An Innovative Approach to Assessing the Relative Risk at Rural Curved-Tangential Intersections


Mr. Alexandre Nolet - Alexandre is a Transportation Safety Engineer and Vice-Present of True North Safety Group. He has over twelve years of experience in the transportation consulting industry where his focus has been on road safety, collision analysis, traffic operations, and risk management. Alexandre has been involved in several road safety audits and in-service road safety reviews for various road jurisdictions throughout Canada. He is currently the president of CARSP.

Title of Abstract

An Innovative Approach to Assessing the Relative Risk at Rural Curved-Tangential Intersections


Due to lower traffic volumes and exposure, rural road networks create a specific challenge for road authorities to identify safety deficiencies and hazardous conditions through typical collision frequency reviews and network screening efforts. Curved-tangential intersections (“county curves”), are common in rural areas of North America and are legacy infrastructure at which a standard intersection between two roadways has been joined by a curve to facilitate a “heavier” and high speed through movement. They generally exist in lower density areas, with low entering volumes, and have limited collision history. Curved-tangential intersections typically consist of two severely skewed intersections at either end of a curve which create some unusual right-of-way assignments and turning movements with restricted visibility.


Given the lack of collision history and the unique nature of these intersections, the Region of Durham required an innovative approach to capture and rank the relative collision risk and severity of their 22 curved-tangential intersections, and to select appropriate remedial actions that were a function of the level of risk.


The Analytic Hierarchy Process (AHP) was chosen as the preferred method to allocate a relative weight to specific design, operational and safety criterion at each location, calculate a safety index, and create a priority ranking. AHP is a multi-criteria decision-making method and, in this study, was used to establish relative-risk comparisons between diverse intersection attributes such as geometry, operating speeds, traffic operations, collision history, visibility, and traffic control device application. In parallel, a North American industry scan was conducted to gain a better understanding of the safety issues experienced at similar intersections and to determine a suite of potential remedial actions. The recommended action plan primarily focused on addressing the visibility issues at the intersections, ranging from clearing obstructions at key conflict points to realigning the minor roadways to connect perpendicularly to the major roadways, with geometric changes proposed at locations with a higher risk index.


A range of remedial measures was identified to address many of the common deficiencies and potential safety issues identified at the study locations. Remedial measures were categorized into three categories: short-term, long-term, and potential improvement options.
Short-term actions included relatively inexpensive measures that could be implemented in the short-term for compliance with the guidelines, manuals, and best practices, without physical changes to the layout of the intersection, and that could be funded from operational or maintenance budgets. Long-term recommendations were more costly, which require long-term planning, design, property, and/or public consultation. Potential improvement options represented a subset of longer-term countermeasures that could be implemented at specific locations but are not currently required for implementation based on the safety performance and lower collision risk.


Moving forward, it is recommended to implement the short-term treatments at the skewed intersections, monitor the safety and operational changes at each location after the improvements, and consider long-term treatment if the observed safety issues are not resolved.


The approach developed can be applied by other jurisdictions to effectively compare the safety risk at lower volume/collision sites or within specific user/location subsets such as pedestrians, bicycles, trucks, school crossings, at-grade railway crossings, etc.