Safety Analysis of Interchanges

As the U.S. freeway system ages and becomes more congested, many parts of the system, particularly interchanges, need reconstruction or rehabilitation. In addition, new development and expanding urbanization often require new interchanges to be constructed along existing freeways. Because interchange projects are typically among highway agencies’ highest-cost projects, it is important that they be planned wisely. Improved safety should be a key justification for interchange improvement projects, but engineers lack a suitable tool for examining the safety performance of existing interchanges and anticipating the safety performance of new or rebuilt interchanges. The objectives of this research are to synthesize the current state of knowledge concerning the safety assessment of interchanges, develop a spreadsheet-based computational tool for performing safety assessments of interchanges, and identify gaps in knowledge concerning interchange safety assessment and future research needed to fill those gaps. This paper summarizes safety data related to interchanges, discusses the use of safety performance functions within the Interchange Safety Analysis Tool (ISAT) (the spreadsheet-based tool developed in this research), describes the scope and capabilities of ISAT, and identifies substantive gaps in the current state of knowledge that limit the ability of ISAT to provide all of the capabilities desired by potential users.