John Polak
Imperial College London
, London, United Kingdom, Jan-Dirk Schmoecker, Centre for Transport Studies
Imperial College London, London, United Kingdom, Fabian Bastin, Cerfacs, , France
Dynamic Discrete Choice with an Inter-temporal Resource Constraint - The Case of Door-to-Door Concessionary Travel in London (assigned to theme
Recent theoretical advances in the specification and estimation of discrete choice models have enabled such techniques to be applied to increasingly complex travel decision making processes characterised for example by complex patterns of substitution, heterogeneity in tastes and heteroskedascity in unobservables. However, one important class of travel choice problems that has to date received little attention in the literature are those that arise when repeated choices are made subject to an inter-temporal resource constraint. Such problems arise in a number of contexts such as with certain forms of pre-paid public transport ticket product and with certain concessionary travel arrangements. The salient characteristic of such problems is that, over some relevant time horizon, there exists a constraint (direct or indirect) on the frequency with which certain choices can be made. Such constraints induce complex inter-dependencies amongst decisions in different time periods. Related problems have received some attention in other areas (e.g., environmental economics) and such constraints are potentially of considerable relevance to problems of environmental management in transport. The objective of this paper is to examine a particular example of such a travel choice process which arises in the provision of concessionary door-to-door travel for the elderly and disabled in London. These concessionary arrangements are provided by a combination of dial-a-ride bus and taxi and eligible individuals receive separate monthly trip budgets for each mode. We use data collected as part of a study undertaken to evaluate the effectiveness of alternative budget regimes. These data describe the concessionary trips made by a sample of several hundred eligible individuals over a period of approximately two years, amounting to a total sample of over 200,000 trips. In the first section of the paper we introduce a general discussion of inter-temporal constrained dynamic discrete choice problems and review relevant literature of transport and related fields. In the second section we describe the context of concessionary travel arrangements in London and the specific study which generated our data. The third section presents a number of alternative theoretical models of the concessionary door-to-door travel choice process, embodying different assumptions regarding the nature of the inter-temporal influences. The fourth section presents estimation results based on a sub-sample of the concessionary travel data, and discusses their significance. The final section draws some overall conclusions and discusses future research directions.
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