Hypercongestion

The standard economic model for analysing traffic congestion incorporates a relationship between speed and traffic flow. Empirical measurements indicate a region, known as hypercongestion, in which speed increases with flow. We argue that this relationship is unsuitable as a supply curve for equilibrium analysis because observed hypercongestion occurs as a response to transient demand fluctuations. We then present tractable models for handling such fluctuations, both for a straight uniform highway and for a dense street network such as in a central business district (CBD). For the CBD model, we consider both exogenous and endogenous time patterns for demand, and we make use of an empirical speed-density relationship for Dallas, Texas, to characterise hypercongested conditions. The CBD model is adaptable to any situation where accumulation of work to be processed becomes such a hindrance as to reduce outflow. © The London School of Economics and the University of Bath 2003