Evaluation of travel demand management (TDM) programs is important to their success, in that it helps policy makers establish proper approaches toward policy implementation. A study attempted to assess the effectiveness of the Weekly No-Driving Day program in Seoul, South Korea, an ongoing attempt to reduce car use. Volunteer participants select days on which to refrain from car use. For the assessment, a field survey to investigate compliance rates, that is, assessing whether 6,000 vehicles or less are driven daily, was designed; at the same time, a questionnaire-based survey was conducted to determine which drivers are more likely to participate in the program. Results of the field survey suggested that daily car use was reduced by 1.3% in the Seoul area. Although this outcome seems insignificant, it is significant in that the program is voluntary and is implemented over the whole metropolitan area, with more than 2 million vehicles targeted. However, the questionnaire-based survey indicated that car-dependent drivers, who spend more time driving and operating vehicles on a regular basis, are less likely than others to participate in the program. A concern is that success could be significantly diminished if those car-dependent citizens were not encouraged to participate in the program. It is anticipated that findings from this study will contribute to improved development and implementation of future TDM programs.