This research examines the use of individualized marketing as a transportation demand management (TDM) strategy, using the City of Portland's SmartTrips program. This research project has two specific aims: (1) to evaluate whether the benefits of these individualized marketing programs continue to at least one year after the project ends; and (2) to examine whether the theory of planned behavior (TPB) can help explain the behavior changes identified. Surveys of residents conducted one or two years after the original program found that the share of daily trips made driving alone, walking, and bicycling were comparable to that found in the previous follow-up surveys, still significantly lower (for driving alone) or higher (for walking and bicycling) than the pre-surveys. This may indicate that the SmartTrips program was effective at changing behavior for a longer time period than previously measured. The theory of planned behavior (TPB) models were effective at explaining travel behavior. The models showed that attitudes, social norms, and perceived behavioral control explain a large share (45-55%) of the variance in travel behavior. The relative influence of each component of the model differed some by mode. The findings support previous research that individualized marketing programs can be effective at changing people?s travel behavior. The findings indicate that the benefits of the programs may extend beyond one year and up to at least two years. However, the research also found that the programs may not be as effective in environments that are less conducive to walking, bicycling, and transit. The research also found that that attitudes, norms, and perceptions play a large role in travel decisions. To be most effective, individualized marketing programs need to influence these factors, though efforts that focus on social norms to influence travel behavior may be less effective than those that include attitudinal and behavioral control components. Sensitivity to regional characteristics and the specific travel mode that is the target of interest is also warranted.