Examining the Nature and Extent of the Activity-Travel Preplanning Decision Process

This paper presents results from an in-depth survey method for capturing the content and attributes of peoples' preplanned schedules. The focus is on preplanned daily activity and travel events, their typically observable attributes (event type, start and end time, location, and involved person), and the extent to which these attributes are specified and elaborated on. The survey started with an interviewer simply asking subjects to write down or discuss their schedule for the next 2 days in as much or as little detail as they knew. The interviewer subsequently probed for further details as needed. This method elicited considerable detail on decision hierarchies in the subjects' own words. Overall, it was found that activity type is the most often preplanned activity attribute, followed by location, start time, involved persons, and end time. For trips, the mode type and start time are most often planned, followed by involved persons and end time. Additional analysis further confirms that the preplanning is an ongoing decision process, wherein tentative decisions on each attribute are often made and then revisited at some point closer to execution. The implications of these findings for model development and future survey design are discussed. In particular, the results imply that activity scheduling models should adopt a nested or continuous planning loop, wherein certain activity attribute decisions are made first but are followed by subsequent stages of refinement and elaboration.