Vehicle operational characteristics and driving risks in short spacing weaving areas of ultra-high traffic volume expressways

To clarify the vehicle operation characteristics, traffic conflicts, and accident occurrence risks in the short spacing interchange weaving areas of ultra-high traffic volume expressways, the Dayouyuan-Songshanhu Interchange of Changping-Humen Expressway was selected as the research object. The vehicle driving data in the short spacing interchange weaving area were collected by unmanned aerial vehicles, and the precise tracking and identification of vehicle operation states were conducted in combination with the Data From Sky Viewer video analysis platform. A total of 1 883 vehicle trajectory data were obtained. From the dimensions of different lanes, the vehicle operation characteristics and diverging and merging vehicle lane-changing behavior characteristics in the short spacing weaving area under ultra-high traffic conditions were deeply analyzed, and the conflict distribution within the weaving area was obtained. The research results indicate that the speed characteristics between lanes present significant differences; the outer lane forms a reverse-trumpet acceleration pattern due to spacing compression (the average speed increases by 12.3%), and the speed bandwidth value at 200 m before its diverging nose surges by 23%; the auxiliary lane achieves efficiency optimization through the "acceleration and deceleration" two-stage strategy; the headway distribution has obvious lane differentiation, and the negative skewness distribution of the main lane is significant (the proportion of 0-80 m spacing is no less than 75%); the proportion of dangerous spacing in the inner lane reaches 61.1%, while the occurrence rate of dangerous spacing in the high-speed area of the auxiliary lane rises to 71.6%; the merging and diverging vehicles present differentiated lane-changing behaviors; the merging vehicles adopt short-distance lane-changing concentrated at 200 m after the nose point, while the diverging vehicles implement long-distance lane-changing, and the conflict severity is higher; the through-merging conflict becomes the main risk source due to the large speed difference. Based on the spatiotemporal dynamic characteristics, it is proposed that the lane-changing length in the diverging area should be no less than 500 m to mitigate the sudden braking risk, and the geometric parameters of the acceleration lane in the merging area should be mainly optimized, to ensure that the vehicle speed matches for safe merging. The theoretical basis and technical support are provided for the safety design of the short spacing weaving area.