Road assignment—I: Principles and parameters of model formulation

Abstract

The factors which influence the formulation of road assignment models and the criteria by which different techniques may be compared and evaluated are discussed. In order to give the discussion a quantitative basis three basic parameters of network and model characteristics are defined: the degree of mathematical convergence achieved by the model (δ), the degree of individual variations in the perception of travel costs (ϵ 1), and the relative change in average travel costs due to congestion (ϵ 2). A number of general principles involving these parameters are proposed. The importance of intrinsic errors and of overall objectives in formulating an assignment model are also strongly stressed. Parts II and III of this paper (the following two articles) illustrate the application of these principles in more specific situations: the GLTS model where capacity restraint is a dominant factor, and the development of stochastic methods for situations where capacity effects are generally excluded.