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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

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 only have a single 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 heritage railways and branches of national networks. The main problem with such a scheme is that it is only suited to a completely isolated piece of single track line. Where the section has to be integated into a larger railway system, it is completely impractical.

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 traverse the single line section. That object is known as a token and is identified as to which single track section it belongs.

Forms of token

Tokens have existed in a variety of physical forms:

  • staff
  • tablet
  • ball
  • key


Token systems

Token only

The token system was developed in Britainmarker 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. 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.

Staff and Ticket

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; for example in the circumstances of the Armagh rail disastermarker of 1889. Later, adoption of the electric telegraph system enabled a form of block working to be implemented.

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

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. These instruments are connected together electrically, and one token can be removed from either instrument provided that both signalmen co-operate in agreeing to the release. When a token is "out" a second token cannot be removed, but when the token is put into either instrument, a token can then be removed from either instrument. (There are variations on this sequence of events.)

By this means, it was ensured that at any one time, only one token was available to be issued to a driver. Tokens belonging to adjacent sections have different configurations to prevent them being inserted into the wrong instrument.

Collection of the token

Passing a miniature staff between station and train, with the use of a hoop


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, the train must stop for the token exchange.

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.

Automatic exchange

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.

Electronic token systems

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 a 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.

Tokenless block

This is not a token system, as the engine driver does not take possession of any form of token. Instead, 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. Indian Railways use this system especially in areas where there are double lines (two sets of rail track). A system Single Line Tokenless Block system is also in place for operations in single line routes. 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.

The timetable

This was another system that avoided the use of a token that was used on American railways during the 19th and early 20th century. It relied heavily on engine drivers knowing where other trains were and thus it was entirely dependent on trains adhering to the published timetable. There were mechanisms in place to communicate disruptions to engine drivers to avoid conflicting movements. It worked well on the lightly loaded American railways of the period, but would be entirely unsuitable for a more modern busy railway with numerous opportunities for service disruption.

The train arriving first at a passing place where it was known that a train was coming the other way was required to await the passing of the other train. There was a system that allowed two (or more) trains to pass over the same track section in the same direction. The first train carried two green flags (two green lights at night) on the cow catcher, and the driver gave 8 blasts on the engine whistle as he passed the stationary train. The stationary train driver was required to reply with 8 blasts on his whistle. The first train was required to stop if the reply was not received and the driver had to ensure that the stationary train was aware of the following train.

Variations

Intermediate block posts

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 1876marker. 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

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.

Working examples of this scheme may be found at:
: Between Bridgnorthmarker and Highleymarker (via Hampton Loademarker)
: Between Highleymarker and Bewdley Northmarker (via Arleymarker)
: Between Bishops Lydeardmarker and Willitonmarker stations (via Crowcombe Heathfieldmarker)
: Between Minfforddmarker and Tan-y-Bwlchmarker (via Rhiw Goch)
: Between Wirksworth station yard and Duffield station
: Between Wirksworth station and Ravenstor station on the Ravenstor 1 in 27 incline


Unattended operation

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 ) and the Liskeard to Looe line in Cornwallmarker. Here the train guard not only operates the Tyer's No.9 electric token machine 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 both the staff and the electric token 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

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

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.

Present day use

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 and Stranraermarker in south west Scotlandmarker. 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 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 Melbournemarker, 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 Victoriamarker, 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.

Other names

Various railways use different names for the same things:

New South Wales

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


See also



References

  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. Railway Group Standard GK/RT0051, page D1
  5. NSTR Signalling www.railsigns.co.uk; retrieved 2009-03-04
  • Vanns, Michael A (1997): An Illustrated History of Signalling. Ian Allan Publishing, Shepperton, England.



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