Following development within the Department of Transport of a new national model of long-distance road traffic, Howard Humphreys were commissioned by the Department to audit, assess and report on the quality of information provided by the model, with guidelines and advice for its use by local teams. The work of the consultants was to be primarily concerned with an 'external' validation of the output matrices, while an 'internal' validation of the model itself was to be undertaken by the Institute for Transport Studies of Leeds University. In the event, the extent to which new statistical techniques were developed and utilised meant that the work of the two teams was closely inter-related. The external validation was based upon the methodology and computer programs which had been developed by the consultants--Howard Humphreys and Transportation Planning Associates--in parallel with the evolution of the traffic appraisal manual (and as reported upon at the 1981 sam). The base data fell into two categories - that which had been collected during the RHTM project and input to the calibration, and independent but compatible survey data which could be processed within the resources available for the project. Analyses of the differences between observed and synthesised matrix cell values gave a measure of the errors associated with the fact that the model could not adequately represent the complexity of trip distribution. A parallel procedure enabled an approximation to be made of the matrix cell variability due to the inherent variability of the data input to the calibration, including the trip ends. Combining these analyses enabled estimates to be made of the total accuracy of the model matrices due to all the factors involved. The results of this work were then related to the way in which the matrices might be used by those involved in the appraisal of highway schemes. (Author/TRRL)

  • Availability:
  • Supplemental Notes:
    • This paper was presented during the proceedings of Seminar Q held at PTRC's 10th Annual Summer Meeting, Transportation Analysis and Models, Warwick University, England.
  • Corporate Authors:

    PTRC Education and Research Services Limited

    110 Strand
    London WC2,   England 
  • Authors:
    • Wyley, W J
  • Conference:
  • Publication Date: 1982

Media Info

  • Features: Figures; Tables;
  • Pagination: p. 245-257

Subject/Index Terms

Filing Info

  • Accession Number: 00381636
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • ISBN: 0-86050-113-2
  • Report/Paper Numbers: REPORT
  • Files: ITRD, TRIS
  • Created Date: Apr 30 1984 12:00AM