Estimating the safety performance function for urban unsignalized four-legged one-way intersections in Palermo, Italy

Starting from consideration that urban intersections are sites with promise for safety and operationalimprovements, the paper describes the steps taken to develop a crash predictive model forestimating the safety performance of urban unsignalized intersections located in Palermo, Italy.The focus is on unsignalized four-legged one-way intersections widespread in Italian downtowns.The sample considered in the study consist of 92 intersections in Palermo, Italy. For the study werecollected crashes occurred in the sites during the years 2006-2012, geometric design and functionalcharacteristics and traffi c fl ow. Results showed that data were overdispersed and NB1 distributed.In order to account for the correlation within responses Generalized Estimating Equations (GEE)were used under different working correlation matrices