Network Topology and the Efficiency of Equilibrium

Different kinds of networks, such as transportation, communication, computer, and supply networks, are susceptible to similar kinds of inefficiencies. These arise when congestion externalities make each user's cost depend on the other users' choices of routes. If each user chooses the least expensive (e.g., fastest) route from the users' common point of origin to the common destination, the result may be inefficient in the sense that there is an alternative assignment of routes to users that reduces the costs of all users. However, this may happen only for certain kinds of network topologies. This paper gives several alternative characterizations of networks in which inefficiencies may occur. In particular, a necessary and sufficient condition for inefficiency is that one of several specific, simple networks is embedded in the network. Keywords: Congestion, network topology, Braess's paradox, transportation networks, Wardrop equilibrium. 2 1

Comparisons of Urban Travel Forecasts Prepared with the Sequential Procedure and a Combined Model

Detailed analyses and comparisons of urban travel forecasts prepared by applying the state-of-practice sequential procedure and the solution of a combined network equilibrium model are presented. The sequential procedure for solving the trip distribution, mode choice and assignment problems with feedback is the current practice in most transportation planning agencies, although its important limitations are well known. The solution of a combined model, in contrast, results from a single mathematical formulation, which ensures a well-converged and consistent result. Using a real network, several methods for solving the sequential procedure with feedback are compared to the solution of the combined model ESTRAUS. The results of these methods are shown to have various levels of instability. The paper concludes with a call for a new paradigm of travel forecasting practice based on an internally consistent model formulation that can be solved to a level of precision suitable for comparing alternative scenarios. Copyright Springer Science + Business Media, LLC 2006Combined network equilibrium models, Sequential procedure, Urban travel forecasting,

A retrospective on Beckmann, McGuire and Winsten's "Studies in the Economics of Transportation"

This article describes the impact and influence of the book, "Studies in the Economics of Transportation", by M. Beckmann, C.B. McGuire and C.B. Winsten, published in 1956 by Yale University Press. Our focus is on the book's impacts on innovations in modeling, methodological developments and applications in transportation, regional science and other disciplines, which continue to this day. Copyright RSAI 2005.