Group Behavior Modeling

Even though research on group behavior is still a comparatively new field in transportation, rapid progress has been made since the beginning of the 21st century. Up to now, a multiple-member household has been primarily considered as a decision-making unit under the principle of utility maximization with multi-linear and iso-elastic household utility functions to represent intra-household interactions in household task and time allocation, joint activity participation and ride-sharing, car ownership and residential choice behavior, etc. A few exceptions have been observed to use a rule-based approach. The workshop on "Group Behavior" invited five papers, including the resource paper by Harry Timmermans, who gave a comprehensive review of existing studies and discussed unsolved research issues at the time of writing. The five papers introduced group behavior modeling in Japan, new modeling developments in the context of household timing decision behavior, social network, and pro-social behavior in network. However existing studies have mainly focused on decision outcomes rather than the processes. Further developments, however, might explore more inter-personal interactions with respect to multi-faceted behavior aspects, reflecting the need to bring more consistency in predicting travelers' genuine responses under policy interventions, from both modeling and survey perspectives. It is worth representing context and situation effects as well as temporal effects (e.g., day-to-day dynamics and learning). Group decision theories from other fields could be helpful; for example, game theory could serve as a promising tool but more empirical studies are required. The stated choice approach should be applied to investigate the process of negotiation among decision makers. As a whole, further efforts in both modeling and survey are required to explore the behavior of more general group units in transportation.