The first part of this paper argues that the variable "cars per household', as well as the proportion of households owning more than a given number of cars, should be modelled by sigmoid functions with finite saturation levels. Next, a summary and critique of the work of the RHTM group is presented. Problems relating to choice of functional form, interaction of effects, and the usefulness of the explanatory variable "car purchasing income" are discussed. This leads to an analysis of the concept of a saturation level, with a caution against using external data to determine it when the true functional form of the car ownership growth path is unknown. Following this, TRRL work is discussed and its limitations highlighted. Data for the period 1953-1974 is reworked yielding the conclusion that there is no evidence that growth in this period has been non-logistic. This implies that previous overpredictions by TRRL were due to incorrect parameter estimates, rather than the choice of the wrong model form. (a) (TRRL)

  • Corporate Authors:

    University of Leeds

    School of Geography, Woodhouse Lane
    Leeds, West Yorkshire  England  LS2 9JT
  • Authors:
    • FOWKES, A S
    • PEARMAN, A D
    • BUTTON, K J
  • Publication Date: 1979-4

Media Info

  • Features: Figures; References; Tables;
  • Pagination: n.p.

Subject/Index Terms

Filing Info

  • Accession Number: 00324584
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Report/Paper Numbers: Working Paper 110
  • Files: ITRD, TRIS
  • Created Date: May 21 1981 12:00AM