ON THE CALIBRATION OF THE GRAVITY MODEL

Knowledge of Origin-Destination (OD) trip matrices is needed in many stages of transport planning. As direct observations of OD-flows are usually not available, a commonly used approach is to estimate them from traffic counts and other aggregated flow constraints. The under-specification that characterises this estimation process can be resolved by requiring that OD-values conform to a model of travel demand. In this paper a class of methods based on the gravity model, with either an exponential or a piecewise constant deterrence function, is considered. Numerical methods to calibrate these models from traffic counts and establish a unifying analysis of them are focused on. The paper starts with a description of the gravity model, and a summary of the assumed modelling and observation error structures. Subsequently a likelihood expression is established which we seek to maximise. The paper then concentrates on methods that can be used for this purpose. Existing methods are discussed, and it is shown that some of the difficulties that occur when applying them can be resolved by a change of variables to logarithms of the model parameters. A key result concerns the matrix of second derivatives of the likelihood function. This result is then applied and leads to a new optimisation method. In a series of experiments this method is shown to be robust and computationally efficient. For the covering abstract, see IRRD 889300.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/0860502945
• Corporate Authors:

  PTRC Education and Research Services Limited

  Glenthorne House, Hammersmith Grove
  London W6OL9,   England 
• Authors:
  • Van der Zijpp, N J
  • Heydecker, B G
• Conference:
  • TRANSPORTATION PLANNING METHODS. PROCEEDINGS OF SEMINAR D HELD AT THE PTRC EUROPEAN TRANSPORT FORUM, BRUNEL UNIVERSITY, ENGLAND, 2-6 SEPTEMBER 1996. VOLUME P404-1
• Publication Date: 1996

Language

• English

Media Info

• Features: References;
• Pagination: 15 p.

Subject/Index Terms

• TRT Terms: Calibration; Conferences; Errors; Forecasting; Gravity models; Mathematical models; Matrices (Mathematics); Methodology; Optimization; Origin and destination; Probability; Traffic counts; Travel
• Uncontrolled Terms: Optimum
• ITRD Terms: 6171: Calibration; 8525: Conference; 6440: Error; 132: Forecast; 690: Gravity model; 698: Journey; 6473: Mathematical model; 6494: Matrix; 9102: Method; 687: Origin destination traffic; 6534: Probability; 689: Traffic count
• Subject Areas: Data and Information Technology; Operations and Traffic Management;

Filing Info

• Accession Number: 00737497
• Record Type: Publication
• Source Agency: Transport Research Laboratory
• ISBN: 0-86050-294-5
• Files: ITRD, ATRI
• Created Date: Jun 27 1997 12:00AM