Li, J., Grübel, J., Nadi, A., Snelder, M., van Arem, B. and Gao, J. (2026) ‘Digital twin federation for urban mobility assessment: Definition, pillars, and a human-in-the-loop functional architecture’, Transportation Research Part A: Policy and Practice, 211, 105086. doi:10.1016/j.tra.2026.105086.

Li, Grübel, Nadi, Snelder, van Arem and Gao shift the urban mobility digital twin from a monolithic model toward a federated socio-technical architecture. The iconic idea is the Digital Twin Federation: an assemblage of linked modules that enables iterative exchange between physical mobility systems and digital representations while preserving human-in-the-loop decision points. Its theoretical contribution is to distinguish urban mobility twins from engineering twins, arguing that mobility planning cannot be reduced to automated replication because it is structured by behaviour, stakeholders, land use, policy conflict and uncertainty. Methodologically, the paper combines literature review, conceptual definition, four architectural pillars, stakeholder co-design sessions and a proof-of-concept framework for Amsterdam low-car transition. Its conceptual operation is federated calibration: heterogeneous models, datasets and evaluative criteria become interoperable without pretending to form a single total model. Its bridge to the wider field connects transport planning, cybernetics, smart mobility, participatory modelling and urban systems governance.