Interlocking levers refers to the set of systems and devices for controlling and operating the equipment of a station (points, signals, ground signals, level crossings etc.), controlled from a single command post. Interlocking levers serves to establish control and connection between all of this equipment, thus ensuring the transit or manoeuvring of a consist in complete safety. The Italian ACEI (electric interlocking levers) in particular is the finest example of the development of rail traffic management in the second half of the 20th century, and paved the way for modern computerised central interlocking, in conjunction with the use of electronics, of the ACC and ACC – M types.

The schematic plan of a station is a drawing (once created by hand) which shows a diagram of all the station equipment: tracks, switches (plus related equipment for shunting and control), buildings, signals, track circuits, markers for the origin points of routes, any level crossings (plus related equipment for shunting and control), etc.