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Phase I Assessment of Guardrail Length-of-Need




Daniel Albuquerque, Cody Stolle, Dean Sicking, Ronald Faller, Karla Lechtenberg




Guardrails have commonly been installed to prevent errant vehicles from impacting roadside hazards. However, guardrail impacts have contributed to numerous serious injuries and fatalities, are generally impacted more often when installed closer to the travel way edge, and are usually much longer than the shielded hazard. Thus, in order to reduce the frequency of severe guardrail crashes, an optimized length should be determined. Previously, the American Association of Highway and Transportation Officials Roadside Design Guide (RDG) suggested guardrail runout lengths which were dependent on posted speed limit and traffic volumes, but were considerably longer than those recommended in other studies assessing the optimal length-of-need (LON). Crash data analyses and simulation using the recently-updated Roadside Safety Analysis Program (RSAPv3) was conducted to evaluate the cost-effectiveness and estimated crash costs associated with different guardrail LONs. Crashes involving Kansas guardrail, which were compliant with recommendations provided in the 2006 AASHTO RDG, and occurring on freeways with divided medians were analyzed. The frequency, rate, and risk of shielded hazard crashes were extremely low. RSAPv3 analysis indicated that there was both an economic and safety benefit to reducing the installed LON, as well as utilizing different runout lengths for left- and right-side departures for divided roadways.


Highway Safety, Guardrail, Length-of-Need, RSAP, Benefit-to-Cost Analysis

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