3.2.1. Aerodynamic forces on the trainThe time-varying aerodynamic forces of the cars are illustrated in Figure 12. It shows that the forces on the headcar are larger than those of middle-car and tail-car. Inthe light of previous analysis, it may be caused by theflow separation on the nose of head- car to change theflow structure around the train, due to the combinationbetween crosswind and moving train. The results suggest that there may be a larger operational risk in thehead-car when a train travels with a high speed related tonature wind (Guo, Xu, Xia, Zhang, & Shum, 2007; Zhaiet al., 2015). It is worth mentioning that the time-varyingcurve of rolling moment is similar to that of side force,which means the rolling moment mainly comes from the