United States Department of Transportation
i
Validation and application of highway safety manual (part D) in Florida.
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2014-03-01
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[PDF-3.74 MB]
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Abstract:The Highway Safety Manual (HSM) Part D provides a comprehensive list of the effects of safety
treatments (countermeasures). These effects are quantified by crash modification factors (CMF), which are based
on compilation from past studies of the effects of various safety treatments. The HSM Part D provides CMFs for
treatments applied to roadway segments (e.g., roadside elements, alignment, signs, rumble strips, etc.),
intersections (e.g., control), interchanges, special facilities (e.g., highway-rail crossings), and road networks.
Thus, an assessment of the applicability of the HSM in Florida is essential. The objectives of this study are (1) to
develop CMFs for various treatments in Florida for the same setting (rural/urban), road type, crash type, and
severity level, (2) to evaluate the difference between these Florida-specific CMFs and the CMFs in the HSM, and
(3) to recommend whether the CMFs in the HSM can be applied to Florida or new Florida-specific CMFs are
needed. Different methods of observational study – before-after (B-A) and cross-sectional (C-S) – were used to
calculate CMFs for a total of 17 treatments applied to roadway segments, intersections and special facilities. The
CMFs calculated using the before-after with comparison-group (C-G) and empirical Bayesian (EB) methods,
only the CMF with lower standard error was selected. The methods of calculating CMFs were determined based
on the availability of the data and the methods used in the HSM, if the CMFs were provided in the HSM. It was
found that Florida-specific CMFs were generally statistically significant, and safety effects represented by the
CMFs were intuitive, similar to the CMFs in the HSM. It was also found that Florida-specific CMFs for the
treatments not included in the HSM showed significant positive effects in reducing crash frequencies.
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