Task 6.1 Development of Car Ownership Model Specification

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As a matter of principle, before starting any aspect of the calibration of the Wellington Transport Strategy Model, we sought to specify much of the transport model form in advance so as to maximise the efficiency of the calibration process and avoid wasting time pursuing unfruitful analyses. The material included here was all developed as part of the preparation of the Technical Specification at the outset of the project, well before the calibration of this transport model.

The broad specification of the car ownership model was decided:
* a model of household car ownership: whether households owned 0, 1 or 2 or more cars
* the model would be segmented by household type: by the number of adults (1, 2 or 3+) and whether or not the household could be classified as retired.

A number of design issues needed to be considered and resolved regarding this specification:
  1. whether to combine this cross-sectional car ownership model with the forecasts of a time series car ownership model;
  2. whether to distinguish households owning 3 or more cars;
  3. the role of accessibility terms in the car ownership model;
  4. the role of census data in fitting the base year car ownership model;
  5. how best to implement the car ownership model and the role of sample enumeration.
  6. This culiminated in a final technical specification of the car ownership model.