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Understanding the role of the forecast-maker in overestimation forecasts of policy impacts: The case of Travel Demand Management policies

  • Tal, Gil
  • Cohen-Blankshtain, Galit
Registered author(s):

    Forecasting the impacts of a proposed policy is an important component of the transportation planning and decision making process. Although scientific tools are often used in transportation forecasts, biases and, more specifically, overestimations of the expected impact are often observed. This study explores the correlations between forecast-maker's characteristics and forecast bias creation and reduction. The study examines two transport-related policies aiming at the reduction of car use: telecommuting and carsharing. Both are Travel Demand Management (TDM) policies, which attract much attention from transport experts. We tested the extent to which the forecast-maker's beliefs about the policy at stake affected the forecast bias. We found that attitudes and beliefs associates not only with overestimation bias but also with its reduction over time. We also tested the extent to which the forecast-maker's affiliation, the performing institute and the publication type were correlated with the biases of the forecast and with the forecaster attitudes and beliefs. These characteristics are intuitively used by the forecast user as tools to assess the 'objectivity' of the forecast, but our analysis found no association between these characteristics and the forecast bias.

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    Article provided by Elsevier in its journal Transportation Research Part A: Policy and Practice.

    Volume (Year): 45 (2011)
    Issue (Month): 5 (June)
    Pages: 389-400

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    Handle: RePEc:eee:transa:v:45:y:2011:i:5:p:389-400
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    1. Sangho Choo & Patricia L. Mokhtarian & Ilan Salomon, 2005. "Does Telecommuting Reduce Vehicle-miles Traveled? An Aggregate Time Series Analysis for the U. S," Econometrics 0505001, EconWPA.
    2. Martin, Elliot & Shaheen, Susan Alison & Lidicker, Jeffrey, 2010. "Carsharing’S Impact On Household Vehicle Holdings: Results From A North American Shared-Use Vehicle Survey," Institute of Transportation Studies, Working Paper Series qt0850h6r5, Institute of Transportation Studies, UC Davis.
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    9. David Laster & Paul Bennett & In Sun Geoum, 1999. "Rational Bias In Macroeconomic Forecasts," The Quarterly Journal of Economics, MIT Press, vol. 114(1), pages 293-318, February.
    10. Shaheen, Susan & Sperling, Daniel & Wagner, Conrad, 1998. "Carsharing in Europe and North American: Past, Present, and Future," University of California Transportation Center, Working Papers qt4gx4m05b, University of California Transportation Center.
    11. Kahneman, Daniel & Tversky, Amos, 1979. "Prospect Theory: An Analysis of Decision under Risk," Econometrica, Econometric Society, vol. 47(2), pages 263-91, March.
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    14. Marshall, Stephen & Banister, David, 2000. "Travel reduction strategies: intentions and outcomes," Transportation Research Part A: Policy and Practice, Elsevier, vol. 34(5), pages 321-338, June.
    15. Tal, Gil, 2008. "Overestimation Reduction in Forecasting Telecommuting as a TDM Policy," Institute of Transportation Studies, Working Paper Series qt1qk959v1, Institute of Transportation Studies, UC Davis.
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