Advancing the Methodology for Identifying Crash Contributing Factors in Implementing a Systemic Approach for Prioritizing Sites for Safety Improvements

The traditional approach of network screening to identify roadway sites for safety improvements has issues, such as the tendency for safety countermeasures to be targeted only at locations that have experienced a high frequency of crashes. The systemic safety approach, on the other hand, proactively identifies risk factors for focus crash and site types, then reviews the road network and identifies locations for implementation of appropriate countermeasures based on the prevalence of these risk factors. Using crash data from Ohio collector road segments, the focus site type, as a case study, this research aimed to advance the systemic approach methodology by first developing a severity index (SI) that considers the frequency and cost of crashes in each severity level. An advanced method that integrates eXtreme Gradient Boosting (XGBoost) and SHapley Additive exPlanations (SHAP) algorithms was then proposed and applied to identify contributing factors to focus crash types by determining those affecting SI for a focus site type. The technique produced relative importance scores that were then used to rank and compare contributing factors for the focus crash types. Then, road segments were not only identified, but also prioritized for safety improvements targeting the focus crash type based on the prevalence of critical contributing factors and their importance scores. The example demonstrated that locations without crashes may still be categorized high priority for safety improvement with the systemic safety approach. The proposed methodology incorporates advanced concepts but is nevertheless implementable beyond the research community.