On “real world” railroads, the tracks are divided into the main line, and the “yards.” The difference is fairly self-explanatory, and the rules for moving cars in the yards are different from moving them on the main lines. The tracks in the yards must be kept separate from the tracks of the main line by switches that have to be operated on the orders of the dispatcher.
If you’re interested in model railway layouts, you’ll find that yards are fairly easy to incorporate into your design. One of the biggest problems most model railway enthusiasts have is laying out their main model rail line to fit within the space they have available while allowing for as many fun train maneuvers as possible while still conforming reasonably well to the operating standards of actual real world railways.
Starting with the design of your main line, it helps to realize that there are three basic kinds of main lines: continuous, point-to-point, and out-and-home. Continuous lines have no terminal. Point-to-point lines have a terminal at each end, and out-and-home lines have a terminal at one end, and a loop that reverses at the other end before bringing the train back home. You can take these three and adapt them to curve through and fit into your particular model railroad space.
It’s a good idea to start with a scale drawing of your layout area, trying various sketches to see what might work well. As rules go: it’s pretty simple. You should strive to include the greatest length of line in your space without overcrowding. The National Model Railroad Association guidelines state that your smallest curve should have a 5-foot radius for O scale tracks, 2-foot 6-inch radius for OO scale, and 2-foot radius for HO scale.
The continuous line is the favorite of model railroad enthusiasts for many reasons. It can wind several times around a four-sided room before completing its full length, maximizing the length of track versus floor footprint. This type of layout also lends itself to extensive scenic additions, and gives the conductor free use of lots of fun, wide-swinging curves. It also allows straightaways, curves, and sneak-offs. You can set it up so that a train leaving one station has to curve around three sides of the room before reaching the next station, while going over cross-overs and even through tunnels.
One great feature is to set up your tunnels and cross-overs so as to create a sneak-off, where you think a train is going to go one way, but instead it sneaks off another way. For instance, by having a long straight stretch leading up to a tunnel, you give the viewer the impression that the train will continue going straight after emerging from the tunnel. But by adding concealed curves, you create a sneak-off, which breaks up the monotony of a train merely going around and around in one loop. Every good model train layout should have at least one sneak-off, and preferably more, to keep things as interesting as possible.
Point-to-point lines are not as easy to successfully incorporate into home-based model layouts because of space limitations. To keep things to scale, you need lots of space surrounding each terminal, and sufficient space between the terminals in order to appear remotely realistic. A terminal with its many platforms and switches requires something like 900 scale feet, and it’s not easy to put two of those sufficiently far apart in a home model train layout. However, you can cope with the dearth of space between terminals by inserting in between them features like facing cross-overs so that a train coming from either terminal has to cover a lot of repeat mileage before getting to the other terminal. Sneak-offs can be good helping features in point-to-point layouts as well, as can way stations, elevated tracks, and strategically placed scenery.
Out-and-home lines should also incorporate elevated tracks and way stations to help liven up the layout. Adding additional crossovers will maximize the track mileage a train has to conquer before reaching the terminal loop and returning to the home station. Facing crossings are often necessary with point-to-point and out-and-home lines to give the layout enough running distance to be interesting. This can involve tucking a continuous line into the midst of the setup. You really can’t avoid adding in a continuous line in the middle somewhere unless you have an extraordinary amount of room for a point-to-point or straight-line setup.
Most model railroad enthusiasts start out by designing and building some form of continuous line with an eye toward modifying it later on into a point-to-point or out-and-home layout. This may be done by cutting a terminal into the main line and adding a reversing loop at some point. Or instead of a loop, you could have a switch leading to another terminal, making a version of a point-to-point line. You can get really creative with combinations of continuous lines, switches, and terminals to create an effective point-to-point line without having to have a gargantuan design space to work with.