Iowa Department of TransportationSeveral layers were examined as part of the highway improvement needs and risk analysis conducted for the 2022 State Transportation Plan. Identifying safety risk for the primary highway systems was analyzed through the use of Safety Performance Functions (SPFs) and the subsequent output of Potential for Crash Reduction (PCR). An SPF is an equation used to predict the average number of crashes per year at a location as a function of exposure and, in some cases, roadway or intersection characteristics. Generally, SPFs more realistically demonstrate the relationship between crashes and traffic volume. SPFs account for the regression to the mean by using an Empirical Bayes statistical method. The advantages of using this method are more accurately calculating the potential for safety improvement and acknowledging the complex, non-linear relationship between crash frequency and volume. For any given segment, the potential for crash reduction (PCR) can be determined by evaluating the predicted number of crashes for the location based on volume. This is based on the functional form of the SPF. The predicted number of crashes for a given site is adjusted by the Empirical Bayes method which adjusts the prediction based on the observed crashes at a site. The difference between the corrected number of crashes with the Empirical Bayes and the predicted number of crashes based on the SPF is considered PCR.For the State Long-Range Transportation Plan SLRTP ten different SPF models (and 29 sub models) based on roadway characteristics were developed to evaluate and predict the number of crashes on Iowa's primary highways. Subsequently, PCR values were calculated for each segment. The results were aggregated to the defined primary highway corridors established by the Systems Planning Bureau. In evaluating safety risk for the purposes of the SLRTP we normalized the PCR per year by the segment or corridors length.Note: this dataset supersedes SCOPING_MOBILITY_AND_SAFETY_RETIRED, effective with the publication of the State Long Range Transportation Plan (SLRTP) and Freight Plan update in 2022.ArcGIS FeatureLayerhttps://hub.arcgis.com/datasets/91c7006158f341c7a966bec689832c23_0engIowaDOT Open DataPublicScoping PCR Safety [Iowa]Web servicesIowaLast Modified: 2026-01-08