Why flange of train wheel is inside the track?

Why not have them on both? Surely then they would be safer? I don’t know to be honest and would have to ask people/research and I am so tired, and it is late. Maybe someone else can shed more light on the situation :)

As a train goes around a turn, if it tips, a flange on the outside would allow it to slip off of the track. A flange on the inside stays against the rail.

For a real answer read Mylo’s responses here:
http://www.engineersedge.com/wwwboard/posts/4355.html