|An Introduction to
Single-Line Block Working
This is an Introduction page about the various methods of Single-Line Block Working used on the railways of the UK West Country. Details of the actual systems used on individual sections are listed in a separate RailWest Register of Single-Line Sections.
It is not intended to provide a detailed description of the actual method of operation of the different forms of single-line block working, as that subject will be covered elsewhere. Some information on single-line control instruments can be found in The Signal Box website and it is hoped to include more details in RailWest in due course. The information on this page will provide a background to the details set out in other RailWest pages.
Until about 1890 most (but by no means all) single-line block sections in the West Country were controlled by the "Train Staff and Ticket" (TS&T) method. After the invention of the Electric Train Tablet (ETT) system by Edward Tyer in 1878 the London & South Western Railway (L&SWR) eventually adopted ETT as their standard for new works, as well as fitting it retrospectively in due course to all their existing sections. Under their influence ETT was applied gradually also to the Somerset & Dorset Joint Railway (S&DJR) from 1885 onwards, although one S&DJR section did remain as TS&T until British Railways (BR) days.
By contrast the Great Western Railway (GWR) adopted the Electric Train Staff (ETS) system patented by Webb and Thompson in 1889 and they deployed this extensively throughout their system. [This equipment is sometimes called the 'large' ETS to distinguish it from a smaller 'miniature' ETS system developed later by the Railway Signal Company.]
About 1908 the GWR adopted the Tyer's No 7 pattern of ETT as their standard instrument instead of ETS, but in the event only a few sections were fitted with this equipment before there was a further change of policy.
In 1912 GWR engineers Blackall and Jacobs invented the Electric Key Token (EKT) system and thereafter the GWR used EKT for new work and the replacement of old equipment. The GWR also licensed their EKT system to Tyer, who then manufactured EKT equipment for other railways (usually with variations in design).
In later years the Southern Railway (SR), and then BR Southern Region (BR(SR)), used Tyer's EKT as a replacement on several ETT sections, although their style of token varied from the pattern used by the GWR and BR Western Region (BR(WR)). However in the West Country most (but not all) examples of EKT equipment on former SR lines were fitted in fact after 1948 by BR(WR) using the ex-GWR pattern.
Some other varieties of single-line control also existed in the West Country, such as a few One Engine in Steam (OES) sections, some No Signalman Key Token (NSKT) working, and a solitary example of the Railway Signal Company's Miniature ETS. There were also a few examples of 'long section' working, where an intermediate signal-box could be 'switched out' and the two 'short' sections on either side of it worked as a single 'long' section, and sometimes different control systems were used for the 'long' and 'short' sections.
Wherever there were two or more adjacent sections of single-line worked by some form of staff, tablet or token then it was vital to ensure that the driver of a train entering a section was not given the wrong staff/tablet/token by mistake - with potentially disastrous results. Apart from the driver being required to satisfy himself that he had the correct item before entering the section, a further safeguard was provided by what is known usually as the 'configuration' of the staff/tablet/token. [The term 'configuration' probably only applies really to the various 'electric' systems - ie ETT, ETS and EKT - but a similar principle applied to the 'manual' OES and TS&T systems.] Configuration information for individual sections (where known) is included in the RailWest Register.
For the 'manual' OES and TS&T systems the 'configuration' was achieved usually by one or both of two methods - the colour of the train staff and the shape of its cross-section. Colour was used for visual identification in daylight, whilst the cross-section shape enabled the staff to be identified by touch at night. Typical examples of staff configuration might be "round, red" or "square, blue" etc. In all cases the staff would bear the name of the section to which it applied - usually the names of the signal-boxes at each end of the section. In the case of TS&T the tickets themselves might also be of the same colour and/or shape as the relevant staff, although on some sections different colours were used for the tickets for 'Up' and 'Down' directions.
|Example of One-Engine-in-Steam Staff Configuration|
|A typical BR(Western Region) "Round, Red" train staff|
|NOTE: there is an Annetts Key attached at the left-hand end to unlock a ground-frame|
|Examples of Train Staff Tickets|
For the 'electric' ETT, ETS and EKT systems the 'configuration' was achieved by some aspect of the mechanical form of the staff/tablet/token, usually the position and/or shape of a notch or ring. The purpose of this aspect of the configuration was to prevent the staff/tablet/token being replaced into the wrong instrument after use. Sometimes there was also a variation in shape and/or the use of different colours and this provided visual identification of the correct item. In all cases again the staff/tablet/token would bear the name of the section to which it applied - usually the names of the signal-boxes at each end of the section. Sometimes also the individual staffs/tokens/tablets for any given section were numbered (from 1 upwards), but this numbering played no part in the actual operation of the system.
Generally the configurations for the different types of ETS, ETT and EKT equipments were standardised and identified by letter - 'A', 'B', 'C' and 'D' (configuration 'D' appears to have been rare with ETS and ETT). In some cases this letter was engraved on the item itself and/or the instrument in which it was kept, although this appears to have been a practice mostly confined to ETS (both 'large' and 'miniature' versions). For ETS and EKT there was also a colour code associated with each configuration, which was usually as follows:-
|A = Red||B = Blue||C = Green||D = Yellow|
although some key tokens installed by the SR or BR(SR) used a different sequence. A further identification of configuration was provided on SR/BR(SR) key tokens by the shape of the handle and/or a hole in the centre of the handle, but GWR key tokens merely had a plain rectangular handle painted in the appropriate colour.
|Examples of Electric Train Staff Configurations|
|Configurations 'C', 'B', 'A', 'D' from top to bottom|
|The configuration is set by the position of the single ring on the left relative to the four rings in the centre|
Most Tyer's tablets were circular, although their diameter varied depending upon the particular model of instrument. Although Tyer did manufacture square tablets for use with 'long section' working, no examples are known to have existed in the West Country. However there was one 'long section' on the S&DJR which used 'square tablet' instruments supplied by McKenzie & Holland.
|Examples of Electric Train Tablet Configurations|
|Configuration 'A'||Configuration 'B'||Configuration 'C'|
|Round centre hole
Round notch in edge
|Square centre hole
|Triangular centre hole
Combined rectangular + long round notch
NOTE: In the 'C' configuration tablet the left-hand rectangular notch is NOT part of the normal configuration. The small circular hole seen at the top of each picture was also not part of any configuration, but provided probably to enable the signalman to remove the tablet from the drawer of the instrument.
© Chris Osment 2014
ETS photographs © David Hayball