The Barcelona Circular City model, presented by vCity and documented in recent simulations and reports, exemplifies how Digital Twins function as vital instruments for designing and monitoring urban transitions toward sustainability; by virtually replicating city systems in real time, these models enable urban planners to simulate, evaluate and optimise infrastructure, transport, energy and waste management under a holistic lens, integrating social, economic and ecological indicators into a single decision-making environment, especially when guided by frameworks like the Circular City Index, an open-data tool that benchmarks municipal progress across Spain, fostering comparability, policy learning and accountability through a reproducible methodology anchored in transparency and inclusivity, as demonstrated in applications ranging from mobility flows in Viladecans to charging station coverage in Barcelona, where complex spatial datasets are transformed into actionable insights; for instance, in the case of the 15-minute city simulation for Barcelona, the model exposed areas of uneven accessibility to basic services, prompting tailored interventions such as redistributed libraries and expanded metro access, thus evidencing how the digital twin does not merely reflect urban reality but proposes corrections to its inertia, which is further illustrated in the comprehensive report “Circular Barcelona: A New Urban Model” (October 2025), where digital infrastructure and circular economy converge in a civic-technological alliance for resilient futures, co-funded by European recovery programmes and hosted at the Barcelona Supercomputing Center, this initiative operates at the crossroads of research, policy and digital transformation, empowering local governments to shift from reactive to anticipatory planning while anchoring decisions in measurable sustainability metrics. vCity (2025) Report. Circular Barcelona: A New Urban Model. Barcelona Supercomputing Center, https://vcity.tech
