The traditional urban transportation planning process has mobility at its centre: either as something to be facilitated (e.g. because it is assumed it would fuel economic growth, or support social emancipation, as in the ‘predict and provide’ paradigm) or as something to be constrained (e.g. because of negative environmental and social impacts, as in the ‘predict and prevent’ paradigm) (Owens, 1995). The process is epitomized by the so-called urban transportation modelling system (UTMS), also popularly known as the ‘four-step model’ because of the four analytical steps it entails: estimation of trip generation (how many trips?), trip distribution (from where to where?), modal choice (by which transport mode?), and trip assignment (on which routes?) (Meyer and Miller, n.d.). The UTMS has long been criticized – most notably for the lack of a sound behavioural base – but it still permeates transport demand analysis, among more complex alternative models with a more sound behavioural basis (e.g. random utility models, activity-based models). In the context of the view of urban mobility issues embraced in this book the problem with the UTMS is, however, more fundamental. Central to the approach is the notion that at the start of the urban transportation planning process should be the prediction of future mobility demand, whether it is to facilitate it (as in ‘predict and provide’) or constrain it (as in ‘predict and prevent’).
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