Moveable sections can take many forms, all are essentially lift-outs attached to the layout with hinges at one end. Swing bridges move side to side. Lift or drop bridges move up and down like a drawbridge. While all are similar in function, the decision to go vertical has its own peculiar challenges.
Advantages of a Lift Bridge
- Compact footprint: Even a long bridge has a very small footprint when folded up or down. Just remember it will be as tall as it is long; your vertical clearance may determine the length of the bridge.
- Simple operation: Lift bridges are easy to use and align quickly. They are well suited for high-traffic, high-use installations.
- Electrical Connections: With one fixed end, a flexible but solid electrical connection is easy to install.
Design Tips for a Lift Bridge
- Hinges: Hinges don't have to be big to handle the weight of a lift bridge. If the bridge will be raised when open, keep the hinge point as high as or higher than the top of the rails. This will lift the bridge slightly above the fixed tracks when raised. If the bridge drops to open, hinge placement will have a more prominent effect on the open end of the bridge.
- Level: A lift bridge doesn't have to be level, but it is generally easier to build one if it is. Even if the track is on a grade, creating a level base and supports for the bridge greatly simplifies things and improves functionality.
- Alignment: Keeping the end of the bridge opposite the hinges aligned in important. Blocks of wood on either side of the bridge help guide and lock it into place.
- Tapered ends: With any moveable bridge, there is a little geometry involved in matching up the open end. The bridge will swing in an arc from the hinges. Therefore everything must be built around this radius in order to clear the fixed end of the railroad. Support structures must be set back from the end accordingly.
- Kill Switch: Getting power to the bridge is as simple as a flexible wire connection. But what about an open bridge? Trains on the floor can be prevented by installing a kill switch into the bridge mechanism. This can shut off power to the bridge and the approaches when open.
- Protection: Additional fall protection can be provided by installing shields of plexiglass or other materials to the sides of the bridge. Faux bridge girders are a common option. These only need to be high enough to prevent a fall in case of derailment.