The Types Division and Severity Threshold of Traffic Conflict on Freeway Interchange

This paper selects time to collision (TTC) as the traffic conflict index. Shooting high-definition video from high altitude above freeway interchange by unmanned aircraft, the TTC was calculated by processing software. The mechanism of traffic conflict on Freeway Interchange area was researched by combining subjective and objective method, and then defined severity. Firstly, conflict observers were trained. Twelve observers were trained repeatedly on the judgment of traffic conflict type and severity cognitive until a consensus was reached. Secondly, the subjective judgment on traffic conflict types and severity was made. The video clips containing traffic conflict were selected, and then all observers together determined the type of each conflict and severity. Thirdly, TTC samples were analyzed. The obviously unsuitable TTC samples were excluded, and the rest would be tested whether meet the sample size requirement of each type of traffic conflict. Finally, the TTC threshold value was defined. According to the cumulative frequency distribution of each type TTC, 85% value was selected as severity of traffic conflict threshold.