Developing Better Probes. Based on the findings of the earlier GPS studies, it has become
standard procedure to probe workers about potential stops made during their commutes. In addition, as a
form of validation, respondents who report no travel are subjected to a series of questions to confirm the
legitimacy of the reporting. The results of this study suggest that additional probes as part of the travel
retrieval interview may be warranted for all travelers, not just workers or those who report no travel.
Specifically, this study indicates that there is a high propensity to under-report travel if the driver is
unemployed, has his/her travel data reported by proxy, or travels long distances. The finding that
unemployed drivers have a higher tendency to under-report trips is a new correlate to be considered. In
the past, the modeling focus on the work trip (and how discretionary travel may be incorporated into the
work commute) has led to an emphasis on collecting travel/activities that occur during the lunch break or
during the commute to/from the workplace. Drivers who are unemployed do not receive similar levels of
scrutiny or probes, but should according to the findings of this study.