FrogReaver
The most respectful and polite poster ever
The difference is that with a railroad, I still get to play my character within the confines of the train. I can burn one train car down, repair the next, and so on. I may be stuck on the train, but the choices I make while on the train are mine. My agency is limited since some choices(those to exit or stop the train) are gone, but others are still mine to decide.
If the DM is controlling my character, all agency is gone. My PC isn't being forced down a rail. He's not even on a train at that point. All voluntary movement is gone. Even the forward along the rail.
And as both I and @Umbran mentioned, you can accidentally wander off of the rail and be forced back onto the track in a voluntary railroad.
Okay. I feel like you failed to take in the immediate context of the discussion for what I said. I could have been more clear but I think the context was there either way.