Measuring Inaccuracy in Travel Demand Forecasting: Methodological Considerations Regarding Ramp Up and Sampling

Accuracy in travel demand forecasts is important for the effective allocation of scarce funds. This paper examines the methodological considerations involved in measuring accuracy of travel demand forecasts. 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 studies. The author 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. When interpreting the results from statistical analyses of inaccuracy in travel demand forecasting, this bias should be taken into account.

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  • English

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  • Accession Number: 01001223
  • Record Type: Publication
  • Files: TRIS, ATRI
  • Created Date: Jun 24 2005 1:04AM