Token (railway signalling)

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 names 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.

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, each driver 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, reliance is placed not on employing only one engine but 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 may they enter the single line section. That object is known as a token and is marked to indicate to which single track section it belongs.

Tokens have existed in a variety of physical forms:

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.

For convenience in passing it from hand to hand, the token was often in the form of a staff, typically 800 mm (31 in) long and 40 mm (1.6 in) 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.

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