Nowadays, there is no regulation for a high speed passenger train passing a freight train on a mixed traffic line. This article analyses this problem from an aerodynamic point of view, studying the loads and moments generated from both tunnel and open air situations. This analysis is intended to provide knowledge from a theoretical perspective and also from an experimental perspective where results were obtained from tests implemented on the track. As a result of the research, several contributions have been suggested in order to ensure a safe circulation with both types of trains in coexistence.