A model of the dynamic process of time allocation to discretionary activities

This paper proposes an activity-based methodology for representing the allocation of time to discretionary activities during their programming and scheduling, based on the premise that both phases are to be consid- ered contextually and two aspects of the same decision process. The aim of this work is to extend the treatment of utility maximization associated with carrying out two activities to J activities, so as to be able to segregate the time spent traveling from the total amount of time dedicated to out-of-home activities. The global struc- ture of the model takes the form of a nested Tobit, particularly suited for reproducing a sequence of coupled choices. The first choice concerns dividing up overall discretionary time between activities inside and outside the home, then the second choice, subordinate to the first, involves rebudgeting the time between in- and out- of-home activities and trips. Thus the proposed model enables us to analyze the effects that each explicative variable exerts on trips segregated from activities outside the home and, last, during demand forecasting, the direct consequences of allocating discretionary time to trips following changes to an individual's time budget. A database created from a large-scale time-use survey (ISTAT 1988-1991) has been used for calibrating the model coefficients.