OVERVIEW

What is the activity-based approach (ABA) and how does it differ from the conventional trip-based model of travel behavior? From where has the activity approach evolved, what is its current status, and what are its potential applications in transportation forecasting and policy analysis. What have been the contributions of activity-based approaches to understanding travel behavior? The conventional trip-based model of travel demand forecasting (see chapters 2 and 3 in this volume) has always lacked a valid representation of underlying travel behavior. This model, commonly referred to as the four-step model (4SM), was developed to evaluate the impact of capital-intensive infrastructure investment projects during a period where rapid increases in transportation supply were arguably accommodating if not directing the growth in population and economic activity of the post-war boom. As long as the institutional environment and available resources supported this policy, trip-based models were sufficient to assess the relative performance of transportation alternatives. It was clear from the beginning, however, that the derived nature of the demand for transportation was understood and accepted yet not reflected in the 4SM. The 1970s, however, brought fundamental changes in urban, environmental, and energy policy, and with it the first re-consideration of travel forecasting; it was in this period that the ABA was first studied in depth. A wealth of behavioral theories, conceptual frameworks, analytical methodologies, and empirical studies o