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D Y N A M I C A C T I V I T Y- T R AV E L D I A RY D ATA C O L L E C T I O N 95 GPS-enabled PDA are discussed. Following that, the ADVANTAGES AND DISADVANTAGES OF functional description of the data collection tool receives A GPS-ENABLED PDA further consideration, with the final section presenting conclusions. In the past, desktop computerassisted data collection tools were used for completing scheduling surveys; this process provided activity-travel diary data. However, STATE OF THE ART IN COMPUTERIZED these systems are not able to trace the actual activity- ACTIVITY-TRAVEL DATA COLLECTION TOOLS travel execution due to their mobility constraints. To solve this problem, one might think of a PDA with GPS CHASE (Computerized Household Activity Scheduling technology for enhancing the data collection tool's Elicitor) was the first computer-aided self-interview of mobility. The potential advantages of using a PDA with activity scheduling behavior (Doherty and Miller 2000). GPS to supplement travel survey data collection are The purpose was to work out a survey that was able to numerous: (a) when using a desktop computerassisted track down the preceding scheduling process that data collection tool, the respondents have to remember resulted in the definitive execution of an individual's the exact locations of their start and end positions schedule, along with the observed activity-travel patterns whereas, with a PDA with GPS, trip origin, destination, as the outcome. In the past, traditional survey techniques and route data are automatically collected without bur- that use diaries (e.g., paper-and-pencil techniques) were dening the respondent; (b) as the respondent may forget limited almost exclusively to observed patterns, provid- to report an activity trip, another advantage exists in ing little insight into decision processes. This shortcom- recovery of unreported trips, as all routes are recorded; ing was dealt with through the development of a (c) accurate trip start and end times are automatically multiday computerized scheduling interface. The users' determined, as well as trip lengths; (d) the GPS data can task consisted of keeping track of their scheduling deci- be used to verify reported data; (e) both the data entry sions by adding, modifying, and deleting activities to cost and the cost of postprocessing the data constitute a their schedule as they occurred during a multiday period. significant share of the total data collection cost (Zhou The application made notes of each of these scheduling 2003). These costs can be reduced to a minimum with decisions, along with prompting for additional informa- computer-assisted forms of data collection. tion (e.g., the reasons for these decisions, the exact tim- One of the most important shortcomings of GPS tech- ing of these decisions). The prompting process was nology is that the system is not always reliable during the extremely complex with paper-and-pencil techniques. entire trip-recording period. Indeed, civilian GPS Initial testing results indicated that this computerized receivers have potential position errors resulting from, approach revealed a considerable amount of informa- for example, multipath, selective availability, and the tion on the scheduling process and observed patterns, like. However, by combining the GPS data with other while minimizing respondent burden (Doherty and data sources such as location information reported by Miller 2000). Many adjustments and sophistications of the respondent and GIS maps, these errors can generally this method have followed the original approach, includ- be overcome. Another issue associated with the use of a ing applications on the Internet (Lee et al. 2000), devel- handheld device is the storage capacity available to save opment of a geographical information system (GIS) the collected data. However, with ever-decreasing stor- interface for location and route tracking (Kreitz and age capacity prices, PDAs can readily be fitted with suf- Doherty 2002), and integration of GPS in a PDA appli- ficient memory to conduct the surveys at a reasonable cation (Doherty et al. 2001). price. As a PDA is powered by a battery, it has to be In contributing to this line of research, the authors recharged regularly, an extra burden for the respondent. suggest an application that runs on a GPS-enabled PDA. To reduce the number of times the PDA needs to be Several key development issues are desire (a) to capture recharged, an energy-conserving battery management the dynamic activity-travel scheduling processes, (b) to system was integrated into the data collection applica- reduce respondent burden, and (c) to improve activity- tion. This way the autonomy of the data collection tool travel data quality. can be significantly improved. The application described in this paper captures the process of dynamic activity-travel scheduling by collect- ing first information on the activities the respondent FUNCTIONAL DESCRIPTION OF GPS-ENABLED plans to execute and then information on the activities ACTIVITY-TRAVEL DIARY DATA that the respondent did execute (diary) afterwards. COLLECTION TOOL Next, the planning and the diary are compared, and additional information about the differences is gathered The central theme of the data collection tool revolves if required. around a PDA. Compared with a typical computerized