In this article, a numerical model for the pneumatic braking system of traditional freight trains is developed and tested. The validation of the results is performed through the comparison of the numerical results with analogous experimental data. The model has proved to be reliable and computationally efficient either for simple braking and releasing manoeuvres or for complex/transient manoeuvres. This model has been included in the software TrainDy, and thanks to its key features it has gained the Union Internationale Chemin de fer certification.