Need to Re-Lap Guardrails in Work Zones

#9687 March 23, 2023 Brad Julian ( [email protected]) New Mexico

NMDOT specs require guardrail to be overlapped in the same direction as the direction of traffic in the nearest lane for permanent construction. In the past, there was a requirement to re-lap guardrail in work zones if the direction of travel had changed (i.e. NB and SB traffic both on NB lanes). That requirement has disappeared from our specs and drawings and I’ve received some questions from field staff on whether NMDOT should still require the re-lapping. Is there any testing on reverse impact of guardrails? I see some for end treatments but not necessarily on the guardrail itself.

  1. Nauman Sheikh ( )

    Regardless of the lapping practice, guardrail splices can be hit in both directions. Lapping guardrail splices with the exposed rail edge located in the downstream direction of the adjacent traffic is generally a good practice. It should be retained for new installations and, whenever possible, for repaired installations. Keeping the exposed edge of the guardrail in the downstream direction of the adjacent traffic minimizes the potential for vehicle wheel or door snagging.

    It should be noted, however, that both rail segments are tightly connected at a splice location. Both rail elements have same lateral stiffness. For these reasons, the two connected segments move together with very little potential for large separation at the splice during vehicle impact. This reduces the chance of a severe vehicle snag. While it is generally a good practice where practical, lapping splices in the manner described above may not be a critical requirement for the guardrail to function properly.

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