Congestion in urban areas caused by incidents

Congestion is an everyday occurrence in most towns and cities during peak periods. Disruption caused by incidents is a major contributor, which, due to their unpredictability, can have a disproportionate impact leading occasionally to 'gridlock'. The report identifies the types and frequencies of incident and their impact in causing congestion, examines the interactions of the various factors which contribute to the formation of congestion, and outlines the steps needed for developing strategies to cope with incidents. It includes a theoretical investigation, and an examination of the practical aspects, identifying tools and a framework of techniques for coping with incidents and congestion generally. A variant of the CONTRAM time-dependent traffic assignment model, called CONTRAM-I, has been developed to model drivers' response to incidents, together with a congestion index for quantifying congestion. Desk studies using networks based on two towns are described, and some conclusions reached about the potential benefits of remedial actions. Further theoretical and modelling work would be needed to turn the framework into effective strategies, and to explore the interaction of these strategies with traffic control measures and driver information systems. (A)