On the quantification of the spatiotemporal impact of a single discretionary lane change on upstream traffic safety and efficiency

Lane-changing is a critical driving maneuver, and understanding its effects on traffic safety and efficiency is essential for effective traffic management and optimization. However, existing studies provide limited means to account for natural traffic dynamics when identifying disturbances associated with lane changes. Moreover, methods for measuring the spatial extent and duration of the impact of a single discretionary lane change, as well as comprehensive metrics for quantifying its overall spatiotemporal impact, remain underdeveloped. To address these gaps, this study proposes a comprehensive analytical framework to evaluate the spatiotemporal impact of a single discretionary lane change on upstream traffic. The framework identifies affected following vehicles and their impact durations from vehicle trajectories before and after the lane change. A Travel Distance Bias indicator is introduced to measure the motion deviation of following vehicles relative to local reference vehicles, while vehicle-specific pre-event fluctuation envelopes and run-length persistence filters are used to reduce the misattribution of background traffic fluctuations to the lane-change event. Based on the affected vehicles and affected intervals, two aggregate indicators, the Total Efficiency Impact Magnitude (TEIM) and the Total Safety Impact Magnitude (TSIM), are developed to quantify efficiency- and safety-related impact magnitudes. Matched no-lane-change controls and method-comparison experiments provide comparative evidence that the affected-vehicle identification procedure reduces, but does not eliminate, false-positive detections caused by background traffic fluctuations. Empirical results based on Zen traffic trajectory data from Japan show that the identified impact in the target lane lasts on average 23.8 s, affects approximately 5.6 vehicles, and yields average TEIM and TSIM values of -10.8 m and 4.6%, respectively, corresponding to average efficiency loss and increased TTC-based unsafe exposure. In the original lane, the identified impact persists for about 25 s, affects 5.3 vehicles, and yields average TEIM and TSIM values of 4.7 m and 2.1%, respectively, corresponding to average efficiency gain and increased TTC-based unsafe exposure.