XCARCITY - Designing car-low urban areas using digital twins Increasing housing density and decreasing space for transport infrastructure and private parking are posing severe challenges for the sustainable accessibility of urban regions. There is an urgent need for space-efficient smart mobility solutions that do not depend on the single use and possession of a private car, such as flexible combinations of walking and cycling, shared electric vehicles, transport hubs, freight delivery and traffic management. However, it is highly uncertain whether these solutions can indeed provide sufficient levels of sustainable accessibility. Empirical data about the use and impacts of smart mobility is scarce and ex-ante modelling tools are lacking solid behavioral assumptions about the use of smart mobility. The research program XCARCITY.nl will develop a federation of digital twins that will support stakeholders in collaborative decision making for the planning and operation of smart mobility services. The digital twins will support both planning and operation using a feedback-control loop in which real-life and virtual reality data are combined with model-based scenario development and implementation of interventions. Scientific challenges to be addressed are (1) measuring the behavior of individuals and flows while respecting privacy and security, (2) developing smart mobility services that meet travel demands and (3) assessing the contribution of smart mobility to sustainable and inclusive accessibility. The XCARCITY digital twins will enable public authorities, area developers and mobility providers to successfully cooperate toward sustainable accessibility of car-low urban regions. This special session aims to explore and discuss how digital twins can be used to co-design car-low urban areas. In the first part of this session, we will apply a digital twin called Urban Strategy to co-design a car-low area in Amsterdam with all the participants. We will start with having a discussion on objectives (e.g., improving accessibility, livability, and equity), indicators and interventions that can be taken. The digital twin will be used to apply the most relevant interventions, assess the impacts of the design, and adjust the design again. In the second part of this session, we will have a structured discussion with the participants on how 3D Amsterdam and a data-driven digital twin called the Outdoor Mobility Digital Twin can be used in combination with Urban Strategy to study behavioral responses to car-restrictive and smart mobility interventions and to assess the impacts of those interventions. The session will be organized by TU Delft, TNO, the municipality of Amsterdam and AMS.