Travel not only serves the purpose of engaging in spatially separated activities but also fulfills fundamental human needs for self-actualization, independence, and a sense of connection with the world. Unfortunately, the transportation sector faces significant challenges related to environmental, economic, and social issues, largely attributed to privately owned cars. Cars contribute to environmental problems through, e.g., emissions, resource depletion, and noise pollution, while also imposing economic burdens and exacerbating social inequalities. Despite these challenges, private car ownership and usage remain dominant. Addressing these issues calls for a transition to a sustainable and equitable mobility system. Currently, the predominant approach is the efficiency strategy, which focuses on technological advancements to reduce resource consumption. However, this strategy alone falls short, as the success of technological innovations ultimately depends on human behavior. Adaptations in behavior may offset efficiency gains, and improved technologies may not fully consider the true motivations, habits, and needs of mobility users. Consequently, the sufficiency strategy becomes indispensable, centering on human decision-making, lifestyles, behaviors, and consumption patterns.This dissertation aims to contribute to the development of a sustainable transportation system by identifying and laying the groundwork for effective, psychology-based approaches. Four individual studies delve into different aspects of the sufficiency strategy. Study 1. First, it is important to recognize that individuals exhibit a wide array of diverse needs, physical abilities, attitudes, and available mobility options. This study embarked on the task of identifying distinct mobility types prevalent among the German population. Drawing data from a representative national survey on everyday mobility behavior, socio-demographic, behavioral, geographic, and psychographic information was used to cluster individuals into eight stable mobility profiles by means of exploratory factor and cluster analysis. The results provide a foundation for the development of customized interventions aimed at reducing private car use and fostering sustainable transportation choices that accommodate diverse needs and preferences. Study 2. In the realm of novel mobility solutions tailored to address these needs, a qualitative, focus-group based study was conducted in Berlin, Germany, to explore the potential of Mobility as a Service (MaaS) in redirecting users away from private cars and enhancing access to diverse transportation options. Data from 12 focus group sessions was analyzed using qualitative content analysis. Results revealed that while MaaS effectively addresses nearly all instrumental motives of private car use, it falls short in tackling the symbolic and affective motives associated with car ownership. However, MaaS may contribute to a more sustainable mobility system by emphasizing its unique symbolic and affective motives as well as highlighting its potential to alleviate the burdens of car ownership. Study 3. As a readily applicable intervention, this study comprised an experiment to assess the effectiveness of nudges in encouraging commuters to shift toward transit options, employing the theory of planned behavior as a theoretical foundation. Participants were randomly assigned to different nudging groups or a control group, and data was analyzed using structural equation modeling and logistic regressions. While the theory demonstrated a good prediction of individuals’ decisions, none of the nudges achieved statistically significant effectiveness. This exploration of nudging interventions in the transportation sector provides insights into the limitations of strategies aimed at changing habituated commuting behavior. Study 4. The Covid-19 pandemic presented an unprecedented disruption to commuting habits, offering a unique opportunity to examine the impact of telecommuting on mobility-related attitudes. Through factor analysis and multivariate analyses of variance on longitudinal data from the California panel study of emerging transportation, the development of mobility-related attitudes of telecommuters and physical commuters was compared. Further, individuals’ intentions to telecommute in the future were modeled using external job related and attitudinal predictors. Results showed that fundamental attitudes toward mobility remained largely stable despitethe variations in commuting behavior and the pandemic’s progression. The main determinants of intentions to telecommute in the future were not job related but internal, including attitudes and tech-savviness. The model further suggests a prevalence of hybrid working beyond the pandemic, potentially opening up opportunities to prioritize sustainable transportation options due to a reduced demand for daily commuting. In addition to examining these four research projects individually, findings and their broader implications that span across the studies are discussed. These include the increasingly important role of tech-savviness, the integration of attitudinal constructs in interdisciplinary transportation research, the questionable impact of environmental concern on behavior, and the ambiguous effects of nudging interventions in the transportation sector. By delving into various psychological aspects of individuals' mobility behavior, this dissertation highlights the potential and, at times, the shortcomings of a diverse range of measures aimed at addressing the challenges of the transportation sector in the pursuit of sustainability and equity.