The Development of Conflict Index for the Safety Assessment of Intersections Considering Crash Probability and Severity

The use of crash data based methodologies for safety evaluation has been usually problematic due to the many shortcomings such as, unavailability and low quality of historical crash data. Other than crash data based analysis, development of micro-simulation models in conjunction with surrogate safety measures is shown to have potential to complement traditional safety analysis. However several previous works found that existing measures for the assessment of intersection safety such as post-encroachment time (PET), time to collision (TTC) and speed cannot each one alone represent the overall safety levels including crash probability and severity simultaneously. Thus, this study aims to propose a safety measure that considers crash probability as well as expected severity. By utilizing the change in the total kinetic energy before and after the collision, angle of collision and PET, the proposed conflict index is derived. Several videotaped signalized intersections in Nagoya City, Japan are utilized to extract vehicle trajectories through which conflict characteristics are estimated. The relationship between the estimated distributions of the proposed index and the records of severe crashes of the same sites are presented. It is concluded that the proposed safety measure is successful in providing a similar ranking of different signalized intersection to the ranking which is based on the number of crashes occurred at each site. The proposed measure can assess policy makers in prioritizing different sites for safety improvements projects. (C) 2014 The Authors. Published by Elsevier B.V.