Direct and indirect effects on weekend travel behaviors

The purpose of this study is to determine the causal factors that influence travel behavior. In particular, the joint relationships between trips, activities and activity durations are researched by examining the effects of personal and household attributes. In order to meet this objective, the total, direct and indirect effects of individual attributes on travel behavior are estimated using structural models. The statistical assumption and the interpretations of coefficients in classical causal analysis are similar to those in linear regression models. Specifically, the direct effects, as estimated coefficients, are only offered and interpreted. However, in travel behavior that results from complicated relationships among trips, activities and individual attributes, the indirect effects among factors related to travel behavior cannot be disregarded. The indirect effects through other intervening factors, in addition to the direct effects, may cause the total effect of specified factors on travel behavior. If only the direct effect is considered for analysis, the causal relationships among factors may not be able to be adequately understood. The advantage of using structural models is that they are able to estimate, in addition to direct structural effects, the indirect effects through other intervening factors. The study also assumes that Saturday travel behavior has an effect on Sunday travel behavior. The subdivided indirect effects of the personal and household attributes on trip generation, activity frequency, and activity durations are empirically analyzed in detail.