Investigation of alternative methods for modeling joint activity participation

This study represents a research effort to capture explicitly the intrahousehold interactions involved in the decision to participate in a joint activity. Joint activity participation is a lesser-explored step in activitybased travel demand modeling, since enlisting all possible subsets of household members in a large household results in many alternatives. For example, the number of possible subsets of members out of 10 persons is 2¹⁰ = 1,024. After the exclusion of one empty subset and 10 subsets with a single member, 1,013 distinct subsets should be considered with two or more members for joint activity participation. Even more important, a joint choice model formulation is behaviorally unappealing and would require the formulation of a complicated utility function for each possible subset. Additionally, different subsets would have a highly different degree of similarity that would require a sophisticated error structure. This paper analyzes three methods to model joint activity participation that are relatively easy to estimate and implement for households of any size. In all three methods, the travel party is constructed on the basis of the individual and pairwise propensities of the household members to be engaged in a joint activity. These propensities are statistically estimated on survey data in the form of relatively simple binary choice models. The travel party emerges in the process of microsimulation as a result of the reconciliation of the decisions of different household members. This approach is an example of the use of the agent-based modeling paradigm to frame an intrahousehold decision-making mechanism in addition to econometric models.