United States Department of Transportation
i
Development of Speed Crash Modification Factors (CMFs) Using SHRP2 Roadway Information Database (RID), Volume II: Appendices
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2024-07-01
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[PDF-9.95 MB]
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Edition:Final Report
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Abstract:Speed is widely recognized as having significant safety impacts, especially on the severity of crashes. However, these effects are complex and generally have not been captured in the Highway Safety Manual (HSM) (American Association of State Highway and Transportation Officials (AASHTO) 2010). The current Federal Highway Administration (FHWA) project developed speed-related crash modification factors (CMFs) for 12 different roadway facility types—rural highways, urban and suburban arterials, and rural and urban freeways—by using Washington and North Carolina data from three major databases: Second Strategic Highway Research Program Roadway Information Database, National Performance Management Research Dataset, and Highway Safety Information System (VTTI 2020; Iowa State University of Science and Technology 2023; National Academies of Sciences 2023; RITIS 2023; FHWA n.d.). The results show that speed variation (e.g., operating speed standard deviation) was the dominant speed measure for rural highways and rural and urban freeways, and speed differential (i.e., difference between the posted speed limit and average operating speed) was the dominant speed measure for urban and suburban arterials. In most cases, the association of speed variation/differential with crashes is positive. The researchers developed CMFs for 129 crash types and severity levels, and most obtained three-star CMF Clearinghouse ratings (AASHTO 2010; FHWA 2023a). These CMFs were developed through a data-driven safety analysis approach, and application of these CMFs (e.g., in HSM-related evaluation tools) requires careful interpretation. The findings show that inclusion of speed-related CMFs improves model precision. While this study focused on Washington and North Carolina data, other States can use the documented approach to develop speed-related CMFs for their own jurisdictions. This volume is the second in a series. The other volume in the series is FHWA-HRT-24-129, Development of Speed Crash Modification Factors (CMFs) Using SHRP2 Roadway Information Database (RID): Volume Ⅰ: Final Report.
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