This article considers the performance and development of car ownership forecasts, used by the department of transport in its evaluation of trunk road schemes, and it discusses their future development. The mathematical basis of the models is described in three appendices. All forecasts for the period 1962-1972 were based on an algebraic model known as the logistic function. This model which made no allowance for deviations in income and prices, constantly overpredicted car ownership after 1969. This simple model was revised in 1975 to incorporate specific income and price elasticities, and further revision took place in 1977 to incorporate a power growth function to describe the degree of non-linearity in the relationship between the absolute level of car ownership and its rate of change. Recent analysis of the family expenditure survey (fes), suggests that a stable relationship can be established between income, a car price index, and car ownership. The current national traffic forecasts are based on a combination of the aggregate and disaggregate approaches. A range of price estimates and rates of income growth were chosen to reflect the uncertainty of the future. The latest forecasts produce a band of curves predicting a saturation level of 0.5 or 0.4 cars per person. Because the evaluation of road schemes depends on uncertainties other than traffic forecasts, the size and effect of these other uncertainties is being investigated so that they can be incorporated into the model and so that the level where further refinement of the model ceases to be cost effective can be determined. (TRRL)

  • Availability:
  • Supplemental Notes:
    • The article is based on work carried out by the Transport and Road Research Laboratory, Crowthorne, Berks.
  • Corporate Authors:

    Her Majesty's Stationery Office

    Atlantic House, Holborn Viaduct
    London,   England 
  • Authors:
    • Giles, G E
    • WORSLEY, T E
  • Publication Date: 1979-8

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 99-108
  • Serial:
    • Economic Trends
    • Issue Number: 310
    • Publisher: Her Majesty's Stationery Office
    • ISSN: 0013-0400

Subject/Index Terms

Filing Info

  • Accession Number: 00322425
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • ISBN: 011 725577 7
  • Files: ITRD, TRIS
  • Created Date: May 21 1981 12:00AM