Token (railway signalling)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
A token being offered by a signalman on the Keighley and Worth Valley Railway
The moment the train driver picks up the next key token from the hands of the station master at the Bukit Timah Railway Station in Singapore moments after he had dropped off the previous token. This happened whilst the train was still fast moving.

In railway signalling, a token is a physical object which a locomotive driver is required to have or see before entering onto a particular section of single track. The token is clearly endorsed with the name of the section it belongs to. A token system is used for single lines because of the very much greater risk of serious collision in the event of irregular working by signalmen or traincrews, than on double lines.

Principle[edit]

Examples of single line tokens: Tablet on left, key token on right

The operation of a bidirectional single track line has obvious problems, the most serious of which is the possibility of two trains traversing the line travelling towards each other, both drivers unaware that the other is using the line. The simplest method of controlling such a line is to have only one engine operational, on the basis that a single train cannot collide with itself, and in the absence of another engine, there is nothing else for it to collide with. Such a system is known as "one engine in steam". Such schemes were used, and indeed still are used on some branches of rail networks, and on heritage railways. The main problem with such a scheme is that it is best suited to a completely isolated branch of single track line. Where the section has to be integrated into a larger railway system, it becomes exceptionally limiting in the level of operations that it allows, and the opportunity for a mistake to be made, and an ensuing accident to occur, is high.

Instead, rather than rely on a single engine, reliance is placed on having a single physical object available for the single track section and ruling that only if an engine driver is in physical possession of that object, is he permitted to enter the single line section. That object is known as a token and is marked to indicate to which single track section it belongs.

Forms of token[edit]

Tokens have existed in a variety of physical forms:

  • staff
  • tablet
  • ball[1]
  • key

Token systems[edit]

Token only[edit]

The token system was developed in Britain in the 19th century, to facilitate safe working of single-line railways. If a 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.

One Train Only token used in Indian Railways

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 is usually literally a wooden staff with a brass plate stating the two signal boxes between which it is valid.

In UK terminology, this method of working on simple branch lines was originally referred to as One Engine in Steam (OES), and later One Train Working (OTW). However the system was used on long through lines as well; R H Dutton, Chairman of the London and South Western Railway explained in 1876 the slow journey time between Exeter and Plymouth by saying, "the cause of the delay is the stopping at every station on the staff system. That really does cause a great delay because if the staff is not there, the train must stop while a man is sent on a horse to get it [from the other end of the section]"; quoted in Williams.[2]

Staff and Ticket[edit]

Using only a single token does not provide convenient operation when consecutive trains are to be worked in the same direction. The simple token system was therefore extended: if one train was to be followed by another in the same direction, the driver of the first train was required to be shown the token, but not take possession of it (in theory he was supposed to physically touch the token, but this was not strictly followed). He was given a written authority to enter the single line section, referred to as the ticket. He could then proceed, and a second train could follow. In the earliest days the second train could proceed after a designated time interval, as on double lines at the time. However, following the Armagh rail disaster of 1889, block working became mandatory.

Seeing the train staff provided assurance that there could be no head-on collision. To ensure that the ticket is not issued incorrectly, a book of numbered tickets is kept in a locked box, the key to which is permanently fastened to the token, or is the token. In addition, the lock prevents the token being removed until the ticket box is closed, and it cannot be closed unless the book of tickets is in the box. Once a ticket is issued, its number is recorded in a Train Register book, and the token is locked in a secure place. This system is known as staff and ticket.

In a variation on this principle, called divisible train staff, a section of the token referred to as the ticket portion was designed to be removed and handed to the driver instead of a paper ticket.

Electric token[edit]

Electric staff instruments manufactured by Webb and Thompson
Neale's token instrument manufactured by Westinghouse Brake & Signal Co.

The staff and ticket system was still too inflexible for busy lines, as it did not allow for the situation where the train intended to carry the actual token was cancelled or running very late. To provide for this, the electric train token system was developed. Each single-line section is provided with a pair of token instruments, one at the signal box at each end. A supply of identical tokens is stored in the instruments, which are connected by telegraph lines. A token can be removed from one instrument only if both signalmen co-operate in agreeing to the release. Once a token has been removed, another cannot be removed until the token which is "out" is replaced in either instrument. (There are variations on this sequence of events.) By this means, it can be ensured that at any one time, only one token is available to be issued to a driver. Tokens belonging to adjacent sections have different configurations to prevent them being inserted into the wrong instrument.

Nevertheless, in the Abermule train collision in 1921, lax working procedures allowed the safeguards provided by the electric token system to be circumvented; a driver was handed a token for the wrong section, and proceeded on the mistaken belief that the token was correct. To prevent this, it became a requirement in the UK for the signals controlling entry to the single line section (starting or section signals) to be locked at danger unless a token has been released from the relevant token instrument.

Collection of the token[edit]

In a basic railway situation, the token can be collected personally by the driver at the start of his work on a branch line, and surrendered by him at the end of his work there.

Where the single line section is part of a through route, then it is likely that each passing train would require to surrender and collect a token at each token station. Where the trains stop at every station this is a convenient arrangement, but where some trains run through without requiring to make a call, it was necessary for the signalman to exchange tokens with the fireman (in the case of steam trains) as the train passed at slow speed. In the case of driver-only operated trains, a dead-mans hold over button was provided, so the driver could exchange the token without the emergency brake being applied.

A large staff could be handed over without any special apparatus, but if the system in use employed miniature staffs, tablets or key tokens, these were usually placed in a leather pouch attached to a hoop, and the fireman could put his arm through the hoop held up by the signalman, and vice versa as the locomotive ran past. In UK practice the permitted speed for this was 15 mph in daylight, but there are stories of drivers anxious to make up lost time when running late, and passing the exchange point at much higher speeds; bruised upper arms were common among signalmen and firemen on such lines.

Fixed token exchange apparatus was used on some railways. Trackside equipment was fitted near each signal box to hold the pouch containing the token and to receive the token pouch that was being given up.[3]

Automatic exchange[edit]

Certain railways developed mechanical systems that enabled faster handover, using catcher devices that could be extended from the locomotive cabside just before the train passed the exchange point and which automatically retracted clear after the actual exchange. These enabled handover speeds of 40 mph; such a system was the Whitaker system on the Somerset & Dorset Railway, and the Manson system on the Great North of Scotland Railway. When the Aberdeen to Inverness passenger service was converted to diesel multiple unit operation in the late 1950s, the train-borne equipment was fixed adjacent to the train guard's compartment, and he was responsible for managing the mechanical handover; a special buzzer code enabled him to confirm to the driver that the correct token had been successfully received. Mechanical staff exchangers were also used where trains did not stop on the single line sections of the Main South, Main North and North Coast lines of the New South Wales Railways in Australia.These were fitted to both steam and diesel locomotives.

Electronic token systems[edit]

Developments in electronic systems have led to the development of electronic token systems. Trains are able to run over consecutive single-track sections, with the whole operation being controlled from a single central control room. Every train carries a special electronic unit that receives and sends an encrypted block of data which represents the token. The system is designed such that the control centre can only issue one token for any particular section until it is returned. Trains cannot send tokens to each other. This system allows the whole line to operate without any further signalling personnel. The system has operated without major incident.

Variations[edit]

Intermediate block posts[edit]

In certain circumstances it was convenient to shorten the single line sections by providing an intermediate signal box equipped with token instruments without providing a passing loop there. This was done if there was, for example, an important siding connection at the intermediate location. It also enabled following through trains to run at closer headways, but did not facilitate opposing movements.

Because of the greater risk of collision in the event of irregular working, the practice was deprecated in the UK, although some examples did exist for example at Beddington Lane on the Wimbledon - West Croydon line before resignalling. Usually in such cases special interlocking was provided between the two instruments at the intermediate signal box to ensure that trains could not be accepted from opposing directions at the same time.

A disaster at such an intermediate location occurred on the Somerset & Dorset Joint Railway at Foxcote, near Radstock, in the Foxcote collision of 1876. This occurred before the S&DJR was equipped for token working and was relying on block instruments only - a catalogue of errors led to two passenger trains entering the same section from opposite ends.

Long section working[edit]

In double line working, at times when traffic is light it is convenient to "switch out" an intermediate signal box, allowing the signal boxes on either side to communicate directly for train control. On single lines this is more complicated because of the train tokens being identified with single line sections, but the difficulty can be overcome by some form of long section working.

A simple system used separable train staffs which fit together when intermediate block posts are closed, so that a driver receives the train staff for two or more consecutive sections from the first signalman. An alternative system employs special long-section token systems; when long section working is to be instituted, all the short section tokens must be in their respective instruments; by switching to the long-section method, tokens for the long section can then be obtained in the ordinary way. Obviously all the long-section tokens must be restored before the normal working can be resumed.

Unattended operation[edit]

Token instruments can be arranged for unattended operation, when they are operated by the train crew at intermediate crossing loops or at the terminus of the line. This system is widely found in Australia, where traffic density on many lines is low.

In the UK it is known as the "No-signalman key token system". Examples on the UK national network are the North Devon Line, where the system was brought into use on December 1, 1987, the Heart of Wales Line (commissioned in 1986[4]), the Matlock branch in Derbyshire and the Liskeard to Looe line in Cornwall. Here the train guard not only operates the Tyer's No.9 electric token instrument controlling the upper section of the branch, but operates the points as well. The lower section is operated on the "One Engine in Steam" principle with a simple wooden staff. Possession of the staff is required to unlock the ground frame controlling the points at Coombe Junction, where the two sections meet. There is no other signalling on the branch except to control entry and exit to and from the main line.

Token interlinking[edit]

After early experience with token systems, it became customary for the starting signal at token stations to be interlinked with the token instrument; on withdrawal of a token, the starting signal lever was released for one pull.

Sometimes an intermediate siding is provided on the single line section, and the token itself, or a key fixed to the end of it, unlocks the points for shunting there. The token is locked in the apparatus there, and the driver cannot retrieve the token until the points have been set to the through running position and locked again. In special situations where the sidings at the intermediate location are extensive, the equipment is arranged for the shunting train to be put wholly inside the sidings, clear of the main line; in this situation an intermediate token instrument can be provided, enabling the driver to surrender the token so that normal through working can take place on the single line while his train is at the sidings.

A corresponding arrangement sometimes applied where permanent way maintenance was carried out by motorised trolley. Usually this used special "occupation key" instruments which were interlocked with the normal token instruments and provided at intermediate places where the trolley might be off-tracked (or stored overnight).

Working by pilotman[edit]

A variation of the token system is working by pilotman, where the place of the token is taken by a person who is designated the pilotman. This system is instituted if there is a failure of the token apparatus, or on double lines when one line is blocked and all the traffic in both directions is to be worked over the other line. The pilotman (identified by a red armband with "PILOTMAN" in white letters) rides on the locomotive, or if another train is due to follow, the pilotman must personally instruct the driver to proceed through the section. The signalman must not pull the starting signal off until instructed by the pilotman to do so. The pilotman rides on the locomotive or in the driving cab of the last train to run in the same direction. Thus pilotman working is analogous to the "staff and ticket" system, described above, where the pilotman himself becomes the token and his verbal instruction is the equivalent of the ticket.

It is sometimes necessary to provide the pilotman with a personal locomotive to cater for disruptions to the service. In such a case the pilotman's locomotive is usually coupled to the front of the actual train, but practice may vary depending on local track layout, types of trains etc.

The use of a pilotman for such purposes pre-dates the use of tokens.[5]

Present day use[edit]

Until the late 20th century, the token system was standard on British single-track lines and it still remains on a number of lines there as well as elsewhere, such as the line between Girvan and Stranraer in south west Scotland. Traditional token systems are also in use on heritage railways in Britain, for example on the Mid Hants Railway and the West Somerset Railway which is fitted throughout with Tyer's electric token instruments.

The token system was in use on the Hurstbridge railway line, Melbourne, Australia between Greensborough and Eltham (Miniature Electric Staff) and Eltham and Hurstbridge (Train Staff and Ticket) until replaced by electronic signalling in early 2013. The Greensborough-Eltham section was abolished on 31 January 2013, along with half of the Eltham-Hurstbridge section, as far as Diamond Creek. The final Diamond Creek-Hurstbridge section was abolished on 22 March 2013.

Puffing Billy Railway, in Melbourne, Victoria has used a staff and ticket system since it originally opened from Upper Ferntree Gully to Gembrook. The current line from Belgrave to Gembrook has permanent staff stations at Belgrave, Menzies Creek, Lakesideand Gembrook. A temporary staff station exists at Emerald town to allow trains to pass at Emerald on busy days. For the Emerald temporary staff to be activated, the Menzies Creek - Lakeside staff is required to be locked away at Menzies Creek. A similar situation occurs with Cockatoo station, whereby for it to be enacted as a Temporary Staff Station, the Lakeside – Gembrook staff is required to be locked away at Lakeside.

The token method of working is sometimes still used for temporary situations such as through engineering works or where the signalling system has yet to be provided. In December 1981, a new underground line was opened in Melbourne, Australia which provided a circular service around the city's central business district. Although normal services were not to begin for some time, for two months special services operated on Sundays to allow people to try the new line, and for this period the line operated with a train staff, although there was no provision for tickets to be used.

A very unusual token working was instituted on the line between Pakenham and Traralgon in Victoria, Australia for several months in 2006 whilst the line was being upgraded. During this period, the line was closed during the day, but opened each night to allow a few goods trains through. The line is double track between Pakenham and Moe (except for a short single track section). Three staffs were provided for the 100 km length, one each for the sections Pakenham—Warragul, Warragul—Moe, and Moe—Traralgon. The first two of these are partly or totally double-track sections, but the staffs in this case were applicable to both tracks, the effect being that only one of the tracks could be used at a time.

The token system is still regularly used present day on State Railway of Thailand system. Although most use occurs in regional areas, some use appears in the capital city, Bangkok, such as the Makkasan-Khlong Tan section etc.[6]

Other names[edit]

Various railways use different names for the same things:

New South Wales[edit]

  • Ordinary Train Staff (OTS)
  • Ordinary Train Staff and Ticket (OTST)
  • Electric Train Staff (ETS)

See also[edit]

References[edit]

  1. ^ Description of Neale's Ball Token Instrument
  2. ^ Williams, R A; The London & South Western Railway, volume 2; David & Charles, Newton Abbot; 1973; ISBN 0-7153-5940-1
  3. ^ Staff Exchangers in New South Wales Australian Railway History, August, 2004 pp318-319
  4. ^ NSTR Signalling www.railsigns.co.uk; retrieved 2009-03-04
  5. ^ Lascelles, T.S. (November 1959). "Controlling Traffic on Single Lines". In Cooke, B.W.C. The Railway Magazine (Westminster: Tothill Press) 105 (703): 746. 
  6. ^ http://m.youtube.com/watch?v=J5mvSgTFutA&feature=plpp
  • Vanns, Michael A (1997): An Illustrated History of Signalling. Ian Allan Publishing, Shepperton, England.