that's an interesting situation you're describing, and I don't think that I've got an answer for your question. The most puzzling part of your statement to me was the part about the flat rail. My limited understanding of how trains stay on their tracks is summarized thus:
The wheels are tapered (or rounded), such that the outside has a smaller diameter than the inside, and are fixed in pairs to axles. If one wheel tries to get ahead of another wheel (as though the bogey is trying to steer off of the tracks), the forward wheel starts to ride on a smaller radius, and the lagging wheel starts to ride on a larger radius. Since the two wheels turn at the same speed (fixed to axle), the forward (outside of turn) one begins to travel more slowly than the lagging (inside of turn) one, and they return to travelling straight-ahead. The tracks are rounded to meet the wheels appropriately (I don't know the details of the track shape).
I wonder how a train would stay on flat tracks?