“Prediction is very difficult, especially if it’s about the future”

drgregmarsden

In this second post about the work of the Commission on Travel Demand I will explore the challenges posed by the quote from the scientist Nils Bohr that headlines this article.

Lets start by looking at the state of practice in the UK. All major infrastructure schemes are subject to an economic appraisal with an appraisal period of 60 years (which is 30 years longer than it used to be a decade ago). We produce long term estimates of demand using the National Trip End Model and a suite of other tools such as the National Transport Model and the Passenger Demand Forecasting Handbook. However, the demand futures upon which decisions are based are largely determined by what are deemed to be ‘reasonable assumptions’. The case for HS2 for example includes the following acknowledgment: “Despite the economic downturn there is little evidence to suggest the recent strong growth in long…

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