Token (railway signalling)

In railway signalling, a token is a physical object given to a train driver to authorize them to proceed onto a particular section of single-track railway. The token system is a fundamental safety mechanism used on single lines to prevent collisions, ensuring that only one train occupies a section of track at any given time. This system is crucial because, without it, there would be no guarantee against two trains entering the same single-track section from opposite directions, leading to a head-on collision.

The token itself may take various forms, depending on the specific system in use. Common forms include staffs (sometimes referred to as “batons”), tablets, or even keys. Each token represents a specific section of single line.

The process typically involves the signaller or signalman at one end of the section obtaining the token before handing it to the driver of the train intending to enter that section. Possession of the correct token is the driver's authority to proceed onto the single line section. No train is permitted to enter the single-track section without the appropriate token.

After the train has cleared the single-line section, the token is returned to the signalling system, ready to be used again for another train travelling in either direction. Depending on the system design, tokens may be returned to the starting signal box manually or via a token instrument, which can electronically or mechanically manage the release of tokens and ensure that only one token for a given section exists at any time.

Different variations of token systems exist, including:

• Staff and Ticket: A variation where the staff is kept at one end of the section, and the driver receives a ticket as authorization, with safeguards to prevent multiple tickets being issued simultaneously.
• Electric Token Block: Systems that use electrical interlocking to control the release of tokens, providing increased safety and efficiency.

The token system, while effective, can be relatively slow and inflexible compared to more modern signalling systems. Nevertheless, it remains in use on many heritage railways and less busy lines worldwide due to its simplicity and inherent safety. More modern systems such as Centralized Traffic Control (CTC) offer increased capacity and automation but rely on complex technologies. The reliability and robustness of the token system have made it a longstanding and vital component of railway safety on single-track lines.