Evaluating Operational Safety of Through Streams Affected by Permitted Left-turning Vehicles

At a signalized intersection with a permitted phase, crossing through vehicles are always affected by permitted left-turning vehicles that compete for the priority. This paper utilizes the time headway data collected from through streams within the intersection and introduces a new index, the outlier rate to quantitatively describe the level of operational safety of through vehicles. An algorithm framework is developed to calculate the value of the outlier rate, including phase-space reconstruction module based on C-C method, Lyapunov stability analysis module based on the maximal Lyapunov exponent and outliers removing module by measuring the distance to the mean value. Leading on from that, case studies are conducted at four sites in Changchun, China. The results show significant difference of the operational safety of through streams between the permitted and the protected left-turning phase. The proposed method in this study provides traffic engineers with an accessible means of measuring the intersection safety and an effective reference in before-and-after evaluations.