Markos Papageorgiou

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.

Modelling and real-time control of traffic flow on the southern part of Boulevard Peripherique in Paris: Part I: Modelling

Abstract A microscopic mathematical model of freeway traffic flow is applied to a 6 km stretch of the Boulevard Peripherique in Paris including several on-ramps and off-ramps. The model is validated on the basis of real traffic flow measurements selected under a broad spectrum of traffic conditions. The mathematical model is capable of describing complicated traffic phenomena with considerable accuracy. A simulation program which is developed on the basis of the modelling equations may be used as a tool for testing of control strategies. Development and testing of control strategies is the strategies is the subject of a subsequent paper.

DYNAMIC MODELING, ASSIGNMENT, AND ROUTE GUIDANCE IN TRAFFIC NETWORKS

A macroscopic modeling framework for dynamic traffic phenomena on multidestination freeway and/or road networks with time varying demands is developed. A key variable of the model at each network node are the splitting rates of each traffic subflow with a specific destination. Two approaches are investigated for resolving the dynamic assignment and the route guidance problem: first, an optimal control approach for achieving a dynamic system or user optimum; second, a feedback concept for establishing dynamic user optimal conditions. The overall approach allows for integrated design of individual and/or collective route guidance, ramp metering, and signal setting in freeway and/or road networks. Some examples are provided.

Overview of Road Traffic Control Strategies

Abstract 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 concise overview of proposed and implemented control strategies is provided for three areas: urban road networks, freeway networks and route guidance. The paper concludes with a brief discussion of future needs in this important technical area.

A MULTIVARIABLE REGULATOR APPROACH TO TRAFFIC-RESPONSIVE NETWORK-WIDE SIGNAL CONTROL

The paper presents the design approach, the objectives, the development, the advantages, and some application results of the traffic-responsive urban control (TUC) strategy. Based on a store-and-forward modelling of the urban network traffic and using the linear-quadratic regulator theory, the design of TUC leads to a multivariable regulator for traffic-responsive co-ordinated network-wide signal control that is particularly suitable also for saturated traffic conditions. Simulation investigations demonstrate the efficiency of the proposed approach. Results of TUCs first field implementation and evaluation are also presented. Finally, summarising conclusions are drawn and future work is outlined.

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.

Modelling and real-time control of traffic flow on the southern part of Boulevard Peripherique in Paris: Part II: Coordinated on-ramp metering

Abstract A coordinated, feedback ramp metering strategy is derived for the southern part of Boulevard Peripherique in Paris. The derivation is based on well-known methods of Automatic Control theory (Linear Quadratic Optimisation) using a linearized version of a nonlinear macroscopic traffic flow model presented in a preceding paper. Efficiency of the presented strategy is tested and compared to no control, fixed-time control, and local feedback control on the basis of simulation investigations.

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.

Effects of Variable Speed Limits on Motorway Traffic Flow

Variable speed limits (VSLs) displayed on roadside variable message signs (VMSs) have emerged as a widespread traffic control measure on motorways in many countries, leading to substantial traffic safety benefits; however, there is no clear evidence of improved traffic flow efficiency in operational VSL systems. The available information on VSL impact on aggregate traffic flow behavior is summarized, and the issue is investigated in more detail with real traffic data from a European motorway. It is found that VSLs decrease the slope of the flow–occupancy diagram at undercritical conditions, shift the critical occupancy to higher values, and enable higher flows at the same occupancy values in over-critical conditions. Implications of the derived findings for more efficient VSL control strategies are discussed.

Brief paper: Parameter identification for a traffic flow model

In this paper, a macroscopic model is presented which describes the traffic flow on a freeway by a set of nonlinear, deterministic difference equations. The model is deduced from simple physical and empirical considerations and contains a set of free parameters which have to be estimated using real traffic data. This identification procedure is formulated here as a parameter optimization problem which is solved by nonlinear programming. In addition, the sensitivity of the model with respect to parameter changes and structural changes is investigated. Although stochastic events play a role in traffic dynamics, the results demonstrate that the validated model copes surprisingly well with real traffic behaviour.