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South Carolina Department of Transportation – South Carolina’s SC 61 Rural Road Safety Project

Publication Year: 2021


This purpose of this case study is to present an example application of the American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) to support a rural road corridor analysis. The South Carolina Department of Transportation (SCDOT) Rural Road Safety Program (RRSP) focuses on improving, “safety on SC’s rural roadways through engineering solutions identified to reduce the frequency of fatal and serious injury crashes occurring on these roadways” (South Carolina Department of Transportation 2020). SCDOT used HSM spreadsheets to apply HSM predictive methods from chapter 10, Rural Two-Lane, Two-Way Roads (AASHTO, 2010), to assess alternative designs. The spreadsheets allowed SCDOT to apply an Empirical-Bayes (EB) analysis that compared the observed crash frequency with the expected crash frequency based on the corridor’s characteristics. Context and the preference of the public and local stakeholders were the governing challenges of this analysis. The historical context, Scenic Byway designation, and other natural barriers required SCDOT to consider numerous, slightly different alternatives. The goal, as well as the key challenge of the public engagement, was to present the HSM analysis as clearly and concisely as possible. The general public appreciated seeing the differences in crash prediction associated with changes to the cross-section relative to the “No-Build” option, and it demonstrated that SCDOT had taken the time to consider stakeholder input. This helped make the case that the surrounding landscape should be gently modified to improve safety.

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