Model train

Model train

Model trains and railroads is a big little world, where there is a lot of technology involved in these modern times. There are many concepts and things to know, here are a few of them:

H0 - 1:87 - The most common scale used. A large railroad usually fills an entire room.
N - 1:160 - A smaller scale where details can be hard to see, but room for a larger railroad on the same space.
There are many other scales, but H0 and N are the most common.

Not relevant anymore. Everything runs DCC or a similar digital protocol, making the tracks act like a combined network cable and power supply. Each locomotive have a decoder with a programmable address, and each locomotive can be individually controlled on the same track.

In the analog world, a railroad could be divided into blocks, where power could be switched off a block to allow one train to wait for another to pass. Today this is not necessary, all trains are individually controlled via onboard decoder, and a large railroad is typically operated from a computer with a user interface instead of a controller with a knob.

2-rail / 3-rail
Some systems (Märklin H0) use a middle rail, where the two tracks are connected to ground and the signal is on the middle rail. This allows some loops which would create a shortcut in a 2-rail system, where the signal is on one of the rails and ground is on the other.

National Model Railroad Association (NMRA) have published the Digital Command Control (DCC) specification, which describes all details about the signal on the tracks.