THE USEFULNESS OF TRAVEL BUDGETS. IN: URBAN TRANSPORT

Many researchers have found the idea of a constant outlay on travel a magnetic hypothesis. If true, it would provide a useful touchstone to test the reliability of existing transport models and a constraint to improve them. This paper has five parts. First, a number of ways are investigated in which a known travel budget could be incorporated into the generation, mode choice, or distribution parts of current models. Secondly, there is a discussion of some implications of doing this on policy evaluation. Thirdly, consideration is given to some of the difficulties in interpreting empirical work on this subject, to judge whether inferences that have been drawn on stability of travel budgets are supported. Fourthly. Some theoretical problems are raised, particularly relating to the behavioral implications of stable budget assumptions. Lastly, some general conclusions are drawn. It is suggested that we are likely to learn most about travel behavior, mobility and the effect of alternative policies if the time and money allocated to travel are treated as variables and not behavioral constants. These outlays are likely to be influenced in particular by travel opportunities and costs, as well as various socio-economic and personal characteristics.