Safeworking Systems are a system of rules and equipment used to prevent conflict between trains.
Track is divided into Sections upon which only one one train is permitted. The end points of these sections may be a a place where trains may pass (such as a Station or Crossing Loop), a place where trains leave the main line (a Siding) or just a specially marked location (a Block Point).
Permission for a train to enter a section is refered to as an Authority. Each form of safeworking goes about the granting of these Authorities to trains in a different way.
Here is a short overview of the different types of safeworking used on the Victorian Railways.
Staff and Ticket was among the first safeworking systems to be developed. It is used on single lines. A single Train Staff is provided for each section. When trains are travelling across the section in opposite directions, each train takes the staff in turn, so ensuring that only one train is in the section at one time.
However, this single Staff presents problems when more than one train is proceeding in the same direction. To cure this problem, a Staff Ticket is used. The Train Staff is shown to the driver of the first train, then they are given a Ticket giving them authority to use the line. The second train is required to wait at the start of the section until a Line Clear message is received from the far end, then they are sent forward with the Train Staff (unless there is third train headed in the same direction, in which case another Ticket is given).
Double Line block is used on double lines where each track is used in only one direction. Authority to enter a section is given by fixed signals controlled by each departure station.
Special instruments are used by the signalmen at the departure and arrival stations to ensure the track between them is clear before a train is despatched along it.
Used on single rail lines, the Large Electric Staff method of safeworking divides a line into sections.
Authority for a train to travel in a section is given by a token known as the Train Staff. The Staff is a metal rod about 30 cm (12 inches) in length, and is marked with the name of the section where it is to be used.
Both ends of the section are required to be staffed for the operation of this system, with a series of bell codes needing to be exchanged between both ends before a Staff is given to the driver and a train despatched.
Train Staffs are stored in a Staff Instrument, with an instrument located at each end of the section. The instruments are connected so that only one Staff may be taken out of the system at one time. This interlocking, along with the procedures carried out before a staff is withdrawn, ensure that only one train is allowed in the single line section at one time.
Miniature Electric Staff is a derivative of the Large Electric Staff system.
The difference between the two systems are the Train Staffs themselves and the associated instruments. The Train Staffs in this system as smaller as the name suggests, being approximately 15 cm (6 inches) in length.
This system was developed due to difficulties in exchanging the larger Train Staffs. The smaller Staffs used in this system may be exchanged while the train is on the move; at low speeds by placing the staff onto a hoop to transfer from crew member to station staff, or at speeds of up to 115km/h via the use of specialised Automatic Staff Exchangers on the ground and on locomotives.
Composite Electric Staff is a variant of either Large or Miniature Electric Staff.
This system could be provided in a normal Electric Staff section, allowing a section to be divided up into one or more subsections. Each of these intermediate endpoints was known as a Block Point.
A special Composite Train Staff would be provided in the Instrument for the given section, the Staff being able to be separated into three portions. Each of these portions could be used to send a train forward into a section, provided all trains were in the same direction. Departure of trains at the start of the section, as well as the Block Points at the start of each subsection, was governed by telegraph or telephone communication by a qualified person.
Automatic Block System is used on double track lines where trains only operate in one direction on each. Authority to proceed along a line is given by fixed signals.
These automatic signals are provided at regular intervals along each track and show proceed unless the track ahead is occupied occupied, in which case they display a stop aspect. The signals behind then take on various caution aspects, depending on the configuration.
Automatic and Track Control is a tokenless form of safeworking, where the authority to enter a section of track given by signals located at the end of each section. ATC is used on both single and double lines, and permits traffic in both directions.
The signals at each end of the section are set up in such as way that only one may be set to 'proceed' at a time, hence only permitting one train in one direction into each section at a time. The signals remain at stop until the train has left the section.
A further feature of this system is the provision of intermediate signals inside each section. This allows multiple trains running in the same direction to be allowed into a single line section, but while still preventing a following train from becoming too closed to the train in front.
Centralised Traffic Control is another tokenless form of safeworking used for single lines.
All points and signals on a line are remotely controlled from one location, with the authority to enter a section of track given by fixed signals. As with ATC, intermediate signals can be used to divide up a section. A Train Controller at the remote location plans where trains will cross and sets the points and signals accordingly.
Section Authority Working is a uniquely Victorian safeworking system developed by V/line during the late 1980s and early 1990s. It was initially known as the Alternate Safeworking project. It is used on single lines and uses electronic tokens distributed by radio as the Authority for trains.
A special radio capable of displaying these Authorities is installed in each locomotive used over SAW tracks. Authorities are sent by the Train Controller at a remote location. The stand and end locations are noted in each Authority.
An additional feature of SAW is the remote control of points by radio. Using the above mentioned radios, special codes are entered in order to set a specific road into a crossing loop.
Train Order Working is a tokenless form of safeworking for single lines.
The Authority to enter a section of track is a Train Order issued by a Train Controller, either on a piece of paper, or dictated by radio or telephone. The Train Controller is required to ensure that the issued orders do not conflict.
Each Train Order details the train it is given to, and the start and end points of where the train is allowed to travel.
Yard Limits working is applied in non signalled locations such as yards and sidings.
No fixed signals apply, with trains only allowed to move if the track is clear, and are required to stop short of any other trains or wagons.