Radio Electronic Token Block
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Radio Electronic Token Block is a system of
railway signalling Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormou ...
used in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. It is a development of the physical token system for controlling traffic on single lines. The system is slightly similar to North American
Direct Traffic Control Direct traffic control (DTC) is a system for authorizing track occupancy used on some railroads instead of or in addition to signals. It is known as "direct" traffic control because the train dispatcher gives track authority directly to the train ...
, which unlike RETB does not have a cab display unit.


Operation

On arrival at a "token exchange point", the driver reports their position to the
signaller A signaller, signalman, colloquially referred to as a radioman or signaleer in the armed forces is a specialist soldier, sailor or airman responsible for military communications. Signallers, a.k.a. Combat Signallers or signalmen or women, are ...
by radio and requests the "token" for the next section of line ahead. If the signaller is in a position to do so, they will issue the electronic token applicable to the section ahead. Simultaneously, the driver must operate a button on an apparatus in the cab to receive the token. The token is then transmitted to the train by radio. The
Solid State Interlocking Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...
controlling the system prevents the issue of any token permitting conflicting movements. In the same way as with the traditional system, when a physical token with the name of the section engraved on it would be carried in the cab, the electronic token is received and displayed by name on the train equipment. This token is the authority to occupy the single line, and it cannot be removed from the train until the driver themself releases it. After receiving the token, the driver is then given verbal permission to pass the "Stop Board" and enter that section; the stop board is used instead of signals and therefore needs no electrical supply. The fixed distance board on the approach has a single permanent AWS inductor which gives a warning in the cab regardless of the signal box instruction and has to be cancelled when passed. Points at the entrance to a
crossing loop A passing loop (UK usage) or passing siding (North America) (also called a crossing loop, crossing place, refuge loop or, colloquially, a hole) is a place on a single line railway or tramway, often located at or near a station, where trains or ...
are spring-loaded for the correct track for facing movements, and are pushed across by the wheels for trailing movements; they too require no power or
interlocking In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junction (rail), junctions or crossings. The signalling appliances and Track (rail transpor ...
, other than for points heating purposes. In the facing direction, a 'points indicator' is provided to indicate to the driver that the points are correctly set. The points indicator is in the form of a yellow light, lit only while the points are electrically detected in the required position. The whole line can be operated by just one or two signallers and needs very little infrastructure other than the track itself, making it a very cost-effective method. The simplicity of the lineside infrastructure in RETB areas was reduced by the installation of the
Train Protection & Warning System The Train Protection & Warning System (TPWS) is a train protection system used throughout the British passenger main-line railway network, and in Victoria, Australia. The British Rail Safety and Standards Board's definition is: The purpose of TPW ...
. A train stop loop is provided at each stop board, and is normally activated (so that any train attempting to pass it will be immediately brought to a halt). When the signaller issues a token for a train to enter a section, the TPWS loop at the appropriate board is deactivated, so allowing the train to proceed. Indication of the state of the TPWS is provided by a blue light mounted below the stop board. This shows a steady blue light when the TPWS is activated, and a flashing blue light when it is deactivated.


History

The genesis of the system was on the
Far North Line The Far North Line is a rural railway line entirely within the Highland area of Scotland, extending from Inverness to Thurso and Wick. As the name suggests, it is the northernmost railway in the United Kingdom. The line is entirely single-trac ...
, a long, remote single-track line between
Inverness Inverness (; from the gd, Inbhir Nis , meaning "Mouth of the River Ness"; sco, Innerness) is a city in the Scottish Highlands. It is the administrative centre for The Highland Council and is regarded as the capital of the Highlands. Histori ...
,
Wick Wick most often refers to: * Capillary action ("wicking") ** Candle wick, the cord used in a candle or oil lamp ** Solder wick, a copper-braided wire used to desolder electronic contacts Wick or WICK may also refer to: Places and placenames ...
and
Thurso Thurso (pronounced ; sco, Thursa, gd, Inbhir Theòrsa ) is a town and former burgh on the north coast of the Highland council area of Scotland. Situated in the historical County of Caithness, it is the northernmost town on the island of Great ...
in
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
. This line was controlled by traditional electric token instruments at each station, but in January 1978 the signal
telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
pole route A utility pole is a column or post typically made out of wood used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It c ...
was brought down by bad weather over more than forty miles of track. The simplest, cheapest and quickest way of restoring the links between the instruments was found to be by radio: each machine was fitted with an external controller containing a unique microprocessor code so that the effect of a dedicated link to the machine at the other end of its section was maintained. The manual issue of the tokens continued as before. With the feasibility of using radio to effect the interlocking of single line token instruments demonstrated, and the additional benefit of voice communication between the signaller and the drivers noted, it was but a short step of invention to moving the instruments from staffed
signal box In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
es to the cabs of trains. The line selected for the trial was another remote and lightly used Scottish line: the old
Highland Railway The Highland Railway (HR) was one of the smaller United Kingdom, British railways before the Railways Act 1921, operating north of Perth railway station, Scotland, Perth railway station in Scotland and serving the farthest north of Britain. Base ...
route from
Dingwall Dingwall ( sco, Dingwal, gd, Inbhir Pheofharain ) is a town and a royal burgh in the Highland council area of Scotland. It has a population of 5,491. It was an east-coast harbour that now lies inland. Dingwall Castle was once the biggest cast ...
westwards to
Kyle of Lochalsh Kyle of Lochalsh (from the Scottish Gaelic, Gaelic ''Caol Loch Aillse'', "strait of the foaming loch") is a village in the historic county of Ross-shire on the northwest coast of Scotland, located around west-southwest of Inverness. It is loca ...
. The contract was placed with Westinghouse of Chippenham, Wiltshire, and the system was brought into use on 28 October 1984, with the control equipment situated at Dingwall. Over the next four years, control was transferred to Inverness and the Wick and Thurso line was included in the scheme. A new control centre was brought into use at
Banavie Banavie (; gd, Banbhaidh) is a small settlement near Fort William in the Highland Council Area of Scotland. One of the closest villages to Ben Nevis, it is about northeast of Fort William town centre, next to Caol and Corpach. It has been sug ...
for the
West Highland Line The West Highland Line ( gd, Rathad Iarainn nan Eilean - "Iron Road to the Isles") is a railway line linking the ports of Mallaig and Oban in the Scottish Highlands to Glasgow in Central Scotland. The line was voted the top rail journey in th ...
from Helensburgh Upper to Fort William and
Mallaig Mallaig (; gd, Malaig derived from Old Norse , meaning sand dune bay) is a port in Lochaber, on the west coast of the Highlands of Scotland. The local railway station, Mallaig, is the terminus of the West Highland railway line (Fort William ...
, and from
Crianlarich Crianlarich (; gd, A' Chrìon Làraich) is a village in Stirling council area and in the registration county of Perthshire, Scotland, around north-east of the head of Loch Lomond. The village bills itself as "the gateway to the Highlands". E ...
to
Oban Oban ( ; ' in Scottish Gaelic meaning ''The Little Bay'') is a resort town within the Argyll and Bute council area of Scotland. Despite its small size, it is the largest town between Helensburgh and Fort William. During the tourist season, th ...
. The system was also used on two other British rural lines: the East Suffolk Line, where the control centre was at
Saxmundham Saxmundham ( ) is a market town in Suffolk, England, set in the valley of the River Fromus about north-east of Ipswich and west of the coast at Sizewell. The town is bypassed by the main A12 road between London and Lowestoft. The town is ser ...
, and the
Cambrian Line The Cambrian Line ( cy, Llinell y Cambrian), also known as the Cambrian Main Line ( cy, Prif Linell y Cambrian) and Cambrian Coast Line ( cy, Llinell Arfordir y Cambrian), is a railway line that runs from Shrewsbury, England, westwards to Aber ...
from
Shrewsbury Shrewsbury ( , also ) is a market town, civil parish, and the county town of Shropshire, England, on the River Severn, north-west of London; at the 2021 census, it had a population of 76,782. The town's name can be pronounced as either 'Sh ...
to
Aberystwyth Aberystwyth () is a university and seaside town as well as a community in Ceredigion, Wales. Located in the historic county of Cardiganshire, means "the mouth of the Ystwyth". Aberystwyth University has been a major educational location in ...
and
Pwllheli Pwllheli () is a market town and community of the Llŷn Peninsula ( cy, Penrhyn Llŷn) in Gwynedd, north-western Wales. It had a population of 4,076 in 2011 of whom a large proportion, 81%, are Welsh language, Welsh speaking. Pwllheli is the pl ...
, where the control centre was at
Machynlleth Machynlleth () is a market town, community and electoral ward in Powys, Wales and within the historic boundaries of Montgomeryshire. It is in the Dyfi Valley at the intersection of the A487 and the A489 roads. At the 2001 Census it had a popul ...
.


The future

RETB is being gradually replaced with the new European in-cab signalling system,
ERTMS The European Rail Traffic Management System (ERTMS) is the system of standards for management and interoperation of signalling for railways by the European Union (EU). It is conducted by the European Union Agency for Railways (ERA) and is the o ...
. The Cambrian line was due to be changed over to the new system by spring 2010 but was delayed, being commissioned on 11 March 2011. The East Suffolk Line's system underwent life extension works in 2006, but was converted to conventional Track Circuit Block with axle counters in connection with increasing the service frequency to a point where the RETB could not have handled it. RETB was phased out on the East Suffolk Line after the last Ipswich-Lowestoft service arrived at Oulton Broad South on Friday 19 October 2012.


RETB Next Generation

Due to the loss of the Band III Sub Band 2 radio frequencies used by the NRN radio system from the digital TV spectrum reallocation the need arose for a system to replace RETB on two lines in Scotland - the West Highland Line and the Far North Line. The rugged terrain and light line traffic made it cost-prohibitive to install GSM-R for these areas and so a new radio system, with new base station and on-train equipment, was developed. This allows RETB to continue to operate on Band III Sub Band 1.
RETB NG Radio Electronic Token Block is a system of railway signalling used in the United Kingdom. It is a development of the physical token system for controlling traffic on single lines. The system is slightly similar to North American Direct Traffic ...
.


References

*Vanns, Michael A (1997): ''An Illustrated History of Signalling''. Ian Allan Publishing, Shepperton, England.


External links


Modernisation of the Cambrian Lines
includes discussion on a practical application of RETB.
Comms Design Ltd - System developer for RETB Next Generation
{{Railwaysignalling Railway signalling block systems