Intra-household Interactions in tour-based mode choice: The role of social, temporal, spatial and resource constraints

• Develop a mode choice model incorporating joint household travel and apply the model to simulate the effect of transport policies on modal shift.
• Explore the role of various constraints on joint household travel.
• Conduct a parallel analysis comparing joint and individual household travel analysis.
• Show that a joint household travel analysis does not necessarily identify a lower modal shift for policy outcomes as compared to individual analysis.
• Establish the conditions under which models without joint travel overestimates or underestimates travellers’ responses to transport policy.

Under social, temporal, spatial and resource constraints, household members interact and search for ways to fulfil household and individual needs, one of which is travelling together. Understanding the motivation for joint household travel and its effect on an individual’s mode choices is critical to the formulation of transport policies and planning practices for sustainable transport choices. This paper examines individuals’ mode choices with joint household travel being explicitly incorporated within a nested logit model using the Sydney Household Travel Survey data and a typology of tours that captures various patterns of household interactions. The results indicate that joint travel is influenced by household resources, social and mobility constraints, activity types, and the land use patterns at both origin and destination. Also, mode choices differ significantly across joint tour patterns with public transport being less likely to be used for joint travel. Scenario analysis shows that individual tours contribute the most while complex joint tours contribute least to modal shifts from car to public transport which results from changes to transport policies and the level of services. Contrary to suggestions in the literature, a joint household (as compared to individual) travel analysis does not necessarily identify a lower modal shift for policy outcomes.