In this talk we present a sensitivity analysis of a PDE model for traffic forecast on networks. The analysis is made with respect to the parameters and to the network. In order to compare different numerical solutions coming from different inputs, we will use the Wasserstein distance, computed by a suitable numerical method. Traffic uncertainty is evaluated for different initial data, different fundamental diagrams, different vehicle distributions at junctions and different network sizes. Joint work with M. Briani and E. Cristiani.