength of 39,000 lbs.  Gibraltar is indicating that there are no fittings that meet the 39,000 lbs breaking strength.  They do indicate that the 1-inch fittings have a 36,000 lbs breaking strength.  They are also indicating that they have miles of cable barrier with 3/4-inch fittings (breaking strength of 26,000 lbs) that are working fine.

Personally, "a chain is only as strong as its' weakest link" is my theory (i.e. use 1-inch fittings) and I believe Dr. Faller and I have exchanged some emails on this topic.  However, with information about cable barrier changing so fast, I wanted to make sure that I had the most current research on this topic.

1.   I strongly disagree with Gibraltar's opinion about close post spacing leading to under ride. In fact, I believe just the opposite, long post spacing is likely more to lead to under ride. I would like to hear any support they have for such a claim. ALthough we recommend a 16' maximum rather than 15', I think that in this range, shorter is generally better.

2.   Couplers (splice components) rated at 26,000 lbs are too weak.
We have tested these and they are much weaker than the cable.
We tested Bennet Bolt's non-proprietary, reinforced couplers and found them to be as strong as the cable system (about 40kip dynamic).

3.   The 3/4" end fittings are also too weak.

4.  Make sure you specify that all connections should have strengths comparable to the cable, about 38-39Kips. These could be dynamic strengths, if necessary.