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We have a project under construction where a low-tension cable barrier was installed over a concrete box culvert and the contractor was not able to drive 2 posts deep enough before hitting the box culvert. The contractor installed the rest of the system leaving a 12’ post spacing on top of the box.

Has there been any testing of a low-tension cable barrier with one or two posts removed? I’m assuming culvert mounted posts have not been tried on a cable guardrail system?

Our standard plan (see attached) also shows 4ft as the minimum spacing with 16’ post spacing as the maximum. I’m not sure where this maximum came from, is this based on any MASH testing?

I hate to tell them to remove it and install a W-beam system since its already out there, so I’m looking for any possible options.

Thanks,

The low-tension cable barrier used by NDOT has not been tested to MASH at this time. The original design was tested under NCHRP 350. It used a post spacing of 16 ft. https://static.tti.tamu.edu/tti.tamu.edu/documents/FHWA-RD-98-046.pdf

Subsequently, we tested the system with a 4’ post spacing offset from a steep slope for NDOT - https://mwrsf.unl.edu/researchhub/files/Report110/TRP-03-155-05.pdf

For a level terrain installation, the 16 ft post spacing would still be compliant with the system originally tested under NCHRP 350.

If you are using the 4’ post spacing version adjacent to slope, there may be issues with removing posts in the system in that the deflection would go up in that region and may compromise vehicle capture and stability. For a level terrain installation, the 12’ omitted post region would be less of a concern. Deflections would go up, but the stability and capture concerns are not an issue if the vehicle is not interacting with a slope.

If you need to have those two posts in place, we have developed several options for mounting S3x5.7 posts to culverts and culvert headwalls that would be viable options for use with these cable posts. Several of those are outlined in the attached paper.

Let me know if you have any questions.

Thanks!