Comparing GPS and prompted recall data records

Global Position System (GPS) devices as a substitute for conventional travel diaries have been considered for some time but have only in the past year or so been seriously trialled as replacements. GPS devices cannot record modes of travel, trip purposes, or number of occupants in private vehicles, all of which are important attributes normally acquired in a household travel survey. This missing data is usually deduced using software processes from a combination of the GPS records, other data collected from respondents, and data available in GIS records. The level of accuracy of such software has largely been unchecked in the past. As part of an ongoing GPS-only survey in the Greater Cincinnati region, the consultant team is undertaking a web-based prompted recall survey on a subsample of households that participated in the GPS study. In this paper, we compare results from the pilot study between the processing software to the data collected from prompted recall web survey, with respect to identifying trips, mode of travel, purpose of travel, and number of household members present in a privately-owned vehicle. Overall, it was seen that prompted recall surveys are very useful in validating GPS records. These results, when collected from the entire survey (due to be completed in August 2010) will be used to develop refinements to the processing software.