Bridges are a way to change up your model train layout and express your creativity. Bridges can be constructed of anything sturdy enough to support your model trains. They also allow you to add other model features like rivers, lakes, ponds or industrial areas. Once you've mastered the bridge, there's nothing you can't build.
Determine the width and length of the bridge you want to build. Build a base for the train tracks using wood strong enough to support your landscape and trains. The larger-scale your trains, the larger the wood you need to use. It's generally recommended that you use 2 by 4's. Build a basic box form and cover it with plywood.
Create a pattern for the arches on your viaduct by deciding how many you want and how large they should be. Decide if you want a train to be able to pass between the viaduct arches. Space them evenly throughout the structure.
Secure two sections of foam core, or MDF, and trace your viaduct pattern onto the top sheet. Cut them out at the same time to insure they match up exactly and glue them to your track bed. Allow the glue to dry thoroughly.
Flip your track bed upside-down to have easy access to the underside of the model train bridge.
Strengthen the model train bridge with supports in between the arches. Cut sections of foam core to fit snugly, and make sure they're level with the bottom of the viaduct. Glue them into place let them dry thoroughly.
Decorate the outside of your viaduct bridge by covering it with paper printed to replicate bricks or another construction material of your choice.
Secure your viaduct bridge into your layout and add the rail bed and train tracks.
Use the lid to a paint bucket or a plastic food container to draw your arches evenly. The size of the lid you use should be adjusted to suit your design. A small-scale design should use a small lid or even a drinking glass.