Results and Implications for Survey Methods.
The results from our modeling effort provide important insights regarding under-reporting tendencies in
traditional household travel surveys. First, the underlying mechanism that represents whether an
individuals under-reports or not is different from the mechanism that determines the level of underreporting.
At the same time, there are common unobserved factors that influence both the under-reporting
propensity and the propensity associated with the level of under-reporting. Consequently, it is important
to use the joint binary-unordered response framework of the current study to analyze trip under-reporting
and its magnitude. Second, the effect of driver demographics indicates that young adults (less than 30
years of age), men, individuals with less than high school education, unemployed individuals, individuals
working in clerical and manufacturing professions, workers employed at residential, industrial, and
medical land-uses, and individuals in nuclear families are all more likely to under-report trips in
household travel surveys than other respondents. Third, driver travel characteristics that affect the
tendency to under-report include making a high number of trips on the survey day, traveling long
distances per trip, and trip chaining. Fourth, drivers who do not use the travel diary to record their travel
are more likely to miss trips than those who use the travel diary, and proxy-reporting leads to more
missed trips