Transport modelling provides the tools to describe and predict the movement of persons, goods and information in a given or possible future environment. It establishes relationships 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, often, specific aggregates of these flows) (Ortuzar and Willumsen, 1994; Schnabel and Lohse, 1997). The data needs vary considerably by the specific forms that those relationships take. It is not possible to discuss data needs without reference to the modelling framework to be supplied, although the orthodoxies for modelling and for data collection established by professional practice or government intervention or regulation seem to suggest otherwise. This chapter has therefore to select one of these pairings of data collection standard and modelling approach as the background of its discussion. The discrete choice-equilibrium framework and the personal survey approach, as the current state-of-the-art modelling and data collection approach coupling is a natural choice. The following discussion of the definition of movement and activity will first clarify the object of the modelling task and then discuss the difficulties of translating these definitions into survey or observation approaches. In Section 2 a brief discussion is given of the types of data generally collected in transport modelling to place the movement or activity data in context. Section 3 offers a consistent definition of movement and activity, while Section 4 discusses some of the specific issues arising in asking about movement and activities. Sections 5 and 6 address a number of the difficulties inherent in translating these definitions into survey approaches, by raising the issue of how to define the survey object and by describing the various survey approaches currently used.
Samenvatting