Benefit–Cost-Based Method to Determine When Safety Performance Functions Should be Redeveloped for Use in Intersection Network Screening

Abstract

Network screening is the process of identifying the sites within the road network that are of highest priority for detailed safety audits and interventions. Contemporary road safety network screening methods rely on safety performance functions (SPFs), which are statistical models relating site characteristics to the number of crashes. SPFs are developed on the basis of historical crash and traffic volume data and should be periodically redeveloped to accurately reflect changes in the underlying relationships that result from changes in the network, traffic behavior, operational performance of vehicles, rules of the road, and other contributing factors. However, presently, there is no guidance available to practitioners to enable them to objectively decide when redevelopment of SPFs is warranted. In this study, we present a practical method to provide this guidance for network screening of intersections that reflects both the expected benefits of SPF redevelopment in relation to improved network screening accuracy and the cost of redevelopment. The data required for this method are either already available in municipalities which have locally developed SPFs or can be easily estimated. The estimation models for the method are created based on real data sets and were successfully tested on validation data sets.