Improving Safety for RITI Communities in Idaho: Documenting Crash Rates and Possible Intervention Measures

Abstract

This report describes a new set of Geographic Information System (GIS) tools that we created to conduct safety analyses. These new GIS tools can be used by state DOTs and transportation agencies to document crash rates and prioritize safety improvement projects. The tools perform Network Segment Screening, the first step in the Roadway Safety Management Process (RSMP) outlined in the Highway Safety Manual (HSM). After developing these new tools, we conducted two case studies to demonstrate how they can be used. The first case study was for screening intersections. Our analysis included all intersections on the Idaho State Highway System. In practice, the analysis would likely be done only for a subset of intersections, such as only for signalized intersections on urban arterials. We chose all intersections for illustration purposes. The result was a ranking of intersections that would most likely benefit from safety improvement efforts. We applied three performance measures to rank the intersections: Crash Frequency, Crash Rate, and Equivalent Cost. The second case study was for screening roadway segments. Again, the entire Idaho State Highway System was included for illustration. The HSM describes two key methods for screening roadway segments: Simple Ranking and Sliding Window. Both methods are available in the new tools. This case study demonstrates the advantage of the Sliding Window, which would be impractical to accomplish on a large scale without the assistance of our new GIS tools. The final part of the work presented in this report is a synthesis to identify and document possible measures to reduce crashes for RITI communities in Idaho and throughout the northwest region.