The reliability of using the gravity model for forecasting trip distribution: Introduction Approaches to gravity model calibration Bureau of public roads method of calibration Cell-by-cell regression method of calibration Accuracy measure Case study: City of Winnipeg Data acquisition Analysis of results Calibration results Forecasting with the calibrated model Conclusion and recommendations Acknowledgements References

Abstract

Abstract. The main purpose of this study is to assess the forecasting capability of the gravity model and to investigate the merit of including K-factors when using the model. Peak hour top data was obtained for four study year periods 1962, 1971, 1976 and 1981 for the City of Winnipeg. Analysis of the calibration results indicated that the Ffactors for the twenty year period were stable within a range of values. In general, however, the K-factors were found to be inconsistent from one prediction period to the next, and when used in forecasting tops they resulted in larger errors than without their use. The validity of using K-factors or the method which has been used to determine them is questionable. It was concluded that while K-factors are very meaningful in theory (as defined), they are not appropriate for use in predicting O-D matrices based on the method by which they are currently estimated (i.e. as a simple ratio). Further study is needed to investigate an alternative method of calibrating the gravity model such as the cell-by-cell regression method.