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