An Activity Scheduling Process Approach to Understanding Travel Behavior

The need to understand and forecast individual travel behavior over longer periods of time and space has placed tremendous stress on available data collection and modelling techniques. Traditional travel survey methods tend to focus exclusively on observed choices, using diary and stated preference techniques. However, improving our understanding requires more than just an improved accounting of observing outcomes – rather, travel behavior researchers are increasingly recognizing the need to improve our understanding of the decision processes that underlying observed outcomes. This paper is concerned with outlining a new approach to understanding travel behavior that intrinsically recognizes that observed travel patterns are really the result of unobserved and underlying activity scheduling decision process. This approach represents an important extension of the space-time prism paradigm, and is meant to address recent policy assessment and modelling needs related to the shift towards transportation demand management. Empirical evidence gathered through the use of a new computerized household activity scheduling survey is used to describe the fundamentals of this process. In particular, evidence presented in this paper demonstrates that activity scheduling is a highly dynamic process occurring over many time horizons, with significant levels of revisions and continued pre-planning during schedule execution. This represents a significant challenge to past modelling assumptions that activities are planned simultaneously, or that they are planned and executed in the same sequence. The paper concludes with a discussion on modelling implications and future directions. Overall, this paper is meant to challenge planners, researchers and modellers to think more deeply about underlying decision processes and the assumptions inherent in their models.