Model Rail: Track
A model railroad depends on many things working together, but one of the most important is the track itself. Track consists of several components: the rail, the ties and attachment to the ties that holds the rail in gauge, the roadbed and ballast that supports the ties and absorbs noise and the subroadbed that provides a rigid support structure for the roadbed.
Starting from the bottom, subroadbed is often made from plywood, although other substances can be used, including styrofoam (insulation foam or structural shapes such as Woodland Scenics risers). Subroadbed physically supports the track. In the first Sumida Crossing I used relatively simple sheet plywood with foam above it, rather than more sophisticated methods.
Above the subroadbed, the roadbed is a non-structural buffer between the rigid roadbed and the track. Part of its purpose is to absorb vibration (from the motor of the train, among other things) before it reaches the subroadbed, which would tend to amplify it. Roadbed is often made of cork, either cut with a beveled edge to simulate the natural shape of the ballast under the track, or simply made from sheets. In N-scale, roadbed is typically 1/8" (3mm) thick, although 1/4" (6mm) may be used.
On a real railroad, ballast is what the ties sit on, and it fills both a structural role and allows water to drain, preventing wooden ties from rotting. On a model, ties are laid on the roadbed and ballast (if separate) spread around them. For flex track ballast is typically a loose granular substance that is glued in place, which helps hold the ties down. With sectional track, the ballast may be molded with the ties and rails, or not.
Ties are what the rail itself attaches to, and they hold it in position. Real ties may be wood or concrete (or even metal), but model ties are typically made of plastic, although softwood is normally used for hand-laid track. It’s also possible to hand-lay track by soldering rail to ties made from printed circuit board. Because the position of rail needs to be very precise (measured in thousandths of an inch or fractions of a mm) for reliable operation, ties are a critical element. Ties and ballast are also an important visual element in setting the scene, as different kinds of ties are used on different railroads or types of railroads. Often this is a weak point for sectional track, as much of it replicates the typical mid-twentieth century heavy freight rail and wooden ties, which isn't always appropriate for other kinds of railways. For flex and hand-laid track, ties will typically be glued to the roadbed, often using a flexible glue like silicone glue or a silicone-based caulk, but some people prefer hot-melt glue or liquid nails. Sectional track may be nailed through the roadbed to the subroadbed, although this defeats some of the benefit of having flexible roadbed.
The last element is the rail. With flex and sectional track, the rail comes with the ties and is attached to them by the way the plastic ties are molded around it. For hand-laid track, stapes or track nails are used to attach it to the ties (which is why wood is used for hand-laid track ties), or soldering as mentioned above. The width between rails (the “gauge”) is standardized, but the rail itself can come in several heights, measured in thousandths of an inch. Code 80 (or 0.080 inches or 2.0 mm in height) is a typical size for N-scale. This is oversize, corresponding to a full foot high in Japanese N-scale, about twice the correct height, but works very well and the excess size isn’t really apparent from a normal viewing distance. There are smaller rail sizes available, but these may have problems with some rolling stock. Both Kato and Tomix track uses code 80 rail.
When dealing with track switches (a.k.a., turnouts), these are usually described in terms of the “frog number”. The frog is the place where the two inner rails cross, and on the prototype it is usually a single casting that’s bolted to rails at each end. On model switches these can be made of plastic (insulated) or metal (electrically live). The frog number is simply the length to width ratio (of the frog) and in a normal prototype or model frog there’s a mathematical relationship of this to the frog angle (the angle at which the diverging track diverges at the frog). Peco switches are a little different in how they model frogs (see the Peco Track section).
On model railroads, a #4 switch is generally considered fairly sharp and suited only for yard use (although sometimes used for low-speed crossings, industry sidings, etc), #6 is generally considered a typical mainline switch (meaning that it imposes a speed limit but won’t be problematic for long cars at moderate speeds). Larger numbers can be used to replicate higher-speed crossings or sidings. On the prototype, much larger numbers are typical (a #15 would be a moderate-speed mainline switch, and #20 are fairly common, allowing up to 40 mph, 64 kph, use).