Signalnovarnostne naprave zagotavljajo varno in zanesljivo urejanje železniškega prometa. Na odprti progi omogočajo večje hitrosti in tesnejše zaporedje vlakov, na postajah pa zavarujejo vozne poti s pravilno lego kretnic in signalov, dokler poteka vožnja vlaka.

Bistveni del starejših signalnovarnostnih naprav je postavljalo, ki ima v spodnjem delu vzvode, s katerimi kretnik na daljavo (s pomočjo žicovodov) spreminja lego kretnic in likovnih (mehanskih) signalov, v zgornjem delu pa so električna bločna polja za povezavo z nadrejenim bločnim aparatom v prometni pisarni, s katerim prometnik daje ukaze za postavitev vozne poti.

Novejše signalnovarnostne naprave imajo le še postavljalno mizo v promet­nem uradu, od koder prometnik krmili kretnice in signale s pomočjo električnega toka. Kretnice so opremljene z elektromotorji, signali pa so svetlobni, z raznobarvnimi lučmi.

Signalling and safety apparatus

Signalling apparatus and all the safety equipment associated with it allows rail travel to be speedy and safe. It protects trains when they are stationary and in motion. It ensures that points and signals are correctly set for their passage.

The control part of traditional signalling and safety equipment has two essential components. At its base is the lever frame. It houses the levers used to change the positions of the points and signals. Above it are the indicator panels. These hold the electric block repeaters that maintain communication with the main control frame in the stationmaster’s office, from which route orders for trains are despatched.

In this tradition, there is a major difference in practice between Britain and the rest of Europe. In Britain, in routine operation, control of the points and signals is primarily in the hands of the signalmen. Elsewhere, stationmasters at smaller stations, or, at larger ones, employees directly responsible to them, exercise overall control. From their master apparatus, they transmit route orders to the signalmen. The master apparatus and the signalmen’s equipment are linked electrically by small built-in hand-cranked generators.

More recent signalling and safety apparatus is confined to a control panel in the stationmaster’s office. The stationmaster operates all the points and signals electrically by remote control. The points are driven by electric motors. The signals, which can show different aspects, or colours, are electrically lit.