Analysis of the Safety Influence Area for 4-Legged Signalized Intersections

It is common in crash data recording and safety studies to designate crashes occurring within a default radius from intersections as occurred at or influenced by intersections. The purpose of this study is to investigative how intersection attributes affect this safety influence area. Data for a sample of 177 four-legged signalized intersections was collected from the state of Florida. Based on the crash data and the approach features, the intersection inside area (from the center to the stop bar, used to designate "at intersection" crashes) and the safety influence area (measured upstream from the stop bar, used to designate "intersection-related" crashes) were explored using the classification trees method. Results show that the inside area is mainly influenced by the intersecting roadway; however, the approach upstream safety influence area is mainly affected by the attributes of that approach. The study also examined when the safety influence area extends beyond the physical functional area. Finally, test statistics show that intersection-related crashes defined by a 250 feet boundary versus varying boundaries are significantly different. The research concluded that it is better to define "at-intersection" and "intersection-related" safety influence areas for each approach separately and then based on approach features to determine their size.