Pedestrian, Crowd, and Evacuation Dynamics

This contribution describes efforts to model the behavior of individual pedestrians and their interactions in crowds, which generate certain kinds of self-organized patterns of motion. Moreover, this article focusses on the dynamics of crowds in panic or evacuation situations, methods to optimize building designs for egress, and factors potentially causing the breakdown of orderly motion.Comment: This is a review paper. For related work see http://www.soms.ethz.c

Traffic and Related Self-Driven Many-Particle Systems

Since the subject of traffic dynamics has captured the interest of physicists, many astonishing effects have been revealed and explained. Some of the questions now understood are the following: Why are vehicles sometimes stopped by so-called ``phantom traffic jams'', although they all like to drive fast? What are the mechanisms behind stop-and-go traffic? Why are there several different kinds of congestion, and how are they related? Why do most traffic jams occur considerably before the road capacity is reached? Can a temporary reduction of the traffic volume cause a lasting traffic jam? Under which conditions can speed limits speed up traffic? Why do pedestrians moving in opposite directions normally organize in lanes, while similar systems are ``freezing by heating''? Why do self-organizing systems tend to reach an optimal state? Why do panicking pedestrians produce dangerous deadlocks? All these questions have been answered by applying and extending methods from statistical physics and non-linear dynamics to self-driven many-particle systems. This review article on traffic introduces (i) empirically data, facts, and observations, (ii) the main approaches to pedestrian, highway, and city traffic, (iii) microscopic (particle-based), mesoscopic (gas-kinetic), and macroscopic (fluid-dynamic) models. Attention is also paid to the formulation of a micro-macro link, to aspects of universality, and to other unifying concepts like a general modelling framework for self-driven many-particle systems, including spin systems. Subjects such as the optimization of traffic flows and relations to biological or socio-economic systems such as bacterial colonies, flocks of birds, panics, and stock market dynamics are discussed as well.Comment: A shortened version of this article will appear in Reviews of Modern Physics, an extended one as a book. The 63 figures were omitted because of storage capacity. For related work see http://www.helbing.org

Meander dynamics: A nonlinear model without curvature restrictions for flow in open?channel bends

Despite the rapid evolution of computational power, simulation of meander dynamics by means of reduced and computationally less expensive models remains practically relevant for investigation of large?scale and long?term processes, probabilistic predictions, or rapid assessments. Existing meander models are invariantly based on the assumptions of mild curvature and slow curvature variations and fail to explain processes in the high?curvature range. This article proposes a nonlinear model for meander hydrodynamics without curvature restrictions. It provides the distribution of the main flow, the magnitude of the secondary flow, the direction of the bed shear stress, and the curvature?induced additional energy losses. It encompasses existing mild curvature models, remains valid for straight flow, and agrees satisfactorily with experimental data from laboratory experiments under conditions that are more demanding than sharp natural river bends. The proposed model reveals the mechanisms that drive the velocity redistribution in meander bends and their dependence on the river's roughness Cf, the flow depth H, the radius of curvature R, the width B, and bathymetric variations. It identifies Cf?1H/R as the major control parameter for meander hydrodynamics in general and the relative curvature R/B for sharp curvature effects. Both parameters are small in mildly curved bends but O(1) in sharply curved bends, resulting in significant differences in the flow dynamics. Streamwise curvature variations are negligible in mildly curved bends, but they are the major mechanisms for velocity redistribution in sharp bends. Nonlinear feedback between the main and secondary flow also plays a dominant role in sharp bends: it increases energy losses and reduces the secondary flow, the transverse bed slope, and the velocity redistribution.Hydraulic EngineeringCivil Engineering and Geoscience

Impact scales of fluvial response to management along the Sacramento River, California, USA: transience versus persistence

Most large rivers in industrialized nations are managed carefully to maximize their benefits (e.g., water supply, hydroelectricity), while limiting their hazards (e.g., floods). Management strategies employed in lowland river systems such as large dams, levees, and bypasses affect flow regimes, sediment supply to channels, and the net flux of sediment through river reaches fairly soon after construction. Therefore, equilibrium approaches to fluvial geomorphology are typically inadequate to characterize the effects of anthropogenic activity on management timescales (10–102 years). Each human alteration to the fluvial system has an ‘impact scale’ in time and space, and these impacts may manifest as persistent (steady, localized influence) or transient (dying away with distance and/or time) landscape responses. The cumulative effects of transient and persistent fluvial responses influence flood risk, the state of aquatic and riparian habitat, and the fate and transport of contaminants. Whereas some persistent impacts are straightforward to anticipate (e.g., reduced flood peaks), transient impacts may result from emergent behavior in fluvial systems and are not easily predicted. This chapter outlines the differences between these divergent landscape responses to perturbations in managed fluvial systems using examples from the Sacramento River in California. The discussion focuses on: (1) persistent local signals of altered flow regimes below large dams that attenuate in lowland valleys, (2) transient longitudinal sediment redistribution due to changes in sediment supply by dams, (3) transience in the magnitude and frequency of flow over flood control weirs into flood bypasses, and (4) persistent overbank sedimentation in localities that favor the export of sediment from channels to floodplains. The chapter shows that persistent and transient fluvial processes coexist and interact in large, lowland river basins subject to anthropogenic perturbations in a manner that can produce unanticipated outcomes that are relevant to aquatic and riparian ecosystems, river management, as well as to human communities living in lowland floodplains. It suggests the need for more careful examination of the impact scales of river management to clarify trajectories of landform evolution