An analysis of the interactions between vehicle groups at intersections under mixed traffic flow conditions

Grouping behavior is a unique characteristic of mixed traffic dominated by motorcycles. At 2-phased signalized and non-signalized intersections in Hanoi, there are increasingly serious conflicts between vehicles groups, especially between the unprotected left-turn and straight-go groups, thereby reducing traffic speeds and increasing accidents. This study aimed to investigate the mechanisms of the inter-group interactions and suggest measures to manage the intersections. First, a general analysis was conducted to initially understand the interactive strategies by each group and determinant factors. Then, a gap acceptance model was developed to deeply analyze the gap decisionmaking process by the left-turn groups and capture behavioral differences between the motorcyclists and car drivers who lead the groups. The study found that the total gap, combining the longitudinal and lateral gaps, strongly influenced the gap decision of both the drivers. Interestingly, the number of motorcycles in the left-turn group could make its leading motorcyclists more aggressive. The leading car drivers appeared to be sensitive to the expected waiting time while the motorcyclists did not.