Signalling block system
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Signalling block systems enable the safe and efficient operation of railways, so as to avoid collisions between trains. Block systems are used to control trains between stations and yards, and not normally within them. Any block system is defined by its associated physical equipment and by the application of a relevant set of rules. Some systems involve the use of signals, while others do not. Some systems are specifically designed for single track railways, where a danger exists of both head-on and rear-end collision, as opposed to double track, where the main danger is rear-end collision.
A block system is referred to as the method of working in the UK, method of operation in the U.S, while in Australia they come under the heading of safeworking. The objective of this article is to describe the various methods of block signalling used around the world.
- 1 Block signalling methods
- 1.1 Strict timetable operation
- 1.2 Timetable and Train Order
- 1.3 One Train Working
- 1.4 Electric Train Staff (ETS)
- 1.5 Ordinary Train Staff and Ticket (OTST) or (OTS&T)
- 1.6 Ordinary Train Staff sections
- 1.7 Telegraph Block
- 1.8 Tokenless Block
- 1.9 Absolute Block
- 2 Comparison of block systems
- 3 References
Block signalling methods
Strict timetable operation
Trains operate according to a strict timetable, that is cannot leave a station until an appointed time and until any other trains they were to meet at that station have arrived. Rarely used as a block system, as if one train is delayed, all trains it is scheduled to meet are delayed. This can quickly lead to all trains on the railway being affected.
This method is not authorised for use in the UK.
Timetable and Train Order
Popular on single track lines in North America up until the 1980s, Train Order operation was less a block system and more of a system of determining which trains would have the right of way when train movements would come into conflict. Trains would make use of a predetermined operating plan known as the timetable which made use of fixed passing locations often referred to as stations. Amendments to the operating plan would come from a train dispatcher in the form of train orders, transmitted to the trains via intermediaries known as agents or operators at train order stations.
This method is not currently authorised for use in the UK. A similar system, known as Telegraph and Crossing Order, was used in the 19th century, but after three serious head-on collisions in the 1870s (Menheniot, Cornwall Railway, 1873; Thorpe, Great Eastern Railway, 1874; Radstock, Somerset & Dorset Railway, 1876) its use was condemned.
In North American train order system was often implemented on top of other block systems when those block systems needed to be superseded. For example where manual or automatic block was implemented, train orders would be used to authorize movements into occupied blocks, against the current of traffic or where no current of traffic was established.
One Train Working
One Train Working (with train staff)
If a single track branch line is a dead end with a simple shuttle train service, then a single token is sufficient. The driver of any train entering the branch line (or occupying any part of it) must be in possession of the token, and no collision with another train is possible. For convenience in passing it from hand to hand, the token was often in the form of a staff, typically 800 mm long and 40 mm diameter, and is referred to as a train staff. Such a staff may be a wooden staff with a brass plate stating the section of line on which it is valid, or it may be in the form of a key.
In UK terminology, this method of working was originally referred to as One Engine in Steam (OES).
One Train Working (without train staff)
A modern variation of the One Train Working system operates without any train staff. On these lines the clearance of the controlled branch entry signal is the driver's sole authority to enter the branch, and once the train has passed that signal, the interlocking will hold it at 'danger' (and the signal cannot be cleared a subsequent time) until the branch service train, on its return journey has sequentially operated two track circuits at the start of the branch. Continuous train detection on the branch is not required. Safety is ensured by the interlocking circuitry, and if a track-circuit failure occurs then special emergency working by pilotman must be introduced.
Electric Train Staff (ETS)
These came in two sizes, large and miniature.
Ordinary Train Staff and Ticket (OTST) or (OTS&T)
Ordinary Train Staff sections
Some low traffic lines dispensed with Tickets and became Ordinary Train Staff sections (OTS).
Used on multiple track sections whereby the passage of trains from one point to the next was controlled by instruments connected by telegraph wires. Used extensively in Australia.
This a system for use on single track railways, which requires neither the use of tokens nor provision of continuous train detection through the section. The signalling is designed such that the controlling signals will only allow one train to enter the line. The signalman at the far end of the section must visually check that the whole train has left the section and not become divided. Examples abound on railway systems throughout the world. The absence of a token does remove the one visible reassurance that the driver has and head on collisions have occurred where the driver of an unauthorised train has proceeded under the mistaken idea that he has authority to occupy the line.
Comparison of block systems
|Method of working||For use on||Movement authority by||Line proved clear by|
|Timetable operation||Single track||Adherence to timetable||Adherence to timetable|
|Timetable and train order operation||Single track||Adherence to timetable or possession of written train order||Adherence to timetable|
|Track warrant control||Primarily single track||Possession of track warrant||Dispatcher's receipt of verbal advice via radio that previous train has vacated the section|
|Direct traffic control||Primarily single track||Verbal authority via radio||Dispatcher's receipt of verbal advice via radio that previous train has vacated the section|
|Time Interval Working||Single or multiple track||Handsignal or clearance of section signal||Period of time elapsed since passage of previous train|
|One Train Working (with train staff)||Single track branch lines||Possession of train staff (and clearance of section signal, where provided)||Possession of train staff|
|One Train Working (without train staff)||Single track branch lines||Clearance of section signal||Sequential operation of train detection at entrance to section|
|Train Staff & Ticket||Single track||Possession of train staff or ticket (and clearance of section signal, where provided)||Overlaid block system or time interval working|
|Divisible Train Staff||Single track||Possession of train staff or portion thereof (and clearance of section signal, where provided)||Overlaid block system|
|Electric Token||Single track||Possession of token (and clearance of section signal, where provided)||Possession of token, cooperation between signalmen and signalman visually observing that previous train has vacated the section|
|No-signalman Token||Single track branch lines||Possession of token (and clearance of section signal, where provided)||Possession of token|
|No-signalman Token with Remote Crossing Loops||Single track||Possession of token||Possession of token|
|Radio Electronic Token Block||Primarily single track||Electronic token and verbal permission via radio||Possession of electronic token and signalman's receipt of verbal advice via radio that previous train has vacated the section|
|Tokenless Block||Single track||Clearance of section signal||Cooperation between signalmen and signalman visually observing that previous train has vacated the section|
|Absolute Block / Manual block||Primarily multiple track||Clearance of section signal||Cooperation between signalmen and signalman visually observing that previous train has vacated the section|
|Track Circuit Block / Centralized traffic control||Single or multiple track||Lineside signals||Continuous train detection|
|Cab signalling (various systems)||Single or multiple track||Cab signals||Continuous train detection|
|ERTMS Level 1||Single or multiple track||Lineside signals or cab signals||Continuous train detection|
|ERTMS Level 2||Single or multiple track||Lineside signals or cab signals||Continuous train detection|
|ERTMS Level 3||Single or multiple track||Cab signals||Train continuously reports its position via GSM-R radio|
|This article needs additional citations for verification. (July 2006)|