Quantitative Characterization of Lane-Changing Urgency Under Route Constraint

This paper proposes a quantitative urgency coefficient that dynamically calibrates the acceptable lane-changing gap in the target-lane under route constraints. The coefficient is modeled as a function of remaining distance to the diverging point and embedded into the calculation of the time-to-collision (TTC) threshold relative to leading and following vehicles in the target lane. Using a trajectory dataset collected at a single urban expressway diverging area, lane-changing samples under route constraints with the accepted TTC observed at lane-changing initiation are extracted, and datasets are constructed across six traffic scenarios and four driver behavioral profiles for model calibration. Results show that urgency increases nonlinearly and monotonically as the remaining distance decreases, with pronounced growth under a low speed difference between the target lane and the current lane and a high target-lane density. Relative to the normal profile, the route-priority profile exhibits the earliest urgency onset, a steeper climb, and a moderate maximum urgency; the speed-priority profile exhibits a later onset but the steepest climb and the h3ghest maximum urgency; the comfort-priority profile exhibits an earlier onset, the most gradual climb, and the lowest maximum urgency. The proposed model may provide useful insights for dynamic adjustment of TTC thresholds in AV lane change.