This Final Report documents the validation of urban and rural arterial safety performance functions (SPFs) developed for the Oregon Department of Transportation (ODOT) SPR 720 study titled Quantifying Safety Performance of Driveways on State Highways. For this previous effort, the research team determined that the crash reporting that indicated a driveway may have been involved in the crash was not a dependable variable, so they developed SPFs for all non-intersection-related arterial crashes (of which many were likely due to vehicle interactions at driveway locations). Due to a limited sample size in the original study, the Final Report for SPR 720 recommended sampling of additional study sites and validation of the original study models based on these new randomly sampled locations. The information in this report reviews the subsequent validation effort and the resulting recommendations. In general the original models performed very well in response to the validation tests. The research team evaluated spatial transferability, spatial-temporal transferability, and individual coefficient stability and significance. The urban model performed well with the spatial transferability resulting in statistically equivalent values, the spatial-temporal transferability providing similar values but not statistically equivalent at the 95 percent level, and all but one of the model variables (titled “Other DW”) determined to be statistically significant. The rural model also performed well as it was determined to provide statistically equivalent predictions for spatial transferability as well as for spatial-temporal transferability. In addition, the validation analysis for the individual coefficients found that only the “Four.Travel.Lanes” and the “Number.of.DW.Clusters” variables were not statistically equivalent at the 95 percent level. Ultimately, the research team developed enhanced models with the enriched data set so as to refine the original models and simplify their structure, where feasible. (Author/publisher)
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