United States Department of Transportation
i
Highway Safety Manual Part D: Validation and Application in Wyoming
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2019-05-01
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[PDF-2.44 MB]
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Edition:Final report
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Abstract:This study is considered a first step toward validating applicability of the Highway Safety Manual (HSM) Part D to Wyoming conditions. The HSM Part D provides a quantitative measure of safety for various countermeasures known as crash modification factors (CMF). These CMFs are provided for four distinct groups of treatments: roadway segments (e.g., rumble strips, passing lanes, etc.), intersections (e.g., flashing yellow arrows), special facilities (e.g., Highway-rail crossings, and interchanges), and road networks. CMFs provided in the HSM Part D are calibrated based on data collected from a few states in the United States, which may not represent the same safety efficacy of countermeasures implemented in Wyoming. The objectives of this study are to (1) validate applicability of the HSM Part D to Wyoming conditions, (2) calibrate CMFs for various countermeasures in Wyoming, and (3) provide recommendations in terms of data requirements, how to mitigate data shortcoming, and applicability of alternative analytical methodologies to evaluate the safety effectiveness of specific countermeasures. Depending on data availability, various observational before-after and cross-sectional techniques were adopted in this study to calibrate CMFs for six countermeasures applied to roadway segments, intersections, and special facilities. Results indicated that the majority of these countermeasures are statistically significant in reducing crash frequency and severity. Moreover, CMFs from the HSM and Clearinghouse should not be implemented in Wyoming without proper calibration and validation. Wyoming conditions are unique and therefore, site-specific Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) must be calibrated and updated every five years.
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