A few railways developed mechanical systems that enabled faster handover, using catching devices that could be extended from the locomotive cabside just before the train passed the exchange point and which automatically retracted clear after the exchange. These enabled handover speeds of 64km/h (40mph). Mechanical staff exchangers were also used where trains did not stop on the single line sections. These were fitted to both steam and diesel locomotives.
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 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.
– 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. 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.
– Long Section Working
In double line working, at times when traffic is light it is convenient to close 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
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), 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
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.
The use of a pilotman for such purposes pre-dates the use of tokens.