A Roadway Context Classification Approach for Developing Safety Performance Functions and Determining Traffic Operational Effects for Florida Intersections

Abstract

This research developed safety performance functions (SPFs) based on a new Florida Department of Transportation (FDOT) context classification system which contains eight context categories as opposed to the three classifications used in the Highway Safety Manual (HSM). To develop these context-specific SPFs, data were collected for several potential predictor variables, including geometric, traffic, signalization, and other related intersection data based on the Model Inventory of Roadway Elements (MIRE) 2.0, allowing for standard data collection across agencies. Multiple modeling methodologies were utilized and compared to identify the best-performing models and develop a unique context-specific SPF for each intersection group. While some variables, such as major AADT, were common to multiple SPFs, each SPF contained a unique set of variables and different variable coefficients. These unique insights can help FDOT understand crash-influencing factors for different intersection types, identify intersections with high potential for crash reduction, and implement effective countermeasures. The individual group SPFs were also compared to HSM SPFs from the HSM and full context category SPFs. These comparisons showed the improved accuracy and additional insights provided by the individual context-specific SPFs. In addition, departments of transportation from across the United States were surveyed about their current SPF development practices and context classification. Many states (64% of the 42 respondents) use HSM SPFs or SPFs calibrated to their jurisdiction. Although 62% of states had not heard of context classification, 67% of states expressed interest in the system, emphasizing the importance of this research to improve intersection safety across the nation.