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Could you please review the attached information – going back to 1979 – in regards to 7” hole location within the tested G4/MGS guardrail posts? Could we have a discussion on this matter, as it would seem that the 7” dimension is not consistent with the what the industry has been providing for several decades.

Perhaps something as simple as issuing a letter indicating this has been reviewed and that there is a +/- 1/8” tolerance which is applicable? Or accepting that the NJDOT drawings themselves indicate that the dimensions are subject to manufacturing tolerances and this 7” to 7-1/8” is one such tolerance?

Key items:

June 1979 drawing from TF13

• Various more recent TF13 drawings indicating the dimension is 7”.
  
  
  • As information, TF13’s sole purpose is to “standardize safety hardware”.
  
  
  • These are PWE04, PWE01-02, PWE01a, and PWE03. Their website is: https://tf13.org/components/
  
  
  • Please also note that the hole is 13/16” and a 5/8” bolt goes through it …
  
  
  • Please also note that standard manufacturing tolerances (“accepted manufacturing practices”) apply to the post (see page 2 of the drawings).
  
  
  
   
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• MwRSF Report TRP-03-276-13:
  
  
  • On page 24, figure 10 – it shows the 7-1/8” dimension. HOWEVER, on page 133 there is a Certificate of Compliance indicating “545G” were utilized in the testing.
  
  
  • The Trinity Highway Products drawing for a 545G is attached – showing the hole was at 7".
  
  
  
   
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• MwRSF Q/A on this topic:
  
  
  • ID=1127 – indicates that 7” or 7-1/8” is acceptable.
  
  
  • As information – the 7-1/8” dimension seems to have been introduced when metric dimensions were briefly utilized by some agencies, etc. However, the industry still has been manufacturing these to the TF13 drawings.
  
  
  • Even NJDOT CD-609-2.1 (BDC17D-02 Attachments) Sheet 11 of 42 in Note #1 indicate that “all dimensions are subject to manufacturing tolerances”.

• Providing a 13/16” hole, 7-1/8” from the top of the post and utilizing a 5/8” post bolt to secure it provides a lot of vertical sag opportunity for the rail panel – which itself also has an oversized slot (vertical and horizontal = 3/4”H x 2-1/2”W).

 

I have also copied Mr. Bielenberg of MwRSF, for any additional input / insight he may have. Bob?

• I am aware that NJDOT is a member state of the MwRSF Pooled Fund.

 

We have had similar questions in the past regarding slight dimensional differences on holes in guardrail posts. Please see the response at the link below that addresses some of these issues. It may provide some additional information relative to the discussion below.

https://mwrsf.unl.edu/q&a/view.php?id=1127

Thanks!