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For the older G4(1S) or G4(2W) systems installed at the original metric height (27.75”) we don’t believe that a 6” offset of a post should make a substantial effect on barrier performance. However, at some point, the alternation of the post spacing may become more of an issue due to the potential for pocketing, vehicle snag on the posts, and vehicle instability.

We believe that a 1 ft offset tolerance on guardrail post longitudinal placement is acceptable in discrete locations. We would not recommend throughout a system. Typically, we would expect the posts to be placed such that the tolerance provided by the rail slots would be sufficient for attachment of the guardrail. However, a single post offset 1 ft or less should not pose an issue in our opinion.

It should be noted that some care should be taken when field cutting a new post bolt hole such that stress concentrations that may reduce the rail capacity do not arise. Thus, the post bolt hole should be cut smoothly and correspond with typical post bolt hole dimensions. Additionally, we would recommend spray galvanizing the hole to prevent corrosion.

For the MGS system, we have successfully tests a single omitted post at standard post spacing under the MASH TL-3 impact conditions. Thus, for the MGS system, the tolerances and may be larger and/or the post may be simply omitted in that area. The report on that research should be out shortly.