22 research outputs found
DECENTRALIZED APPROACHES TO ADAPTIVE TRAFFIC CONTROL AND AN EXTENDED LEVEL OF SERVICE CONCEPT
Traffic systems are highly complex multi-component systems suffering from instabilities and non-linear dynamics, including chaos. This is caused by the non-linearity of interactions, delays, and fluctuations, which can trigger phenomena such as stop-and-go waves, noise-induced breakdowns, or slower-is-faster effects. The recently upcoming information and communication technologies (ICT) promise new solutions leading from the classical, centralized control to decentralized approaches in the sense of collective (swarm) intelligence and ad hoc networks. An interesting application field is adaptive, self-organized traffic control in urban road networks. We present control principles that allow one to reach a self-organized synchronization of traffic lights. Furthermore, vehicles will become automatic traffic state detection, data management, and communication centers when forming ad hoc networks through inter-vehicle communication (IVC). We discuss the mechanisms and the efficiency of message propagation on freeways by short-range communication. Our main focus is on future adaptive cruise control systems (ACC), which will not only increase the comfort and safety of car passengers, but also enhance the stability of traffic flows and the capacity of the road (“traffic assistance”). We present an automated driving strategy that adapts the operation mode of an ACC system to the autonomously detected, local traffic situation. The impact on the traffic dynamics is investigated by means of a multi-lane microscopic traffic simulation. The simulation scenarios illustrate the efficiency of the proposed driving strategy. Already an ACC equipment level of 10% improves the traffic flow quality and reduces the travel times for the drivers drastically due to delaying or preventing a breakdown of the traffic flow. For the evaluation of the resulting traffic quality, we have recently developed an extended level of service concept (ELOS). We demonstrate our concept on the basis of travel times as the most important variable for a user-oriented quality of service
Self-Control of Traffic Lights and Vehicle Flows in Urban Road Networks
Based on fluid-dynamic and many-particle (car-following) simulations of
traffic flows in (urban) networks, we study the problem of coordinating
incompatible traffic flows at intersections. Inspired by the observation of
self-organized oscillations of pedestrian flows at bottlenecks [D. Helbing and
P. Moln\'ar, Phys. Eev. E 51 (1995) 4282--4286], we propose a self-organization
approach to traffic light control. The problem can be treated as multi-agent
problem with interactions between vehicles and traffic lights. Specifically,
our approach assumes a priority-based control of traffic lights by the vehicle
flows themselves, taking into account short-sighted anticipation of vehicle
flows and platoons. The considered local interactions lead to emergent
coordination patterns such as ``green waves'' and achieve an efficient,
decentralized traffic light control. While the proposed self-control adapts
flexibly to local flow conditions and often leads to non-cyclical switching
patterns with changing service sequences of different traffic flows, an almost
periodic service may evolve under certain conditions and suggests the existence
of a spontaneous synchronization of traffic lights despite the varying delays
due to variable vehicle queues and travel times. The self-organized traffic
light control is based on an optimization and a stabilization rule, each of
which performs poorly at high utilizations of the road network, while their
proper combination reaches a superior performance. The result is a considerable
reduction not only in the average travel times, but also of their variation.
Similar control approaches could be applied to the coordination of logistic and
production processes
An Agent-Based Approach to Self-Organized Production
The chapter describes the modeling of a material handling system with the
production of individual units in a scheduled order. The units represent the
agents in the model and are transported in the system which is abstracted as a
directed graph. Since the hindrances of units on their path to the destination
can lead to inefficiencies in the production, the blockages of units are to be
reduced. Therefore, the units operate in the system by means of local
interactions in the conveying elements and indirect interactions based on a
measure of possible hindrances. If most of the units behave cooperatively
("socially"), the blockings in the system are reduced.
A simulation based on the model shows the collective behavior of the units in
the system. The transport processes in the simulation can be compared with the
processes in a real plant, which gives conclusions about the consequencies for
the production based on the superordinate planning.Comment: For related work see http://www.soms.ethz.c
Complex Dynamics of Bus, Tram and Elevator Delays in Transportation System
It is necessary and important to operate buses and trams on time. The bus
schedule is closely related to the dynamic motion of buses. In this part, we
introduce the nonlinear maps for describing the dynamics of shuttle buses in
the transportation system. The complex motion of the buses is explained by the
nonlinear-map models. The transportation system of shuttle buses without
passing is similar to that of the trams. The transport of elevators is also
similar to that of shuttle buses with freely passing. The complex dynamics of a
single bus is described in terms of the piecewise map, the delayed map, the
extended circle map and the combined map. The dynamics of a few buses is
described by the model of freely passing buses, the model of no passing buses,
and the model of increase or decrease of buses. The nonlinear-map models are
useful to make an accurate estimate of the arrival time in the bus
transportation
On stability analysis and parametric design of supply networks under the presence of transportation delays
International audienceManagement of interconnected manufacturing units, supply networks, constitutes a timely, but challenging problem in Physics, Operations Research and Mathematics, as it carries very rich dynamics. At the first stage, a very well understanding of the underlying mechanisms and interactions within the hierarchical construct of such networks is required. For this pursuit, a more realistic approach is proposed in this paper, which takes into account the presence of naturally existing transportation delays of supplies in between individual production units. In general, the presence of delays in the dynamics imports another source of instability, which needs to be addressed. However, it is well-known that a thorough stability analysis against delays carries complications, thus it is non-trivial. We present analytical techniques to tackle such difficulties, surfacing allowable transportation delays within the supply network that guarantees stable stock levels. This, in parallel, enables the selection of production rates assuring the supply network to operate in a stable regime. Moreover, we show that under certain parametric settings, the supply network dynamics may become highly sensitive against the presence of delays, which in turn, initiates an undesirable phenomenon called bullwhip effect. We present case studies demonstrating the bullwhip effect and suggesting parametric selections to avoid this undesired behavior within supply networks. Copyright © 2006 by ASME
Anticipative control of switched queueing systems
The relevant dynamics of a queueing process can be anticipated by taking future arrivals into account. If the transport from one queue to another is associated with transportation delays, as it is typical for traffic or productions networks, future arrivals to a queue are known over some time horizon and, thus, can be used for an anticipative control of the corresponding flows. A queue is controlled by switching its outflow between “on” and “off” similar to green and red traffic lights, where switching to “on” requires a non-zero setup time. Due to the presence of both continuous and discrete state variables, the queueing process is described as a hybrid dynamical system. From this formulation, we derive one observable of fundamental importance: the green time required to clear the queue. This quantity allows to detect switching time points for serving platoons without delay, i.e., in a “green wave” manner. Moreover, we quantify the cost of delaying the start of a service period or its termination in terms of additional waiting time. Our findings may serve as a basis for strategic control decisions. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200802.30.Yy Control theory, 02.30.Ks Delay and functional equations, 89.75.-k Complex systems, 89.40.-a Transportation,