Dynamic traffic control: Decentralized and coordinated methods.

An overall dynamic traffic management system that seeks to maximize network-wide performance is the primary focus of this research. Specifically, this dissertation deals with the development of efficient techniques for the dynamic control of signalization in traffic networks in the context of Intelligent Transportation Systems. It comprises three complementary components: decentralized control, coordinated control, and coordinated control in an Advanced Traveler Information System (ATIS) environment. For the first component, an algorithm to optimize, in real-time, traffic signals for individual intersections in traffic networks is presented; it uses an efficient decision-tree searching technique to minimize delay. This decentralized algorithm for traffic controllers is called Adaptive Limited Lookahead Optimization of Network Signals (ALLONS-D). Two perspectives are addressed as part of the second component: (i) a hierarchical control architecture for enabling local controllers to maximize system performance and (ii) an iterative process (ALLONS-I) to determine an equilibrium set of control policies for traffic-responsive signal controllers like ALLONS-D. The first perspective divides local signal choice and coordination of these local controllers into two layers of control. An optimization problem is formulated to determine the coordination requirements that are imparted to the local controllers from the higher layer. The ability of this scheme to improve performance on arterial and grid networks is tested via software simulation. In the same manner, this hierarchical scheme is shown to be useful in improving the flow of transit vehicles in a traffic signal network relying on ALLONS-D controllers. The second perspective for the second component of this dissertation deals with a form of coordination achieved by iteratively recalculating the signal control policies at the intersections; this iterative method is a dynamic adjustment process. This process is successful in converging to a set of coordinated traffic signals in some cases; its convergence properties are analyzed using a game-theoretic model. The result of this analysis is a proof of convergence for a specific class of traffic networks and traffic demand. Finally, the third component of this dissertation develops a traffic optimization process that incorporates drivers' route selections as well as the resulting adaptive traffic signal control policies. This iterative signal optimization - traffic assignment technique is developed and shown to converge to a dynamic user-equilibrium solution through simulation experiments and formal analysis. This iterative method allows an examination of the long term effect of the adaptive signal control scheme on drivers' route choices.Ph.D.Applied SciencesArtificial intelligenceElectrical engineeringOperations researchSocial SciencesSystems scienceTransportationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131305/2/9840627.pd

A Game-theoretic Approach to Signal Coordination

This paper addresses the coordination of traffic-responsive traffic signal controllers using an iterative process called ALLONS-I. It determines an equilibrium set of control policies for traffic-responsive signal controllers on a traffic network. This iterative method is a dynamic adjustment process that is successful in converging to a set of coordinated traffic signals in some cases; its convergence properties are analyzed using a game-theoretic model. The result of this analysis is a proof of convergence for a specific class of traffic networks and traffic demand using a traffic-responsive signal control scheme like ALLONS-D

Adaptive Look-ahead Optimization of Traffic Signals

ALLONS-D is a decentralized real-time traffic control scheme. A description of its basic architecture, system model, and optimization algorithm is given. Through simulations, the scheme is shown to be suitable for adaptive control of an isolated intersection. An efficient tree searching algorithm is used to find a traffic signal plan that minimizes delay. The search is constrained only by maximum and minimum green times per phase. This algorithm is free to consider cyclic and non-cyclic signal plans alike. The rolling horizon concept is used for the calculation and implementation of optimal signal plans. The ALLONS-D scheme has several key differences with other real-time traffic control schemes, such as OPAC. Extensive simulation experiments on a single intersection indicate the success of the ALLONS-D scheme versus any fixed-cycle plan. The tests included a full range of uniform and non-uniform demands from low levels of saturation to the over-saturated case. For arterial networks of..

On Combined Dynamic Traffic Assignment and Traffic-Responsive Signal Control

This paper is concerned with the analysis of the re-routing effects of traffic flow that are induced by traffic signals. This is done by the calculation of a dynamic userequilibrium traffic flow assignment using an iterative process. This iterative process is shown to be convergent through formal analysis and is studied by simulation experiments. Results from these simulation tests suggest that the type of traffic signal control and the exact signal plans used are key factors in accounting for shifts in traffic flows from drivers selecting different routes. Such re-routing is expected to be prevalent in an environment in which drivers are highly informed and can react to travel conditions throughout the day as is the case with the deployment of Advanced Traveler Information Systems (ATIS). In such an environment, fixed-signal plans (generated by non-adaptive signal controllers) may result in widely-varying traffic flows on links, degrading the ability of traffic engineers, and the driv..

Dynamic Traffic Control: Decentralized And Coordinated Methods

ALLONS-D is a decentralized real-time traffic control scheme. Through simulations, the scheme is shown to be suitable for adaptive control of an isolated intersection. An efficient tree searching algorithm, constrained only by a maximum and minimum green time per phase is used to find a traffic signal plan that minimizes delay. Differences between ALLONS-D & other real-time traffic control schemes, such as OPAC, are described. The scheme can also be used to reduce travel times on transit routes. For arterial networks of intersections, ALLONS-D is capable of inducing a level of coordination that results in progressive signal plans. An extension of the scheme to provide network-wide optimization of traffic signals is explained in the form of a two-layer scheme. Simulation experiments are performed with a newly developed simulator called STNS. INTRODUCTION In this paper, we provide a further description of ALLONS-D [1], a real-time traffic responsive strategy. ALLONS-D (Adaptive Limit..