The unique configurations of the freeway interchanges around the region make it difficult to analyze them. They contain some characteristics of both the interstates and intersections, while also having very unique characteristics. For these reasons, the interchanges were analyzed independently from the other analyses.
For this analysis, all crashes included within the interchange were included. This includes crashes that occurred between the entrance and exit ramps on both the interstate and the arterial, within 150 feet of the centerlines of the respective roadways. It also includes an additional 350 foot buffer, for a total of a 500 foot buffer, at the end of each ramp along the interstate legs. This additional buffer was added to account for the abundance of crashes that occurred at locations where merging occurs.
Interchanges were assessed in a similar fashion as the intersections. They were ranked based on three factors:· Crash Frequency: the number of crashes that occurred at the interchange
· Crash Rate: the number of crashes that occurred per million vehicles entering an interchange
· Crash Severity Index: An index that assigns higher weights to crashes that result in injuries and fatalities than to crashes that result in property damage only