Apostolos Kotsialos

Review of road traffic control strategies

Traffic congestion in urban road and freeway networks leads to a strong degradation of the network infrastructure and accordingly reduced throughput, which can be countered via suitable control measures and strategies. After illustrating the main reasons for infrastructure deterioration due to traffic congestion, a comprehensive overview of proposed and implemented control strategies is provided for three areas: urban road networks, freeway networks, and route guidance. Selected application results, obtained from either simulation studies or field implementations, are briefly outlined to illustrate the impact of various control actions and strategies. The paper concludes with a brief discussion of future needs in this important technical area.

Freeway ramp metering: an overview

Recurrent and nonrecurrent congestion on freeways may be alleviated if todays spontaneous infrastructure utilization is replaced by an orderly, controllable operation via comprehensive application of ramp metering and freeway-to-freeway control, combined with powerful optimal control techniques. This paper first explains why ramp metering can lead to a dramatic amelioration of traffic conditions on freeways. An overview of ramp metering algorithms is provided next, ranging from early fixed-time approaches to traffic-responsive regulators and to modern sophisticated nonlinear optimal control schemes. Finally, a large-scale example demonstrates the high potential of advanced ramp metering approaches.

Coordinated and integrated control of motorway networks via non-linear optimal control

The problem of designing integrated traffic control strategies for motorway networks with the use of ramp metering, route guidance, and motorway-to-motorway control measures is considered in this paper. A generic problem formulation is presented in the format of a discrete-time optimal control problem whose numerical solution is achieved by use of a feasible-direction algorithm. As an illustrative example, a relatively simple motorway network is considered under different control scenarios. In each case the optimal control strategy is discussed along with its effect on the traffic flow process. The results demonstrate the efficiency of the proposed approach as well as the genuinely intelligent behaviour of the designed control strategy.

Traffic flow modeling of large-scale motorway networks using the macroscopic modeling tool METANET

This paper employs previously developed modeling, validation, and stimulation tools to address, for the first time, the realistic macroscopic simulation of a real large-scale motorway network. More specifically, the macroscopic simulator METANET, involving a second-order traffic flow model as well as network-relevant extensions, is utilized. A rigorous quantitative validation procedure is applied to individual network links, and subsequently a heuristic qualitative validation procedure is employed at a network level. The large-scale motorway network around Amsterdam, The Netherlands, is considered in this investigation. The main goal of the paper is to describe the application approach and procedures and to demonstrate the accuracy and usefulness of macroscopic modeling tools for large-scale motorway networks.

Nonlinear optimal control applied to coordinated ramp metering

The goal of this paper is to describe a generic approach to the problem of optimal coordinated ramp metering control in large-scale motorway networks. In this approach, the traffic flow process is macroscopically modeled by use of a second-order macroscopic traffic flow model. The overall problem of coordinated ramp metering is formulated as a constrained discrete-time nonlinear optimal control problem, and a feasible-direction nonlinear optimization algorithm is employed for its numerical solution. The control strategys efficiency is demonstrated through its application to the 32-km Amsterdam ring road. A number of adequately chosen scenarios along with a thorough analysis, interpretation, and suitable visualization of the obtained results provides a basis for the better understanding of some complex interrelationships of partially conflicting performance criteria. More precisely, the strategys efficiency and equity properties as well as their tradeoff are studied and their partially competitive behavior is discussed. The results of the presented approach are very promising and demonstrate the efficiency of the optimal control methodology for motorway traffic control problems.

Optimal Coordinated Ramp Metering with Advanced Motorway Optimal Control

A generic approach to the problem of optimal coordinated ramp metering control in large-scale motorway networks is described that is implemented in the software tool Advanced Motorway Optimal Control. In this approach, the traffic flow process is modeled by use of a secondorder macroscopic traffic flow model. The overall problem of coordinated ramp metering is formulated as a constrained discrete-time nonlinear optimal control problem, and a feasible-direction nonlinear optimization algorithm is employed for its numerical solution. The control strategy’s efficiency is demonstrated through its application to the 32-km long Amsterdam ring road. A number of different scenarios with regard to the number of controlled ramps and the available storage space are discussed in some detail. The results of the presented approach are very promising and demonstrate the high efficiency and general applicability of the optimal control methodology for motorway traffic control problems.

Motorway network traffic control systems

Abstract This paper reviews the methods used for the design of motorway network traffic control strategies. Various control strategies for the available control measures are discussed in terms of their design and their operating features, including ramp metering, route guidance, and link control. An example of an advanced coordinated ramp metering control strategy which is based on large-scale optimisation and is applied to the Amsterdam ring-road is presented.

Efficiency versus fairness in network-wide ramp metering

The advanced motorway optimal control (AMOC) strategy for optimal network-wide ramp metering is applied to the ring-road of Amsterdam, the Netherlands, with the aim of investigating some important and interesting problems arising in ubiquitous ramp metering. A number of adequately chosen scenarios along with a thorough analysis, interpretation, and suitable visualisation of the obtained results provides a basis for the better understanding of some complex interrelationships of partially conflicting performance criteria. More precisely, the strategys efficiency and fairness properties as well as their trade-off are studied and their partially competitive behaviour is discussed. This trade-off is implicitly addressed by the AMOC strategy through consideration of the available ramp storage space, something which may be used as a tool to establish a desired policy of the systems efficiency versus fairness.

Local and Optimal Coordinated Ramp Metering for Freeway Networks

In this article a nonlinear model predictive control approach to the problem of coordinated ramp metering is presented. The previously designed optimal control tool Advanced Motorway Optimal Control (AMOC) is used within the framework of a hierarchical control structure which consists of three basic layers: the estimation/prediction layer, the optimization layer, and the direct control layer. More emphasis is given to the last two layers where the control actions on a network-wide and on a local level, respectively, are decided. The hierarchical control strategy combines AMOCs coordinated ramp metering control with local feedback Asservissement LInéaire dEntré Autoroutière (ALINEA) control in an efficient way. Simulation investigations for the Amsterdam ring-road are reported whereby the results are compared with those obtained by applying ALINEA as a stand-alone strategy. It is shown that the proposed control scheme is efficient, fair, and real-time feasible.

Integrated optimal control of motorway traffic networks

The problem of designing integrated traffic control strategies for motorway networks with the use of ramp metering, motorway-to-motorway control, and route guidance is considered. A generic problem formulation is presented in the format of a discrete-time optimal control problem whose numerical solution is achieved by use of a nonlinear optimisation method. As an illustrative example, a relatively simple motorway network is considered under different control scenarios. The results demonstrate the efficiency of the proposed approach as well as the intelligent behaviour of the designed control strategy.