Fundamentally, static friction is the force that's going to be preventing the train from starting to move. If you had a semi-truck in neutral on a flat surface,

Fundamentally, static friction is the force that's going to be preventing the train from starting to move. If you had a semi-truck in neutral on a flat surface, I don't think you would be able to push it. The wheels aren't slipping on the ground, but rather it must be in the bearings. The problem is F=ma. In this case m is large.