This study proposes a household activity-based network equilibrium model to investigate the effects of intra-household interactions on the joint activity-travel choices of household members in congested road networks.

In contrast to typical activity-travel choice models in which individuals make selfish choices to maximize their own utility, the proposed model is based on a new household optimum utility approach that simultaneously takes into account the choices of all individuals in the same household to maximize their household utility.

The household utility includes the marginal utilities of performing activities, cost of travel by mode, and extra utilities for joint activities and travel of household members. Two new household-oriented network equilibrium principles; namely, household optimum (HO) and household-based system optimum (HSO), are introduced together with the formulations of their equivalent mathematical programming problems. The analytical relationships between HO, HSO, conventional user equilibrium, and individual-based system optimum are then investigated.

To avoid the need for pre-specifying the choice set in advance, the daily activity-travel choices of household members and their interactions are modeled as a joint-activity-travel path choice in a joint-activity-time-space supernetwork platform. The proposed model is formulated as an equivalent variational inequality problem and solved by a diagonalization method. Numerical examples are provided to illustrate the merits of the proposed model together with the key insights from the results.

The proposed model can coherently assess the effects of various transport policies on congested road networks with high-occupancy toll lanes for long-term strategic planning.

William H.K. Lam is a Chair Professor of Civil & Transportation Engineering and has been the Head of the Civil & Environmental Engineering Department, The Hong Kong Polytechnic University from 2013 to 2019.  He is also an Honorary Professor at the Institute for Transport and Logistics Studies, The University of Sydney, Australia since 2015. Professor Lam has over 35-year professional experience in research and practice for planning and design of transport infrastructures. He is the founding Editor-in-Chief of the SCI Journal – Transportmetrica and is now one of the Co-Editors-in-Chief of Transportmetrica A: Transport Science.  He is also the Convenor of the International Advisory Committee of the International Symposium on Transportation and Traffic Theory. He has been the President of the Hong Kong Society for Transportation Studies from 1996 to 2019. Professor Lam is the author of more than 300 Web of Science journal and conference proceedings papers together with 70 consultancy reports. His research interests include transport network modeling and infrastructure planning, travel demand forecasts and risk assessment, ITS technology and planning, public transport and pedestrian studies.