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activity- travel diary data collection system (e.g., CHASE), a mobile system does not restrict the location for data collection and is easy for the survey respondents to carry for in- situation data input. Moreover, as the PDA is equipped with a GPS receiver, GPS data can be collected as well. The system conceptually consists of two graphical user interfaces (GUIs), household survey and activity- based survey; a GPS logger; a data structure (activity diary and both household and GPS data); a data quality control module (data integrity checks); a trip identifica- tion module; a GIS module; and a communication mod- ule (Figure 1). The modular structure of the application allows for customization. The implementation of mod- ules less important for the current research can be omitted. The GPS logger is used to trace the physical travel paths and the travel times. If the GPS logger is active, it receives the GPS data from the GPS chip and stores it by using the GPS data module. The GPS logger collects data continuously, and therefore it needs to operate in the background. This automatic feature has two advantages. First, it facilitates data capturing, and, second, although the survey respondent may forget to register a new activ- ity, the GPS logger captures the userâs position during the travel period. In this way, the system can prevent the loss of activity- travel data. Indeed, once the system detects a change in location that is not reported as travel by the survey respondent, it prompts the respondent for addi- tional information. The GPS data, stored in the GPS data module, can also be used for trip identification. Once the performed trip is identified, it can be used to verify whether the information about activities reported by the respondent is consistent with the actually recorded trip. If there are inconsistencies, the respondent will be prompted for clarification. The household survey GUI inquires for personal demographic and activityâ travel- related information. These data are collected at the beginning of the survey period and stored in the activity diary and household data module. During the survey period, the respondent interacts frequently with the activity- based survey GUI, which is the major interface of the application. This GUI is used to register the activity- travel diary data during the survey period. It is used to enter, to modify, or to delete an activ- ity or a trip, but it is also triggered if the data integrity checks module detects an inconsistency (e.g., a city name that does not exist) and the activity diary data need to be altered. The information stored in the handheld devices can be downloaded through the communication module. Depending on the implementation of the communication module and the available hardware, the data can be col- lected and stored on a data server either during or after the survey period. The spatial dimension (the âwhereâ facet) is the most difficult item to collect in traditional paper- and- pencil diaries. People often do not precisely recall the exact location or the name of the street where a particular activity occurred. Hence, traditional diaries are often restricted by limitations to the details of information col- lected. The computer- assisted data collection tools can make a significant contribution here by integrating a GIS module, which enables the user to either pinpoint a loca- tion on a map or to enter a location manually. Computer- assisted data collection tools allow for data quality control. Indeed, a computer system can check for anomalies and prompt the respondent for additional information. Entries that report activities with a start hour of an activity later than the end hour, activity locations that do not exist, and many others are detected by the data integrity checks module of the PDA application. CONCLUSION In this paper, a data collection tool that is able to capture dynamic activity- travel scheduling behavior was pre- sented. The detailed data collected by this tool will be used to develop a dynamic activity- based transport model. In the functional description of the application, a modular approach toward a general data collection application was presented. Next, the importance of each of these modules was described. Currently, the presented data collection tool is deployed in a large- scale activity- travel survey in Flanders, Belgium. 96 INNOVATIONS IN TRAVEL DEMAND MODELING, VOLUME 2 GPS Data Activity Diary and Household Data GUI Household Survey GUI Activity-Based Survey GPS Logger GIS Module Communication Module Trip Identification Data Integrity Checks FIGURE 1 Schematic representation of functional descrip- tion modules composing collection tool for activity-travel diary data.
