Abstract
This paper introduces FedST-GNN, a federated spatio-temporal graph neural network that combines encrypted federated averag- ing with frequency-domain Transformers and ADWIN-triggered meta-learning for privacy-preserving passenger flow forecasting. Evaluation on the Copenhagen-Flow dataset (18.7M events, 312 stops) demonstrates 5% and 7% improvements in MAE and RMSE respectively, over Temporal Fusion Transformer baselines, while maintaining 38ms inference latency on commodity hard- ware. During anomalous events such as a city half-marathon, the adaptive drift detection mechanism reduced peak prediction errors by 41% within a 5MB communication budget per federated round. These results establish that federated graph neural architectures can deliver real-time accuracy for intelligent transportation systems while preserving data privacy.