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Historically, there were as many different French railway signaling systems as there were private companies.
An initial alignment was undertaken in 1930 following the work of the Commission Verlant (named Director of Exploitation of PLM).
It was not until the nationalization of all networks and reconstruction undertaken after 1945 that real harmonization is born.
As the trains generally run on the left track, signals are located normally on the same side.
Their function is to inform and provide guidance to drivers.
Each lane is divided into sections, called "block".
It can't be more than one train per block, and its access is protected by a signal.
The SNCF' mechanical signals sysem is charateristic of the 60' / 70'. It has been maintened until these days on some single track lane.
With this sort of equipment, each block is manually managed by an agent : it is the manual block system.
It cannot be more than one block between each station (unless the rare case of an intermediate signal box), and therefore no more than one train.
Trains crossing on a single track lane runs into a station and is subject to particular signals.
Vocabulary:
Switch : forking between two tracks ; according to the direction of travel, train runs through switch (the track joins another) or through point (track splits into two).
Target : this term refers to the swivel panel of a mechanical signal.
Closed/open : a signal is closed when it presents its most restrictive aspect ; It is open when it présents no restriction
Protection signals : those signals protect a particular point (switches or any others facilities) - photo above -
Blocks signals : they protect the access to a block ( i.e. a lane between two stations)
Announcer signals : they inform the engineer about a next restriction (stop, slowing down,...) - photo on previous page -
Deferred stop signal : characteristic of crossing into station and manual block (see below)
Board : fixed indicators (in opposition with the signals) informative ou prescriptive - ex. : speed board, level crossing announcement,...
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