THE FOUR-STEP MODEL. IN: HANDBOOK OF TRANSPORT MODELLING

Abstract

The history of demand modeling for person travel has been dominated by the modeling approach, which has come to be referred as the four-step model (FSM). Travel, always viewed in theory as derived from demand for activity participation, in practice has been modeled with trip-based rather than activity-based methods. Trip origin-destination (O-D) rather than activity surveys from the principal database. The influence of activity characteristics decreases, and that of trip characteristics increases, as the conventional forecasting sequence proceeds. The application of this modeling approach is near universal, as in large measure are its measure are its criticisms. The current FSM might best be viewed in tow stages. In the first stage, various characteristics of the traveler and the land use - activity system (and, to a varying degree, the transportation system) are evaluated, calibrated, and validated to produce a non-equilibrated measure of travel demand (or trip tables). In the second stage, this demand is loaded onto the transportation network in a process that amounts to forma equilibration of route choice only, not of other choice dimensions, mode, time-of-day, or whether to travel at all (feedback to prior stages has often been introduced, but not in a consistent and convergent manner). Although this approach has been moderately successful in the aggregate, it has failed to perform in most relevant policy tests, whether on the demand or supply side.

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