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Μόνιμο URI για αυτήν τη συλλογήhttps://dspace.library.tuc.gr/handle/123456789/125

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Global exponential stability for discrete-time networks with applications to traffic networks
(Institute of Electrical and Electronics Engineers, 2015) Karafyllis Iason; Καραφυλλης Ιασων; Papageorgiou Markos; Παπαγεωργιου Μαρκος
This paper provides sufficient conditions for global asymptotic stability and global exponential stability, which can be applied to nonlinear, large-scale, uncertain discrete-time networks. The conditions are derived by means of vector Lyapunov functions. The obtained results are applied to traffic networks for the derivation of sufficient conditions of global exponential stability of the uncongested equilibrium point of the network. Specific results and algorithms are provided for freeway traffic models. Various examples illustrate the applicability of the obtained results.
High-resolution relaxation approximations to second-order macroscopic traffic flow models
(Elsevier, 2014) Delis Anargyros; Δελης Αναργυρος; Nikolos Ioannis; Νικολος Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος
A novel numerical approach for the approximation of several, widely applied, macroscopic traffic flow models is presented. A relaxation-type approximation of second-order nonequilibrium models, written in conservation or balance law form, is considered. Using the relaxation approximation, the nonlinear equations are transformed to a semi-linear diagonilizable problem with linear characteristic variables and stiff source terms. To discretize the resulting relaxation system, low- and high-resolution reconstructions in space and implicit–explicit Runge–Kutta time integration schemes are considered. The family of spatial discretizations includes a second-order MUSCL scheme and a fifth-order WENO scheme, and a detailed formulation of the scheme is presented. Emphasis is given on the WENO scheme and its performance for solving the different traffic models. To demonstrate the effectiveness of the proposed approach, extensive numerical tests are performed for the different models. The computations reported here demonstrate the simplicity and versatility of relaxation schemes as solvers for macroscopic traffic flow models.
Integrated feedback ramp metering and mainstream traffic flow control on motorways using variable speed limits
(Elsevier, 2014) Carlson Rodrigo Castelan; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος
Ramp metering (RM) is the most direct and efficient tool for the motorway traffic flow management. However, because of the usually short length of the on-ramps, RM is typically deactivated to avoid interference of the created ramp queue with adjacent street traffic. By the integration of local RM with mainstream traffic flow control (MTFC) enabled via variable speed limits (VSL), control operation upstream of active bottlenecks could be continued even if the on-ramp is full or if the RM lower bound has been reached. Such integration is proposed via the extension of an existing local cascade feedback controller for MTFC-VSL by use of a split-range-like scheme that allows different control periods for RM and MTFC-VSL. The new integrated controller remains simple yet efficient and suitable for field implementation. The controller is evaluated in simulation for a real motorway infrastructure (a ring-road) fed with real (measured) demands and compared to stand-alone RM or MTFC-VSL, both with feedback and optimal control results. The controller’s performance is shown to meet the specifications and to approach the optimal control results for the investigated scenario.
Mainstream traffic flow control on freeways using variable speed limits
(ANPET - Associação Nacional de Pesquisa e Ensino em Transportes, 2013) Carlson Rodrigo Castelan; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος
Mainstream Traffic Flow Control (MTFC), enabled via variable speed limits, is a control concept for real-time freeway traffic management. The benefits of MTFC for efficient freeway traffic flow have been demonstrated recently using an optimal control approach and a feedback control approach. In this paper, both control approaches are reviewed and applied to a freeway network in a simulation environment. The validated network model used reflects an actual freeway (a ring-road), fed with actual (measured) demands. The optimal and feedback control results are discussed, compared and demonstrated to improve significantly the system performance. In particular, the feedback control scheme is deemed suitable for immediate practical application as it takes into account operational requirements and constraints, while its results are shown to be satisfactory. In addition, the control system performance was not very sensitive to variations of the parameters of the feedback controller. This result indicates that the burden associated with fine tuning of the controller may be reduced in the field.
Microsimulation analysis of practical aspects of traffic control with variable speed limits
(Institute of Electrical and Electronics Engineers, 2015) Papageorgiou Markos; Παπαγεωργιου Μαρκος; Muller Eduardo Rauh; Carlson Rodrigo Castelan; Kraus Werner
Mainstream traffic flow control (MTFC) with variable speed limits (VSLs) is a freeway traffic control method that aims to maximize throughput by regulating the mainstream flow upstream from a bottleneck. Previous studies in a macroscopic simulator have shown optimal and feedback MTFC potential to improve traffic conditions. In this paper, local feedback MTFC is applied in microscopic simulation for an on-ramp merge bottleneck. Traffic behavior reveals important aspects that had not been previously captured in macroscopic simulation. Mainly, the more realistic VSL application at specific points instead of along an entire freeway section produces a slower traffic response to speed limit changes. In addition, the nonlinear capacity flow/speed limit relation observed in the microscopic model is more pronounced than what was observed at the macroscopic level. After appropriate modifications in the control law, significant improvements in traffic conditions are obtained.

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