Transportation models and their applications
Gonçalo Correia (TU Delft - Transport, Mobility and Logistics)
G.P. van Wee (TU Delft - Transport and Logistics)
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Abstract
Transport models have been defined in many ways and there are various kinds of models. In this chapter, a model is defined as a simplified representation of part of reality. The main goal of models is to estimate the behaviour of the real system in different scenarios (see Chapter 14) in a specific forecasting year. Possible outputs of these models may be, for example, the number of passenger kilometres in a country, region or city in a certain year or, often combining transport models and impact models, societally relevant outcomes in the area of accessibility, safety or the environment, and increasingly health. Models are often used to get an insight into the behaviour of the system in a do-nothing scenario and/or to gain an insight into the effects of proposed measures/policies on transport and other system-related components such as land use. Usually, not one but several futures are predicted whereby the effects of transport are computed for several scenarios concerning the socioeconomic development and policy variants (see Chapters 14 and 15).
This chapter provides readers with an introduction to how models work and shows what they can be used for. This knowledge should enable the reader to form an opinion as to whether a specific model can be used to answer certain questions. This chapter is focused on what are often called ‘strategic models’. These are models that aggregate volumes of travellers for a faster representation of mobility patterns in a city, region or country. In contrast, models for reproducing traffic flows on highways intended for real-time traffic management require modelling each vehicle. They are presented in Chapter 7 and are not dealt with in this chapter. At specific places in the text, we may refer to other modelling levels for the sake of distinction and clarification. For further insights into transport modelling, the authors recommend the book by Ortúzar and Willumsen (2011).
Section 16.2 provides an overview of strategic models. Section 16.3 introduces the concept of elasticity which is used in many strategic models. Section 16.4 discusses the traditional strategic aggregated models, while disaggregated models are discussed in section 16.5. Section 16.6 deals with model validation. Section 16.7 presents some examples of models currently used in the Netherlands. Section 16.8 addresses the question of what can and cannot be done using models. The main conclusions of the chapter are presented in section 16.9.