United States Department of Transportation
i
Regionalized Safety Performance Functions
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2016-01-08
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[PDF-4.44 MB]
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TRIS Online Accession Number:01590519
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Edition:Final Report
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Abstract:The objectives of this project were to develop Pennsylvania-specific, regionalized safety performance functions (SPFs) that are consistent in functional form with the American Association of State Highway and Transportation Officials’ Highway Safety Manual. Regionalized SPFs for three roadway classes are included in this project: (1) rural two-lane highways segments and intersections; (2) rural multilane highway segments and intersections; and (3) Urban and suburban arterial (non-freeway) segments and intersections. For each of these roadway classes, the regionalized SPFs were developed to predict total crash frequency and the frequency of fatal + injury crashes on roadway segments and common intersection types of state-owned roadways. The regionalized SPFs were designed to capture any differences in safety performance across different geographic regions in Pennsylvania. The regionalization effort considered SPFs at the county, planning organization (metropolitan and rural), and engineering district levels. The results showed that, when an adequate sample of roadway segments or intersections were available for statistical modeling, district-level SPFs, with county adjustment factors, outperformed other regional or statewide models based on the predictive power of the models. When an adequate sample size was not available to estimate regionalized SPFs, statewide models, with district-level adjustment factors, were recommended to account for geographic differences in the Commonwealth of Pennsylvania. The results underscore the importance of estimating local SPFs if crash and roadway inventory data are available.
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