Safety Performance Assessment of Freeway Interchanges, Ramps, and Ramp Terminals

As part of the continuing efforts of the Ministry of Transportation Ontario to establish a technologically advanced knowledge base on the interaction of human factors, highway design and highway safety that can be put into practical use, the Ministry has undertaken the task of developing new safety performance functions for interchanges, ramps and ramp terminals for Ontario freeways. This new technology was created through the collection of data by using negative binomial regression modeling that relates collision frequency to traffic volumes and basic entity characteristics. This paper also presents the application of these safety performance functions for network screening using two varieties of the potential for safety improvement (PSI) index method, one based on expected collision frequency and one based on expected collision frequency in excess of what is considered normal.