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A Model Based on Non-Homogeneity in Allocation Problems

Two basic types of activity allocation model, (1) behavioural or predictive models of the gravity type, and (2) planning or prescriptive models of the utility maximising type, are initially compared. Each has application to urban land use allocation, transport trip distribution and modal choice, but with different solution characteristics. A new type of model which may be either prescriptive or predictive is then developed in which non homogeneity or diversity of utility is introduced within each option. This model is utility maximising and is shown to be related to the gravity model and entropy maximising in which diversity is implied. Several features of the entropy approach may be explained in terms of diversity and utility maximisation with this model. The essential difference between the prescriptive and predictive versions then lies in the utility itself. In the prescriptive version, the utility of the community including externalities is appropriate. In the behavioural version, the utility of the decision maker which excludes these externalities is used. Thus the model presented may be used for each purpose, with appropriate utilities. These concepts are applicable to land use and travel modelling including modal choice. The integration of these new models in a strategic level model of the topaz type is considered. The resulting model might be used to (1) select optimal land use - transport plans, (2) predict the response of the community to them, and (3) determine policies to make the two compatible. The directions in which these studies may be extended are outlined (a).