This paper presents a review of traffic control as applied to congested or over-saturated conditions. The paper begins with an introduction to traffic control in general, it then goes on to describe types of congestion, objectives for congestion control and some approaches to congestion control. Although the paper is mainly concerned with traffic signal control, other measures such as road pricing are described briefly. More and more, traffic engineers have realized that existing traffic signals fail to perform satisfactory under prolonged congestion or over-saturated conditions. The paper identifies a number of theoretical studies which attempt to deal with such problems. It then describes the following traffic control systems, OPAC, PRODYN, SAGE, SCATS, SCOOT, STAUKO and UTOPIA, some more developed than others, and discusses their ability to deal with congestion. The paper presents the author's conclusions and recommendations for future research in the development of over-saturation strategies. (A)
Abstract