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36 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 1 determinations are the use of a travel diary and working activity, and the mode of transportation used to travel to in residential land use, while the least important deter- and from the activity. The participation of other individ- minates are being a male and traveling long distances. uals in the activity and travel represents still another The model results can be used to identify possible facet included in activity-based models. More robust approaches to address the underreporting by various activity-based models also incorporate learning effects groups. Providing a clear definition of what to record and other advanced elements. may address individuals working in residential land use. Activity-based models require more sophisticated Providing travelers with high trip rates with more room and more detailed data than the traditional travel mod- to record trips on the forms may help. These individuals els. To accommodate the calibration and validation data should be identified during recruitment. Probing for trips requirements of dynamic activity-based models, more during lunch and stops along the way should be per- detailed activity-travel diary information is needed. formed for unemployed individuals in the same way as Travel diaries consist of a sequence of activities and jour- for workers. neys completed by each individual in a household. The The model results indicate a need to better engage diaries focus on all the activities and journeys completed drivers under the age of 30 in the surveys, as well as indi- by an individual. Completing activity-travel diaries viduals with high school educations. More challenging is requires a lot of effort on the part of the respondent. addressing the underreporting of the proxy-reported Travel diaries take time to fill out and require individu- travel. Not allowing proxy reporting has significant cost als to remember and record numerous activities. implications and may introduce more bias into the sur- A number of methods have been used to collect vey data than that introduced by allowing proxy report- travel-diary information over the years. The basic paper- ing. Strengthening the telephone interview may help and-pencil method is still used in many areas. Advan- address this issue, as well as those related to unemployed tages to this approach are that the diaries can be filled individuals. out at any time and place and are relatively easy to com- plete. This method can be prone to errors and inconsis- tencies, however. It can also be complex and tedious for DYNAMIC ACTIVITY-TRAVEL DIARY DATA some individuals. COLLECTION USING A GLOBAL POSITIONING A second approach is using computer-aided self- SYSTEMENABLED PERSONAL interviews to record activity-travel scheduling behavior. DIGITAL ASSISTANT The Computerized Household Activity Scheduling Elici- tor (CHASE) provides an example of this approach. This Bruno Kochan, Tom Bellemans, Davy Janssens, method includes a multiday computerized scheduling and Geert Wets interface, which allows individuals to record their sched- uling decisions by adding, modifying, and deleting activi- Davy Janssens described the use of a GPS-enabled PDA ties to their schedule. Possible advantages to this method device to improve travel diary data collection efforts with include the ability to obtain more detailed information activity-based travel models. He discussed data collec- and improved data quality. Potential limitations include tion needs with activity-based travel models, available the need to access a computer at specific places and times. computerized travel survey data collection tools, the A third approach is using Internet-based travel advantages and limitations of different approaches, and diaries. This method provides greater flexibility for the a new GPS-enabled activity-travel diary data collection individual, because the diaries can be completed at dif- tool. Volume 2 contains a paper on this topic.3 The fol- ferent locations that have Internet access and at times lowing points were covered in his presentation. that are convenient to the participant. A possible limita- tion with this approach is the need for participants to The traditional four-step models were developed in have Internet access. the 1950s to predict travel demand for different trans- Building on these efforts, research in Belgium is portation options. Recently, activity-based models have focusing on the development and application of an inte- been developed to address some of the limitations asso- grated travel diary approach using GPS in a PDA appli- ciated with four-step models. Activity-based models pre- cation. This approach involves a participant recording dict interdependencies between several facets of activity their planned activities in a PDA and collecting informa- profiles. These facets include the type of activity, when tion on the participant's actual activities through the use and where the activity is conducted, the duration of the of GPS. The planned and actual activities can be com- pared and additional information concerning differences 3See Kochan, B., T. Bellemans, D. Janssens, and G. Wets. Dynamic can be gathered as needed. Activity-Travel Diary Data Collection Using a Global Positioning A number of advantages may be realized through SystemEnabled Personal Digital Assistant. Volume 2, pp. 9497. the use of a GPS-enabled PDA travel survey. First, trip