Improvements to Road Safety Improvement Selection Procedures for Connecticut

Estimating and applying safety performance functions (SPFs), or models for predicting expected crash counts, for roads under local jurisdiction is often challenging due to the lack of vehicle count data to be used for exposure, which is a critical variable in such functions. This report describes estimation of SPFs for local road intersections and segments in Connecticut using socio-economic and network topological data instead of traffic counts as exposure. SPFs are developed at the traffic analysis zone (TAZ) level, where the TAZs are categorized into six homogeneous clusters based on land cover intensities and population density. SPFs were estimated for each cluster to predict the number of intersection and segment crashes occurring in each TAZ. One aggregate SPF using the entire dataset was also estimated to compare with the individual cluster SPFs. The number of intersections and the total local roadway length were also used as exposure in the intersection and segment SPFs, respectively. Total population, retail and non-retail employment and average household income are found to be significant variables. Ten percent of the observed data points were reserved for out of sample testing and in all cases, these out of sample predictions were as good as the in sample predictions. The SPFs are applied in two Connecticut towns to illustrate the usefulness of the SPFs as a network screening tool.