Based on a review of literature on trip underreporting in regional household travel surveys and the
development of associated correction factors, most trip under-reporting is associated with households that
own 3 or more vehicles, households with incomes of less than $50,000, and respondents under the age of
25. From a travel behavior perspective, respondents who travel substantially make several short trips
(less than 5 minutes), and make trips of a discretionary nature are most likely to “forget” to record this
travel (as has been suggested on parallel literature regarding trip-chaining).
The studies to date have clearly aided in identifying factors associated with trip under-reporting in
regional travel surveys. In this paper we contribute to this existing literature and continuing discussion
regarding GPS technology in travel surveys in several ways. First, in the current study (and unlike earlier
studies), we model both the presence of trip under-reporting by an individual as well as the level of trip
under-reporting by the individual. The separation of the presence of trip under-reporting from the level of
trip under-reporting recognizes that different explanatory variables may affect these outcomes and/or that
the same explanatory variable may affect these outcomes differently. Second, the joint model also
recognizes that the likelihood of trip under-reporting and the level of trip under-reporting may be related
to one another. For example, it is conceivable (if not very likely) that individuals who are, by nature, less
likely to be responsive to surveys are the ones who under-report and under-report substantially.
Similarly, individuals who are, by nature, very interested in the survey would be the ones less likely to
under-report at all, and even if they did under-report, will do so only marginally. Third, in addition to
jointly modeling trip under-reporting and the level of trip under-reporting, the empirical analysis in the
current study considers a comprehensive set of variables related to driver demographics, driver travel
characteristics, and driver adherence to survey protocol. Finally, we translate our empirical analysis
results to recommendations regarding household travel survey procedures to reduce the magnitude of trip
under-reporting in future travel surveys conducting using the traditional approach.