Exploring the Use of Passive GPS Devices to Measure Travel

Abstract

A persistent problem in household travel surveys (HTS) is the inability of subjects to provide accurate geographic information about their origins and destinations, and accurate, objective data about trip times and distances. Most people know their home address. Many workers know their workplace address; few parents or children know their school addresses. Few, if any, can provide the street address of the places where they shop, and many will not know the street address of friends and relatives that they visit in the local area. Other addresses, e.g., for churches, restaurants, banks, are not known. This results in lengthy and costly geocoding that still leaves 10 to 20 percent of trip ends uncoded, with a consequent loss of the data. Other addresses may be coded imprecisely, because it cannot be determined on which side of a street or intersection the visited location is sited. People report perceived travel times and distances. The content of the time, e.g., travelling in heavily congested conditions, riding on an overcrowded bus, or travelling with a friend, leads to major differences in perception and reporting of travel time. Negative content of time leads to overestimates of time and distance, while positive content leads to underestimates. In addition, depending on the nature of the survey, people may intentionally misreport times or distances to justify some perceived value judgement in the survey. Most transport planners would like to collect route-choice data. However, those that have attempted this task have almost invariably failed. A few surveys have been able to determine freeway use on a trip. The lack of empirical data on route choice is one reason that most commonly used assignment procedures are based on the incorrect paradigm of minimising travel time. Recently, GIS applications in transport have enabled attempts to deal with the problem of unknown trip-end addresses by equipping interviewers with computerised gazetteers. These allow them to probe subjects intelligently about the locations of trip starts and ends. However, the up-front costs of compiling such a gazetteer are large compared to the data-collection task. This method has had only limited success in dealing with the geographic location issue. It does not deal with the issues of accurate times, distances, or routes.