I was recently in Copenhagen, where I gave a keynote talk at the UNITE Conference (Uncertainty in Transport Evaluation) at DTU. My thanks to the organizers for inviting me. (I really liked Copenhagen, more on that in a later post).
My talk was titled: Evaluation in a Time of Uncertainty
Abstract: We live in a world where the future is increasingly unpredictable. How should we evaluate transportation investments? Should we even try to evaluate investments in advance? What do we know about what people value? This talk will consider directions in transportation evaluation, and suggestions for better decision-making given uncertainty.
The slide deck is here.
The essential tension in my presentation is the hypothesis that essentially “Long-term forecasting is impossible” vs. my argument that forecasting can only be improved if we “Make forecasters responsible for forecasts.”
David Levinson, Transportist 
Given the number of factors which are beyond the forecaster’s control (government policies among other things), this seems to be an irreconcilable problem. Forecasters may be willing to offer a wider range of outcome scenarios (with associated probabilities), but decision makers are generally not in a position to evaluate this type of input. In my recent experience as a consultant, it seems that trying to “make forecasters responsible for forecasts” is generally done by transferring the financial risk onto them. and this may actually have the unintended consequence of forcing them out of the forecasting business.
In my opinion, decision makers need to come to terms with the fact that forecasters cannot provide them with a crystal ball to predict the future. Decisions will always need to be made with much uncertainty. Forecasting is just one part of the process. Implementation is perhaps even more important. If we want something to happen in the way that it was forecast to happen (assuming that is what we want), then we also need to consider marketing, education, and various other incentives….
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