A Comprehensive Framework of Traffic Shockwave Propagation

Traffic congestion on the freeways generally propagates in the form of traffic shockwaves. While properties of traffic shockwaves have been widely examined, there lacks a unified framework that explains all processes traffic shockwaves undergo. In addition, their lateral propagation mechanisms across lanes is not widely known. In this paper, we propose a comprehensive duration-based framework that stochastically captures seven shockwave propagation processes: emergence, absorption, merging, splitting, longitudinal propagation, recurrence, and lateral propagation. This framework contains a longitudinal model that jointly captures the duration of shockwaves and the change in the surrounding traffic states, and a lateral model that captures the recurrence and lateral propagation processes that cause emergence of new shockwaves. By designing an algorithm to extract traffic shockwaves from Third Generation Simulation (TGSIM) Dataset and Next Generation Simulation (NGSIM) Dataset and fitting them with our models, we find strong interconnection between four variables: the shockwave propagation velocity, the average vehicle speed, the standard deviation of vehicle speed, and average vehicle acceleration. In addition, shockwave propagation velocity may influence the likelihood of shockwave splitting. Furthermore, we find that the emergence of traffic shockwaves is likely caused by lateral propagation from the adjacent lanes, whose direction tends to be consistent to that of lane changes (LCs). However, the model results also suggest differences in the lateral propagation mechanisms of shockwaves between TGSIM and NGSIM datasets, highlighting potential dependencies on roadway geometry and the location and time period of data collection and indicating that shockwave propagation is subject to substantial uncertainty captured through stochastic hazard probabilities.