All moveable bridges use invisible track.
Why?
1. If you try to put real track on the moveable part, it won't move when the structure opens and closes (or I've never been able to get it to move). Looks really dumb hanging in the air with no bridge around it, lol.
2. If you could get it to move there is no certainty it would "connect" to the track on the non-moveable parts (derailments here we come).
What you see on moveable bridges is fake track (parts that look like ties and rails but aren't). A train actually crosses the span on invisible track. This means if you go too fast the bridge can still be partially open when the engine gets to the moveable part or if you go too slow, the bridge will start to open back up before the caboose gets off the moveable part. They will be magically floating in the air but won't derail.
Ben