A Study on Surrogate Safety Measures at Unsignalized Intersection Blackspots in a Mixed Traffic Scenario

Vehicular movement and driver behavior at unsignalized intersections are responsible for increasing the susceptibility to potential crashes. Among them, unsignalized blackspots need serious attention because they have records of several crashes occurring. At intersections, right-turning vehicles from major and minor roads take risky actions and undergo serious conflicts with high-speed through-moving vehicles. So, the study proposed crash severity levels intending to predict the chances of crashes at unsignalized intersection blackspots for crossing and rear-end conflicts using estimated surrogate safety measures (SSM), i.e., postencroachment time (PET) and modified time to collision (MTTC), along with indicators like critical speed and time to stop (Ts). The study also focused on determining the percentage of critical conflicts and vehicle combinations for crossing and rear-end conflicts. To achieve the outcomes of the study, video data and crash data from four unsignalized intersection blackspots (three-legged and four-legged) from Nagpur, India, were collected. The PET values were determined for right-turning and crossing conflicts, and MTTC values were used for rear-end conflicts. Based on the threshold values of these SSM parameters, a range of crash severity values was proposed using the $k$-mean clustering analysis method. The severity level was divided into four levels, from A being the most severe to D having the least severe values, indicating that drivers have less than 1 s to react to a situation of conflict. From the study, it was observed that the percentage of critical conflicts was between 20.67% and 35.22% for crossing conflicts and 66.67% to 89.47% for rear-end conflicts. The vehicle combinations of two wheelers–two wheelers (2W–2W), two wheelers–light motorized vehicles (2W–LMV), and two wheelers–three wheelers (2W–3W) were found to be critical for crossing conflicts, and for rear-end conflicts, 2W–2W, LMV–2W, and LMV–LMV were critical.