Chapter 16: Definition Of Movement and Activity For Transport Modelling

Transport modelling provides the tools to describe and predict the movements of persons, goods and information in a given or possible future environment. It establishes relations between the amounts, locations, characteristics and behaviours of persons, firms, infrastructures, services and environments to calculate flows by time, route, location, mode and service, or specific aggregates of these flows (Ortuzar and Willumsen, 2001; Schnabel and Lohse, 1997). The data needs vary considerably by the specific forms that those relations take. There is no place here to discuss the various relations used (see the relevant chapters below), but they can vary from rough aggregate models of area-wide flows to detailed agent-based micro-simulations of individual decision makers. Data availability and modelling approaches constrain and condition each other. For example, the assumption that income is not particularly relevant, will suggest that it should not be asked in a survey, but the known difficulties of obtaining accurate income information will at the same time encourage modellers to search for relationships without income as a variable. In retrospect, it becomes difficult to decide what came first: the data difficulties or the modelling idea. Equally, new theoretical insights into the behaviour of the system elements can spur the search for new data collection techniques and items, while new data collection approaches or technologies can invite modellers to adapt and enrich their approaches (Richardson et al., 1995; Axhausen, 1995).