Opening out and closing down: the treatment of uncertainty in transport planning’s forecasting paradigm

Abstract

Since the 1960s, development of the transport system has been framed by the notion of forecasting future demand. Yet the past decade or more appears to signal some significant changes to the role of travel in society which are having a material impact on how much people travel (and may travel in the future). Coupled with the potential for major technological changes and a range of climate adaptation scenarios, the future of mobility presents today's decision making on transport strategy and investment with a broader set of uncertainties than has previously been considered. This paper examines current mainstream practice for incorporating uncertainty into decision-making, through an illustrative case study of the highly codified approaches of the Department for Transport in England. It deconstructs the issue by first focussing on different ways in which there is an opening out or acceptance of new uncertainties and how this creates a (wider) set of potential futures. It then turns to consider how this set of futures is used, or not, in decision-making, i.e. the process of closing down uncertainty to arrive at or at least inform a decision. We demonstrate that, because the range of uncertainties has broadened in scope and scale, the traditional technocratic approach of closing down decisions through sensitivity testing is at odds with the greater breadth now being called for at the opening out stage. We conclude that transport decision-making would benefit from a rebalancing of technical depth with analytical breadth. The paper outlines a plausible new approach to opening out and closing down that is starting to be applied in practice. This approach must be accompanied by an opening up of the processes by which technical advice for decisions are reached and how uncertainties are understood and negotiated.

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