Systemic Low-Cost Countermeasures for an Unsignalized Intersection Safety Improvement Plan for Virginia

With more than 80,000 unsignalized intersections in Virginia, determining how and where to focus limited highway safety resources through deployment of low-cost, high-benefit systemic countermeasures is paramount to beginning to reduce the number of fatal and injury crashes at unsignalized intersections in Virginia. The purpose of this study was to develop a safety improvement plan for unsignalized intersections using systemic low-cost countermeasures. The scope of the study focused on unsignalized intersections with stop sign control on the minor approaches. Virginia’s unsignalized intersection crashes over a 5-year period were assessed to determine predominant crash trends and crash types to target for treatment. Three Virginia Department of Transportation (VDOT) databases (crashes, roadway inventory, and traffic counts) were combined for unsignalized intersections. Four focus collision types with the highest frequency of crashes and the greatest potential reduction in crashes were identified from the data: 3-leg angle, 3-leg fixed object off road, 4-leg angle, and 4-leg rear-end. Chi-square automatic interaction detection (CHAID) was used to perform a systemic analysis to identify a group of intersections based on independent variables (roadway inventory and traffic count variables) that were most strongly related to the focus collision types. After the crash assessment was performed, case studies of selected intersections in each group were reviewed to assess the factors that might influence the four focus collision types. A tiered list of countermeasures to deploy was developed based on the literature and input from VDOT staff. The countermeasures were intended to warn of the stop ahead, to make the stop sign and stop location more visible on the minor street, and to warn of the intersection ahead on the major street. The potential for safety improvement measure was used to prioritize the candidate treatment intersections. Before deployment, a study of the intersections conducted by district traffic engineering staff is planned in order to finalize the safety improvement plan. The output of the study is a safety improvement plan to deploy treatments to unsignalized intersections systemically as part of the safety program. The plan can be adjusted based on available funding.