Microscopic features of moving traffic jams

Kerner, Boris S.; Klenov, Sergey L.; Hiller, Andreas; Rehborn, Hubert · 2006 · OpenAlex-citations

DOI: 10.1103/physreve.73.046107

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Summary

This paper investigates the microscopic spatiotemporal structure of moving traffic jams, specifically distinguishing between "wide moving jams" and "synchronized flow" within the framework of three-phase traffic theory. The research is motivated by the need to understand the complex internal dynamics of congested traffic, particularly the phenomenon of "moving blanks" and flow interruptions that characterize wide moving jams. While macroscopic criteria define these phases, the microscopic mechanisms driving their formation and propagation had not been fully elucidated. The authors aim to identify empirical features of these structures and explain their physical origins through numerical simulations. The study employs a dual approach combining empirical analysis of single-vehicle data and microscopic traffic simulations. Empirical data were collected from induction loop detectors on two German freeways (A5-South and A92-West), allowing for the calculation of individual vehicle speeds, time headways, and flow rates. The authors define a microscopic criterion for wide moving jams based on "flow interruption," where the maximum time headway within the jam significantly exceeds the mean acceleration delay at the downstream front. Numerical simulations utilized microscopic models incorporating speed adaptation effects and driver time delays to replicate these empirical observations and explore the emergence of moving blanks and jam front structures. Key findings reveal that wide moving jams possess a complex internal structure consisting of alternating regions of flow interruption and low-speed states associated with "moving blanks." During flow interruption, vehicles come to a standstill, creating large space gaps that are subsequently covered by moving vehicles, resulting in blanks that propagate upstream against the flow. The study identifies that previous empirical studies suffered from systematic errors in density estimation because they used time-averaged flow rates rather than spatial density definitions during flow interruptions. Simulations demonstrate that moving blanks emerge primarily due to lane-changing behaviors at the upstream jam front, which disrupt vehicle platoons and create irregular spacing. Furthermore, the analysis of jam fronts shows that flow rates at the upstream front are higher than at the downstream front for the same density, due to shorter time headways during deceleration compared to acceleration. The significance of this work lies in providing a robust microscopic criterion to distinguish wide moving jams from synchronized flow, even using single-location data. It clarifies the physical nature of wide moving jams as distinct phases characterized by coherent downstream front velocity and internal flow interruptions. The findings also correct previous misunderstandings regarding flow-density relationships in congested traffic by highlighting the errors inherent in using time-averaged data during flow interruptions. By linking microscopic vehicle behaviors, such as lane changes and acceleration delays, to macroscopic traffic phases, the paper strengthens the theoretical foundation of three-phase traffic theory and offers insights for improving traffic flow models and congestion management strategies.

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• traffic density