Introduction: To reduce pollution from motorized private cars, a modal shift toward more sustainable modes, such as public transport, is desired. A first step to achieving this is the subscription to a public transport ticket. It was investigated if an extended version of the theory of planned behavior is suited to predict subscription to a public transport ticket, and if environmental concern—the channel through which many sustainable transport modes are advertised—plays a significant role. It was further examined if nudging serves as an effective measure in convincing employees to subscribe to the offered ticket. Nudges encourage desired behaviors by changing the information set that individuals face when taking decisions; in this paper, this includes favorable defaults and the manipulation of the social norm. Since nudges lack a coherent theory, it was tested if these nudges can be integrated into the aforementioned theory. Method: By means of an online experiment, participants (N = 373) were randomly assigned to different nudging conditions or a control condition. The questionnaire mimicked a working contract, including the decision for or against a subscription to the ticket. Results: Results of structural equation modeling revealed that the theory predicted the purchase decision well, yet the impact of environmental concern was surprisingly low. Most tickets were purchased in the default condition, but no nudge reached statistical significance. Discussion and Conclusion: The limitations of nudging in the transport sector are discussed, along with the effectiveness of advertising public transport through an environmental lens.