An individual based model for the allocation of time and money

This paper discusses the results of a research on the impact of limited, individual, time budgets to mobility growth. In the research the total activity pattern is analyzed. A strategic mathematical model is formulated for the allocation of time and money to activities and goods. The theoretical framework for modelling activity patterns is based on time allocation models. These models use the utility maximization approach from economics, assuming individuals to behave rationally. Individuals or households are assumed to optimize their total utility. This utility is both gained from the purchase of (consumption) goods and from the time spent on activities (to produce commodities). The model describes how individuals divide their time (24 hours a day) and money (income) over all the activities and goods. Travel is modelled as a derived demand, depending on the location of activities.

Due to the lack of combined data on time and money expenditure by complete households, the model was estimated on time use data only. The model is reduced to the allocation of time to activities at home, out-of-home, and trips to the out-of-home activity locations. The Time Budget Survey for 1980, 1985, and 1990 was used. This survey does not contain the time use data of complete households, but only for individuals (one member of each household questioned). Each respondent had to fill in a diary reporting for each quarter of an hour during a full week the main activity undertaken. The paper presents the results of the model estimation on time expenditure for different population groups.

The estimated model on time allocation is then used to explore the impacts of some extreme future scenarios. Scenarios depict possible extreme developments of independent variables, used in exploring limits in future developments of dependent variables. The paper considers extreme scenarios for population size and composition, changes in the working week (leading to changes in the time budgets for non-obligatory activities), and autonomous developments in behaviour (through time varying model parameters). The impact of these scenarios on travel time is examined. The paper shows that if average travel speed can be managed in the future, mobility growth can be limited.