Many of our model railroads feature hidden trackage. While some will say it is important to keep this trackage to a minimum, short stretches of hidden track can make a railroad seem larger and separate scenes.
If you've built your platform using an open grid or L-Girder style of benchwork, there is often not much between your trains and the floor. Scenery fills the void over most of the railroad - but what about those hidden tracks underneath?
Sadly, most of us have learned the hard way that our trains will find any path they can to fall to the floor. Fortunately, the solution to these potentially expensive disasters are often very inexpensive and easy to install.
Protecting the Sides
The most vulnerable areas of hidden track are along the sides. One option is to enclose your tunnels with a tunnel liner which not only will keep the trains from heading to the floor, it will also provide a more realistic look.
But for really long hidden stretches, a full liner the entire length of the tunnel may provide more problems then solutions. If a train does derail in there, how will you get to it? After a few inches of track - past the point you can see through the entrance - you can simply install small shields along the side of the plywood base.
You can use a variety of materials. Plexiglass allows a view of the trucks and the problem. Thin strips of hardboard, luan or even a stiff cardboard will also offer plenty of protection at low cost and with good flexibility for curves.
Cut the strips just high enough to reach the carbodies of your equipment. This will prevent them from going over the edge, but also still give you room to get fingers over the top of the barrier to retrieve or rerail your cars.
Of course these same techniques will work on any stretch of track - hidden or not. Fasten protection strips along your roadbed where scenery has yet to be installed or on narrow swing bridges or other access sections.