Mobility data justice begins from a simple displacement: transport should not be judged primarily by movement, but by access. A city is not just because it contains roads, vehicles, apps, dashboards or modal options. It becomes just when differentiated persons can reach work, care, education, health, food, shade, public life and social connection without excessive cost, risk, waiting, exclusion or bodily exposure. CitationalCommitment names the ethical obligation to account for what is counted, who is cited by data, who is omitted, and how mobility evidence becomes public responsibility. The ITF’s Sustainable Accessibility for All provides the normative centre. Accessibility shifts the question away from kilometres travelled and toward opportunities reached. This matters because mobility can increase while justice decreases. A city may become faster for some and more fragmented for others. It may optimise flows while deepening transport poverty. Access requires person-based and territory-sensitive metrics: age, income, gender, disability, household structure, settlement pattern, service availability, temporal burden and digital connectivity all matter.

Behrendt and Sheller’s concept of mobility data justice deepens this by showing that movement now generates data almost continuously. Ticketing systems, navigation apps, shared mobility platforms, sensors, vehicles, road infrastructures and environmental monitoring systems all produce traces. But datafication is uneven. Some movements are over-visible and surveilled. Others are absent, informal, too complex or institutionally ignored. MetadataSkin becomes important here because the outer informational layer attached to mobility users can determine how they are represented and governed. The skin is not superficial. It mediates access, risk and recognition. Recent work on mobility equity metrics attempts to formalise fairness within intelligent transportation systems. Bang and colleagues propose a metric combining service accessibility and transport cost, using distributional tools to evaluate fairness. Such work is valuable because it pushes equity into system design rather than treating it as a rhetorical appendix. Yet CitationalCommitment also asks what every metric leaves outside. A Gini coefficient may show distributional inequality, but it may not capture fear, heat, humiliation, disability friction, care work or attachment to place. Metrics must be treated as instruments, not substitutes for politics. AI-powered transportation digital twins add further complexity. Fu and colleagues describe cyber-physical transport twins with sensing, prediction, decision-making and feedback. Their distinction between a twin’s eyes and brain is useful: perception alone is insufficient without interpretation and response. But the political question remains: whose vulnerability does the twin detect? Vulnerable road users may be technically recognised while other vulnerable populations remain invisible. LegibleArchive becomes relevant because mobility data must not be only real-time flow. It must also preserve evidence, provenance, historical inequity and accountability over time. Climate makes mobility justice more material. Cabrera, Ziegler and Schläpfer’s work on targeted cooling of cycling networks shows that heat exposure concentrates unevenly across routes. A small portion of a network may generate disproportionate thermal burden. CDRI’s guidance on heat management in public transport similarly treats heat as an operational and equity issue. Shade, waiting, station design, vehicle comfort, hydration, surface temperature and elderly bodies become transport variables. Thermal stress reveals that access is never abstract. A route may exist and still be unusable under climatic pressure.

Digital Twins as Catalysts for Urban Sustainability

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