Interlockings rely on a combination of mechanical, electrical, and electronic equipment to safely control train movements. Each component has a specific purpose, and all components must work together to prevent conflicting routes.
Track switches, also called points, are movable sections of rail that allow trains to move from one track to another. These switches are normally operated by switch machines, which move, lock, and detect the position of the switch.
Signals provide visual indications to train crews. They tell the crew whether to stop, proceed, or move at a restricted speed based on the route that has been established and the condition of the track ahead.
Interlocking logic is the control logic that coordinates switches, signals, and track occupancy. Its job is to make sure only safe routes can be established and that conflicting routes are blocked.
Track circuits detect the presence of trains within a section of track. This information is sent back to the interlocking logic so the system knows whether a track section is occupied or clear.
Modern interlockings may also include computers, microprocessors, communication networks, diagnostic systems, power supplies, relays, cables, and control interfaces. These systems allow dispatchers and maintainers to monitor and control the interlocking safely and efficiently.