This study addresses the day-to-day variation of three key aspects of the home-to-work commute: (1) the time of departure from home; (2) the frequency, purpose, and duration of intervening stops between home and work; and (3) the path actually followed through the network. It is based on detailed two-week diaries of actual commuting trips completed by a sample of auto commuters in Austin, Texas. The paper examines alternative definitions and measures of variability in the context of the daily commute by comparing a "day-to-day" approach to a "deviation-from-usual" approach for defining individual switching behaviour. Models are developed to relate observed trip-chaining, route, and departure-time switching patterns to the commuters' characteristics, such as workplace conditions, socioeconomic attributes, and network-performance characteristics. In addition, this study provides valuable confirmation of insights previously suggested in stated-preference laboratory experiments involving actual commuters in a simulated traffic system. About 25 percent of all reported commutes contained at least one non-work stop, underscoring the importance of trip-linking in commuting behaviour. These multipurpose trips are shown to influence significantly the departure time and route-switching behaviour of commuters. In general, commuters change departure times more frequently than routes, confirming previous results from laboratory experiments. (A)
Abstract