Abstract
Our statistical analysis of accident records on expressway in past five years showed that two different kinds of accidents (i.e. side-by-side collision and rear-end-collision) occurred at accident-prone toll barriers (TBs). Besides, as a safety indicator for conflict risk assessment, TTC (Time-To-Collision) is widely used. However, since TTC regards size of each vehicle as a single dot to simplify calculation, identifying types of conflict is difficult. Therefore, in this study, we propose new safety indicator 2-D TTC for identifying types of conflict by considering size information of each vehicle when calculating TTC. To know detailed information about traffic conflicts on TBs, we analyzed 845 vehicle trajectories on an accident-prone TB and assessed traffic conflict risk among vehicles at the TB using 2-D TTC. As a result, we detected 11 near-miss conflicts; among them, 5 conflicts are judged as side-by-side collision risk, and 6 conflicts are judged as rear-end-collision risk. This result shows that two different kinds of conflict risk could simultaneously increase at TBs.
