Speed adjustment across freeway work zones under multiple feedback systems

OBJECTIVE: Work zones (WZs) are characterized by constrained roadway conditions and substantial variation in driving speed behavior. This study aims to investigate driver speed-adjustment behavior within a long freeway WZ, focusing on how speeds evolve across upstream and downstream segments under different speed-feedback mechanisms and traffic conditions. METHODS: High-resolution vehicle observations derived from video-based trajectory extraction were aggregated and analyzed to examine speed-adjustment behavior. Speed and time headway distributions were analyzed to understand traffic flow characteristics and speed adjustment patterns. For the speed-adjustment analysis, vehicle speeds were aggregated into one-minute intervals by lane, vehicle type, feedback condition, day type, and weather. A Bayesian generalized additive model (BGAM) was used to examine the influence of traffic and environmental factors on speed change, allowing for flexible modeling of nonlinear relationships. RESULTS: All three feedback configurations were associated with greater downstream speed reduction than the no-feedback condition. Speed Wizard showed the strongest association, followed by the Dynamic Speed Feedback Sign and the combined Speed Wizard + Portable Changeable Message Sign condition. Speed adjustment was also associated with lane, vehicle type, day type, weather, and traffic volume. The results also reveal a nonlinear relationship between initial speed and subsequent speed change, with progressively greater downstream reduction observed at higher upstream speeds. CONCLUSIONS: Speed feedback configuration and prevailing traffic conditions were associated with meaningful differences in segment-level speed adjustment within the observed freeway WZ. The findings indicated that message configurations, lane-specific behavior, vehicle composition, and traffic conditions should be considered when deploying speed feedback systems.