- Radio Electronic Token Block
Radio Electronic Token Block is a system of
railway signalling used in theUnited Kingdom . It is a development of the physical token system for controlling traffic on single lines.How it works
On arrival at a "token exchange point", the driver reports his/her position to the signaller by radio and requests the "token" for the next section of line ahead. If the signaller is in a position to do so, he/she will issue the electronic token applicable to the section ahead. Simultaneously, the driver must operate a button on apparatus in the cab to receive the token. The token is then transmitted to the train by radio. The
Solid State Interlocking 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 him/herself 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 distant 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 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 orinterlocking , 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 simple nature of the lineside infrastructure in RETB areas ended with the installation of the
Train Protection & Warning System .History
The genesis of the system was on the
Far North Line , a long, remote single-track line betweenInverness , Wick andThurso inScotland . This line was controlled by traditional electric token instruments at each station, but in January 1978 the signal telegraphpole route 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 es to the cabs of trains. The line selected for the trial was another remote and lightly-used Scottish line: the oldHighland Railway route fromDingwall westwards toKyle of Lochalsh . The contract was placed with Westinghouse of Chippenham, Wiltshire, and the system was brought into use on28 October 1984 , with the control equipment situated at Dingwall. ["The Register of Scottish Signal Boxes", F Alexander & E S Nicoll (1990).] 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 for theWest Highland Line from Helensburgh Upper to Fort William andMallaig , and fromCrianlarich toOban . The system is also used on two other British rural lines: theEast Suffolk Line , where the control centre is atSaxmundham , and theCambrian Line fromShrewsbury toAberystwyth andPwllheli .The future
RETB is now regarded by the rail industry as a redundant technology and is being gradually replaced with the new European in-cab signalling system,
ERTMS . [cite web
last =
first =
authorlink =
coauthors =
title =ERTMS National implementation plan
work =
publisher =Department for Transport
month =September | year =2007
url =http://www.dft.gov.uk/pgr/rail/Interopandstandards/europeanstandardisation/ertms
format =.pdf
doi =
accessdate =2008-01-03 ] The Cambrian line is due to be changed over to the new system by 2009. The East Suffolk Line underwent life extension works in 2006 however the RETB system is due for replacement by 2011. Another reason for the replacement of the system is due to the radio frequency licence expiring.External links
* [http://www.signalbox.org/branches/aj/index.htm Modernisation of the Cambrian Lines] ; includes discussion on a practical application of RETB.
References
*Vanns, Michael A (1997): "An Illustrated History of Signalling". Ian Allan Publishing, Shepperton, England.
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