United States Department of Transportation
i
Analysis of FARS data on state highways in Oklahoma.
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2012-11-01
[PDF-1.62 MB]
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Abstract:Analysis of fatality automobile accident data can be challenging in rural areas where a relatively small number of
such accidents occurs on specific sections of highways. Combining crash data for 1998 to 2011 from the Fatality
Analysis Reporting System (FARS) and highway networks and design specifications from the Oklahoma
Department of Transportation (ODOT), this project employs Poisson regression analysis to determine what
roadway characteristics (e.g., grade, geometry, and design) are most associated with fatal crashes on
predominantly rural segments of highways in Oklahoma.
A state-wide model found that median width and type, terrain type, surface type and thickness, grade, and outside
shoulder width were all significant predictors of fatality crashes. Vertical grade was the most significant variable in
the state model, with uphill grades contributing to significantly more fatal crashes while flat roads modestly reduce
the risk. Terrain type was also very significant, both flat and rolling terrain categories having higher contributions to
fatality crash rates than baseline levels in residential areas. Outside shoulder width significantly negatively
correlated with fatalities, as wider shoulders mean more room for drivers to recover or at least shed speed.
Median width was also significant with the expected negative sign as wider medians result in fewer fatalities.
Surprisingly, median type was only moderately significant, though as expected most other median types did
contribute to higher crash rates compared to cable barriers.
The results provide information about what combinations of highway design traits have contributed most to past
crashes and therefore can identify potentially dangerous road segments system-wide. This information will help
transportation engineers evaluate current construction practice and seek ways to address design issues that are
shown to contribute significantly to serious crashes.
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