Railway Signalling power
Usually, signals and other equipment (such as track circuits and level crossing equipment), are powered from a low voltage supply (varies with country and equipment). The reason behind this is that the low voltage allows easy operation from storage batteries, and indeed in some parts of the world, batteries are the primary power source, as mains power may be unavailable at that location. In urban built-up areas, the trend is now to power signal equipment directly from mains power, with batteries only as backup.