SYSTEMATIC SENSITIVITY TESTING IN PROJECT APPRAISAL. A METHOD OF IDENTIFYING THE UNCERTAINTY OF TRANSPORTATION FORECASTS

Traditionally, the existence of an "end-state" which can be perfectly defined has been assumed in both land use and transportation planning. This is, however, a highly questionable assumption. In the case of transportation, predicting those quantities, such as population, employment, income and the like, which determine both the volume and characteristics of travel demand is very hazardous, particularly at the local level of detail required for any demand forecasting purposes; the longer the forecasting period, the greater is the likelihood of error and the likely size of that error. These errors are likely to be compounded by errors in the demand forecasting procedures themselves. Travel demand is a complex phenomenon and, even in the best of demand models, it is possible only to capture some of the factors and interactions which govern it. A further compounding factor is the likelihood of error in the data on which these models are based. Transportation planners need demand forecasts for the evaluation of plans and policies, and for a detailed design of projects. It is important that the errors and uncertainties intrinsic in the forecasting process be recognised and explicitly treated. In this paper, the authors first review some of the sources of error and uncertainty. The authors then look briefly at some of the ways in which uncertainty can be treated in decision-making. This is followed by a description of a technique developed in the specific context of the appraisal of inter-urban highway projects in the United Kingdom. Finally, the authors discuss how such an appraisal, based on systematic sensitivity testing, could be applied to a wider variety of plans and policies. (TRRL)

  • Supplemental Notes:
    • Transportation Planning Research Colloquium 1983 held in Zandvoort on December 14-16, 1983. Volume II.
  • Corporate Authors:

    Colloguium Vervoersplanologisch Speurwerk

    P.O. Box 45
    Delft,   Netherlands 
  • Authors:
    • Richards, M G
    • Bovy, P H L
  • Publication Date: 1984

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Filing Info

  • Accession Number: 00389272
  • Record Type: Publication
  • Source Agency: Institute for Road Safety Research, SWOV
  • Files: ITRD, TRIS
  • Created Date: Oct 30 1984 12:00AM