Measuring inaccuracy in travel demand forecasting: Methodological considerations regarding ramp up and sampling

Flyvbjerg, Bent (2005) Measuring inaccuracy in travel demand forecasting: Methodological considerations regarding ramp up and sampling. Transportation Research. Part A: Policy and Practice, 39 (6). pp. 522-530.

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Abstract

Project promoters, forecasters, and managers sometimes object to two things in measuring inaccuracy in travel demand forecasting: (1) using the forecast made at the time of making the decision to build as the basis for measuring inaccuracy and (2) using traffic during the first year of operations as the basis for measurement. This paper presents the case against both objections. First, if one is interested in learning whether decisions about building transport infrastructure are based on reliable information, then it is exactly the traffic forecasted at the time of making the decision to build that is of interest. Second, although ideally studies should take into account so-called demand “ramp up” over a period of years, the empirical evidence and practical considerations do not support this ideal requirement, at least not for large-N studies. Finally, the paper argues that large samples of inaccuracy in travel demand forecasts are likely to be conservatively biased, i.e., accuracy in travel demand forecasts estimated from such samples would likely be higher than accuracy in travel demand forecasts in the project population. This bias must be taken into account when interpreting the results from statistical analyses of inaccuracy in travel demand forecasting.

Item Type: Article
Keywords: Travel demand forecasting; inaccuracy of travel forecasts; demand ramp up; sampling for measuring inaccuracy; bias
Subject(s): Project management
Centre: BT Centre for Major Programme Management
Date Deposited: 25 Mar 2011 12:16
Last Modified: 23 Oct 2015 14:05
URI: http://eureka.sbs.ox.ac.uk/id/eprint/729

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