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Downstream Anchoring Requirements For The Midwest Guardrail System




Mario Mongiardini, Ronald Faller, John Reid, Dean Sicking, Cody Stolle, Karla Lechtenberg (Polivka)




Most state Departments of Transportation use simple adaptations of crashworthy guardrail end terminals as downstream anchorage systems, which typically include breakaway posts and an anchor cable. The safety performance of these downstream anchorage systems, when struck in reverse-direction impacts, is not well-known. A research study was proposed to analyze and crash test one trailing-end anchorage system involving a modified Breakaway Cable Terminal (BCT) terminal to the MGS guardrail. Bogie component tests were used to validate computer simulation models of the downstream end anchorage. Crash simulations with vehicles similar to the 2270P pickup truck and 1100C small car identified in the Manual for Assessing Safety Hardware (MASH) were used to determine (1) an effective critical impact point of the downstream system at the end of the length of need (LON) and (2) the location which maximizes the instability, snag, and wedging potential of a small car beneath the anchor cable. The end of the LON was defined as a downstream critical impact point (CIP) at which the terminal would no longer redirect an errant vehicle but instead gate and permit the vehicle to encroach behind the system. Two crash tests were conducted. A 5,172 lb (2,346 kg), 2270P pickup impacted the 6th post from the downstream trailing anchorage at 63.0 mph (101.4 km/h) and 26.4 deg, which caused the terminal to gate, and the vehicle proceeded behind the system. A second test, consisting of a 2,619 lb (1,188 kg) 1100C small car impacting the system 4 in. (102 mm) upstream of the 3rd post from the downstream trailing anchor at 62.0 mph (99.8 km/h) and 25.5 deg, resulted in acceptable redirection. Based on these crash tests and the simulations, recommended guidelines were provided for shielding obstacles behind the downstream anchorage of an MGS guardrail.


Highway Safety, Crash Test, Roadside Appurtenances, Compliance Test, MASH, Downstream Anchorage, Guardrail, Midwest Guardrail System (MGS), and Terminal

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