Across Australia and New Zealand, there are varying views on the placement of slip-based poles within the deflection zone of barrier systems. Historically, the consensus was clear: don’t do it – we don’t know how it will function, thus it’s not acceptable.
However, research by Pajouh et al. (2017) suggests otherwise. Their findings indicate that slip-base poles or shear-type posts are still likely to activate (i.e., shear off) even when located within the working width of a safety barrier. During the redirection process, impacting vehicles retain enough energy (at speeds of 30 to 50 km/h) to shear the post.
In response, Victoria has updated its Supplement to Part 6 with the following guidance:
“If a slip-base or other frangible pole type is considered appropriate for the location (i.e., based on speed and proximity to pedestrians), designers may locate slip-base poles within the working width of a barrier. The distance between the barrier and the pole should be maximised wherever possible, while considering factors such as accessibility, maintenance, and other asset-owner requirements.”
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Reference: Pajouh, MA, Bielenberg, RW, Schmidt, JD, Lingenfelter, J, Faller, RK, & Reid, JD (2017). Placement of Breakaway Light Poles Located Directly Behind Midwest Guardrail System (MGS). Midwest Roadside Safety Facility, University of Nebraska-Lincoln, Report TRP-03-361-17.
Video credit: Midwest Roadside Safety Facility
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