Many cities are implementing car-reducing measures to achieve goals related to livability, such as climate change reduction, air quality improvements, improved living space, improved health and safety and reduced costs. Policies at the local, national, and supranational levels affect the measures that cities can take. This thesis addresses the challenges cities face in implementing car-reducing policies. Achieving the goals for which local governments are implementing car-reducing policies requires transformational adaptation. This system-wide radical change increases a system’s ability to deal with future uncertainty. However, it is challenging for policymakers to destabilize existing regimes. Answering governance questions related to context, power, resources, and legitimacy can help fill the research gap regarding real-world policy examples and aid in the transition towards sustainable mobility. This thesis proposes a framework based on theory and practice to address the challenges that policymakers may face in policy implementation. The main research question is: What success factors and barriers in the implementation of car-reducing measures are present in European cities, and what are the implications for European cities of the scale of Amsterdam? Amsterdam is the reference case selected to contextualise the results of this thesis. Case studies in cities with comparable population sizes, namely Copenhagen, Barcelona, Bremen, and Milan, with considerable experience in car-reducing measures, provide new insights for policymaking. Understanding the context in which a policy operates has shown to be essential in its success and/or failure. The main barriers in the implementation are explored with stakeholders involved in policymaking. Eight different success factors have been identified to overcome the barriers and successfully implement their policies. Six originate from the literature and were confirmed in the interviews. The two final success factors of ‘the inarguability of schools’ and ‘the undeniability of hard evidence’, emerged during the interviews. These stakeholders identified the links between these factors and barriers, and how the success factors can reduce the barriers. The success factors of ‘showing openness and flexibility’ and ‘pilots/trials to create legitimacy’ can lower most barriers. Combined, these success factors can influence all barriers and are, therefore, most important. The analysis of the case studies and the comparison with the literature results in lessons for cities looking to implement car-reducing policies. An in-depth analysis is performed for Amsterdam. Three main lessons of the studied cases stand out for Amsterdam. For other cities looking to implement car-reducing policies, four general lessons have been determined: 1. Continuously explore new possibilities for policymaking. 2. Be aware of the context and stakeholders’ needs to select appropriate measures and adjust them according to the context. 3. Create and identify windows of opportunity and be ready when that window opens. 4. Test new measures before implementing them permanently to select the optimal location and collect data on the measure’s impact. The proposed framework of success factors and barriers can be used by policymakers to address the challenges they face in implementation. Using the framework and the lessons during the design of their policies, may significantly reduce the barriers they face and ensure successful implementation.