Trade-Offs Between 2-Rail and 3-Rail Track
Model train rails were first designed with two rail tracks to match the real trains they were designed to resemble.
But it became apparent that electric trains worked better on model train rails that had the electric feed on a center track and both outside rails used for grounding. There are fewer shorts in the current and most model trains have gone to this setup.
3-Rail Track Advantages
During the development of the model train, layouts became more complex and another reason for the third track presented itself in the reverse loop.
If a train goes through a turnout to a loop that reverses the direction of the train, a train rail, two-rail electrical system would have a short-circuit, but the three-rail doesn’t because the outer tracks are identical no matter which way the train is going.
Another great advantage to the model train rails, is the three-rail system that it makes it possible to operate other functions. A railway signal can be wired to a track section that has one rail insulated.
When the train crosses that section, the circuit is completed making the railroad-crossing signal operate. This same scheme can be used for such operations as turnouts.
Railroad Car Compatibility
It is possible to use railroad cars of the same scale on either a two-rail or a three-rail system with some modifications. Those that are designed for a three-rail must have the wheels insulated from one side to the other if they are used on a two-rail track.
The disadvantage of using a two-rail railroad car on a three-rail system is that the wired controls for specialty features won’t work.
Model railroad hobbyists often convert cars from one system to the other.
The simplest way to change a car is by replacing the wheel assemblies. Someone not associated with model railroads might wonder why anyone would bother with remodeling rather than just buying new railroad cars.
Of course, the person who has favorite train cars wants to be able to use them even if the track size changes.
Center Rail Concealment
Because train modelers want to make everything look as much like the full size trains as possible, the third rail has always been detrimental to the realism.
Lionel made a design change to hide the center rail by making it thinner and painting it black to be less obvious. Since the 1950’s, other manufacturers have followed suit, most notably on the O scale.
Another innovative way to conceal the center rail was devised by Märklin. The model train rails were concealed within the cross ties. While not completely invisible, it is not obvious to the untrained eye.
This design is called a “stud” system because that is what can be seen, and it is often used on garden railway systems due to its ability to handle the outdoor elements better than the standard three-rail.
All manufacturers do not wire the model train rails the same.
The more common wiring has the two outer rails tied together, but some producers insulate all three track rails independently of each other. This allows a non-computerized system to run two trains at the same time on one track.
Model Train enthusiasts will forever be at odds about the different model train rails systems, but the three-rail is obviously the more versatile of the two. If any designer can make the center train rail truly invisible, all model trains would probably follow that technology.