Editing Rail transport modelling (section)

== Control ==
[[File:Coinop trains.jpg|right|thumb|Coin-operated model train layout in Germany]]
The first clockwork (spring-drive) and live steam locomotives ran until out of power, with no way for the operator to stop and restart the locomotive or vary its speed. The advent of electric trains, which appeared commercially in the 1890s, allowed control of the speed by varying the current or voltage. As trains began to be powered by [[transformer]]s and [[rectifier]]s more sophisticated throttles appeared, and soon trains powered by AC contained mechanisms to change direction or go into neutral gear when the operator cycled the power. Trains powered by DC can change direction by reversing polarity.

Electricity permits control by dividing the layout into isolated blocks, where trains can be slowed or stopped by lowering or cutting power to a block. Dividing a layout into blocks permits operators to run more than one train with less risk of a fast train catching and hitting a slow train. Blocks can also trigger signals or other accessories, adding realism or whimsy. Three-rail systems often insulate one of the common rails on a section of track, and use a passing train to complete the circuit and activate an accessory.

Many layout builders are choosing digital operation of their layouts rather than the more traditional DC design. Of the several competing systems, the command system offered by the majority of manufacturers in 2020 was a variant of [[Digital Command Control]] (DCC). The advantages of DCC are that track voltage is constant (usually in the range of 20 volts AC) and the command throttle sends a signal to small circuit cards, or decoders, hidden inside the piece of equipment which control several functions of an individual locomotive, including speed, direction of travel, lights, smoke and various sound effects. This allows more realistic operation in that the modeller can operate independently several locomotives on the same stretch of track. Several manufacturers also offer software that can provide [[computer]]-control of DCC layouts.

In large scales, particularly for [[garden railway]]s, radio control and DCC in the garden have become popular.