Traffic conflict characteristics and evolution mechanism in freeway weaving segments with varying spacing

With the rapid expansion of China's freeway network and the increasing density of interchange clusters, reduced interchange spacing has emerged as a critical challenge for weaving section safety. To systematically characterize how spacing affects the distribution, severity, and duration of traffic conflicts in weaving areas, this study collected aerial video data from four weaving sections with spacing of 400 m, 600 m, 850 m, and 1400 m along the Changhu Freeway in Dongguan. Using the Data From Sky video analysis platform for trajectory extraction and time-to-collision (TTC)-based surrogate safety analysis, the spatiotemporal evolution of traffic conflicts under varying spacing conditions was investigated. The research demonstrates that spacing is a critical factor influencing conflict risk. Reduced spacing exacerbates risk through spatial compression effects, manifested by a leftward shift of the primary TTC distribution peak, reduced collision avoidance time, and a significant increase in both the proportion of critical conflicts and TET duration. In contrast, longer spacing (850 m and 1400 m) provides necessary buffer space, optimizes conflict distribution, and reduces severity. The weaving flow ratio shows a positive correlation with the unit conflict rate. The 850 m scenario exhibits the highest conflict rate due to its combination of high traffic volume and high weaving flow ratio; however, conflict severity remains primarily regulated by spacing. Conflicts between heavy vehicles (L-L) present the highest risk, with a mean TTC of only 2.3 s and a critical conflict proportion of 18.53%, while light vehicle combinations (S-S) perform optimally. Vehicle movement intentions also significantly influence conflict characteristics: combinations with shared intentions (S-S, F-F, H-H) exhibit elevated risks due to high trajectory overlap, and their conflict numbers show an increasing trend under longer spacing. In contrast, heterogeneous vehicle combinations (S-F, S-H) are less affected by spacing variations. Based on these findings, a minimum spacing of 850 m is recommended as a practical safety threshold for weaving section design, and vehicle-type-specific management measures are advised for constrained sections below this benchmark. The findings of this study can provide a theoretical foundation and practical guidance for the planning, design, and management of weaving sections in freeway interchanges.