Any person working on the actual track needs to take possession of that section of track so that no other rail vehicles can be sent there.

Possession is requested from the signaller who will hand over possession when appropriate.

In some cases the points or signals are formally booked out.

In all cases, the signaller applies physical or electronic measures to prevent rail traffic over affected areas.

A signalling system where trains are kept separated by the time on clocks.

Where timetables are used, trains should arrive and depart on a strict schedule that caters to all known movements. Where no timetables are used, trains are provided an amount of time to (sufficiently) clear the block before the next train could follow.

Success in this system depends on all clocks being accurately synchronised, trains not breaking down (or apart) and all trains travelling at a uniform (or sufficient) speed, and all train movements being known — none of which could be uniformly guaranteed.

See also block separation.

Tracks support the train and guide it. A track consists of two rails, attached to sleepers which are embedded into ballast.

In terms of train movement, a track is often referred to as a road.

A track circuit is used to prove vacancy of the track, not the presence of a train. Track-circuits are used in the operation and control of signalling equipment.

There are a number of types of track circuits in use but they essentially transmit a current through the rails to a receiver. If a train shunts the rails, the receiver reacts and the signalling equipment responds appropriately.

Is the vital state of a section of track being occupied by a train.

A faulty track circuit may suggest a train is occupying a section of track when there really is no train.

The system that provides power for electrified trains is known as the traction system.

Many metropolitan railways use overhead electrical conductors or line-side conductors to power the train network.

The most common type is the 25kV AC power as used in British Railways and also Queensland. However the Victorian and NSW metropolitan networks use 1500V DC.

Trailable points have mechanisms that are not damaged if a train makes a trailing move over an incorrectly positioned set points.

This is sometimes known as ‘running through the switch’ or 'splitting the points'. 

A set of points not able to be trailed are referred to as non-trailable points.

Train control is carried out in a train control centre (train operations centre).

Typically, a train controller decides when to intervene on a train's timetabled movement in response to incidents such as late running, accidents or a rolling stock/track maintenance requirements and advises the train controller.

A signal controller manipulates train movements to achieve the train controller's decision by remotely operating the signalling equipment in the field.

All decisions are only effected if the interlocking determines that the intervention is safe. The interlocking and the signalling equipment in the field are the safety-critical signalling system.

The system that relays vital and non-vital information is the signalling communications system.

Train Controllers manage the safe and efficient path of trains in a defined geographical area of responsibility.  They set priorities and:

• oversee signallers
• manage train services
• give authority for work to be conducted on tracks
• give authority for trains to proceed
• manage incidents by liaising with relevant operators and maintenance representatives
• respond to equipment failures and warning alarms
• give relevant information to other train controllers and signallers
• report breaches to relevant authorities
• maintain relevant network records and reports

See also signaller.

A system where train identification numbers are stored (often obtained off a stored timetable) and are displayed to signallers on their VDUs or display panels. Typically, the train identification number is shown with the position of the train, and it may also be shown with the route that has been set in front of that train.