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 digital twin from a monolithic technical replica to a federated socio-technical assessment system. The iconic idea is the Digital Twin Federation: an architecture that links physical and digital mobility systems, monitoring and planning, outcome evaluation, immersive experience and human-in-the-loop control. Its theoretical contribution is to redefine mobility twins against the limits of automated engineering models, acknowledging that urban mobility is shaped by stakeholder judgement, behavioural change and iterative public decision-making. Methodologically, the work combines conceptual definition, stakeholder co-design sessions and proof-of-concept architecture, producing a modular framework rather than a closed simulation. Its conceptual operation is federation: distributed models become interoperable without being collapsed into a single totalising system. The bridge to the wider field lies in its connection between transport modelling, participatory planning, cyber-physical systems and socio-technical governance, opening digital-twin research to deliberation, uncertainty and human control.