Across Europe, cities are attempting to radically reduce their reliance on car-based mobility in order to address a full range of sustainability challenges. Two major shortcomings, however, are hindering these efforts towards a 'post-car' city: first, they lack proactive vision towards cities that are not only sustainable but also accessible without cars, and second, they lack effective strategies to deal with strong, built-in systemic resistance to a change of the status quo. This project will generate knowledge addressing these shortcomings. Central to EX-TRA's approach are transition experiments in city streets, or 'intentional, temporary changes in street use, regulation and/or form, aimed at exploring systemic change towards a 'post-car' city'. By way of urban living labs in Amsterdam, Bologna, Milan, Ghent, Munich and London, we will generate insights into: (1) possible combinations of physical design and regulation that increase the types of usage and inclusivity amongst users of city streets; (2) transport and land use conditions for the purpose of enabling and improving walking and cycling accessibility in city districts; (3) shared mobility platforms and micro-mobility and freight delivery options which complement attractive streets and accessible districts; and (4) strategies of change that can accelerate the transition towards a 'post-car' city.