Token (railway signalling)
In railway signalling, a token is a physical object which a train driver is required to have or see before entering onto a particular section of single track.
For a larger railway system, it becomes exceptionally limiting in the level of operations that it allows, with the increased risk of mistakes being made, possibly leading to a collision.
Existing in a variety of physical forms, such as a staff, tablet, key, or ball, the object is marked to indicate to which single track section it belongs.
[2] The token system was developed in Britain in the 19th century, to enable safe working of single-line railways.
[3] If a branch line is a dead end with a simple shuttle train service, then a single token is sufficient.
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.
Once a ticket was issued, its number was recorded in a Train Register book, and the token was locked in a secure place.
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.
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 their 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 (24 km/h) 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.
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.
On the Victorian Railways automatic staff exchangers survived on the North Eastern, Western, and Geelong-Ballarat lines until as recently as the late 1980s.
On the South Australian Railways, auto staff exchangers were used on the former broad-gauge line between Adelaide and Port Pirie.
Every train carries an electronic unit that receives and sends an encrypted block of data which represents the token.
This system allows the whole line to operate without any additional signalling personnel, and has functioned without major incident.
Conventional "trapped key" pin tumbler locks (held in fixed position by solenoids) are mounted in key-release units set up at each end of controlled single line.
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.
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.
Possession of the staff is required to unlock the ground frame controlling the points at Coombe Junction, where the two sections meet.
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 Puffing Billy Railway in Melbourne, Victoria, has used a staff and ticket system since it was originally opened from Upper Ferntree Gully to Gembrook.
In December 1981, a new underground line was opened in Melbourne, which provided a circular service around the city's central business district.
Although most use occurs in regional areas, some use appears in the capital city, Bangkok, such as the Makkasan to Khlong Tan section etc.
The electric staff instruments manufactured by Webb and Thompson shown in the picture above are in use on the Buenos Aires (Constitución Station) to Mar del Plata line (Ferrocarril Roca) in Argentina, as of 2019.
In Malaysia, signaling token signs are still used on the KTM East Coast Line between Gemas and Tumpat.
Similarly, the Gemas Station Master needs to pass a key token for trains bound for the East Coast.
The final token exchange normally happens at Tumpat and Gemas but this also happens at Kuala Lipis and Dabong as these two stations are the terminus of some Eastern Shuttle (SH) train services.
This system was officially abolished on KTM's West Coast Line following the completion of the Ipoh - Padang Besar Electrified Double Track Project in 2014.
