Glossary of Terms


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Obscuration
A situation where there is an interruption of the driver's line of sight to an element. total obscuration occurs when the entire surface area of the element is hidden from the driver's view. Partial obscuration occurs when part of the surface area is hidden from view.

Preferred
Disciplines: Operations
Obstacle Deflector
An extension of vehicle body underneath the headstock at a cab end to deflect large obstacles from the track.

Non-preferred
Disciplines: Rolling Stock
Refer 'cow-catcher'.
Alternative
Disciplines: Rolling Stock
Obstruct
To make a line unsafe for the passage of rail traffic.

Preferred
Disciplines: ALL Disciplines, Operations
Obstruction
Any defect in the track or track formation, or obstacle on, above or adjacent to the track which will prevent the safe passage of trains.

Preferred
Disciplines: ALL Disciplines, Operations
Occupancy
Presence of rail traffic or track workers on track.

Preferred
Disciplines: ALL Disciplines, Operations
Occupancy Authority
A formal authority that allows occupancy of a portion of track by rail traffic or for work on track.

Preferred
Disciplines: Train Control, Operations
Occupation Crossing
Level crossing provided for a private roadway.

Preferred
Disciplines: ALL Disciplines
Occupied
A track section having any part of a train present upon it.

Preferred
Disciplines: Train Control, Operations
Occurrence
A general term for accidents and incidents which lead to injury or loss, or which are considered by the responsible authority to have the potential to compromise safety.

Preferred
Disciplines: ALL Disciplines
OCS
One Control Switch


Disciplines:
Off (aspect)
A proceed aspect in a colour light signal, or the arm of a semaphore signal or disc signal inclined at 45 degrees or more, or distant signal other than at its most restrictive aspect.

Overseas
Disciplines: Train Control
Off And On Signal Proving
Checking whether the signal is 'off' (open) or 'on' (closed).


Disciplines:
Office Of The National Rail Safety Regulator (ONRSR)
Office of the National Rail Safety Regulator

Preferred
Disciplines: ALL Disciplines
Offset (curve)
The distance from the centre of a chord to the running edge of a curved rail.

Preferred
Disciplines: Infrastructure
Offset Couplers
Automatic couplers where there is a vertical mismatch between the centreline of the coupling head and the centreline of the coupler shank.

Preferred
Disciplines: Rolling Stock
OIS
Operator Interface Station


Disciplines:
OL
Overlength Train


Disciplines:
On Or Near The Track
The space within 3 metres of the nearest rail when measured horizontally and at any level above or below the rail when measured vertically, unless in a safe place.

Preferred
Disciplines: ALL Disciplines
Refer to Danger Zone.
Alternative
Disciplines: ALL Disciplines
Related Term: Danger Zone
On Time Running
Measures the proportion of train trips which arrive within a given time of the scheduled arrival time.

Preferred
Disciplines: ALL Disciplines, Operations
On Track Machine (or On Track Vehicle)
Any power operated, self-propelled, flange wheel mounted maintenance machine or recorder vehicle, excluding road/rail vehicles and other small machines placed on and off track by hand or lifting equipment on site, such as re-sleepering plant.

Preferred
Disciplines: Rolling Stock, Infrastructure
On-site Test
These are tests using signalling power supplies of equipment and circuits installed in signalling structures with the track side equipment connected.

Preferred
Disciplines: Electrical
One Control Switch (OCS)
A type of route setting control panel having one switch (or other device) to control each route.

Regional
Disciplines: Train Control
One Spot
A repair facility designed to bring vehicles in need of repair to a central depot fully equipped with materials, handling equipment, tools and spares.

Regional
Disciplines: Rolling Stock
ONSR
Office of the National Rail Safety Regulator


Disciplines:
Open Ballasted Track
Track comprising rails, fastenings, sleepers and ballast. It does not include track comprising slab or embedded systems, or track on transom deck bridges.

Preferred
Disciplines: Infrastructure
Open Channel
A system which allows all radio users to take part in all conversations.

Preferred
Disciplines: Operations, Train Control
Open Circuit
The condition applying when a circuit is incomplete, as by the opening of a switch, or by the omission of a connection in the circuit, thus preventing current from flowing.

Preferred
Disciplines: Electrical
Open Level Crossing
Level crossing provided for a public roadway.

Preferred
Disciplines: ALL Disciplines
Open Standards
Standards publicly available and without constraint; equally available to all parties

Preferred
Disciplines: ALL Disciplines
Open Wagon (or Open Car)
A wagon with substantially vertical sides and ends, a flat floor and an open top, with or without doors in the side walls or floor.

Alternative
Disciplines: Rolling Stock
Operating Headway
The minimum spacing between trains, based on the specified maximum line capacity in trains per hour.

Preferred
Disciplines: Train Control, Operations
Operating Restriction
A restriction on the operation of rollingstock (e.g. reduced speed, axle load) to provide an appropriate level of risk in response to a specific infrastructure condition.

Preferred
Disciplines: Rolling Stock, Operations
Operational Specification
The technical specifications for rail operations on a route, including time of entry to and exit from the route, duration of use of the route, technical specification of rolling stock and rail infrastructure facilities, and safeworking standards.

Preferred
Disciplines: ALL Disciplines
Operational Use
The manner in which the equipment is used for the purposes of running trains.

Preferred
Disciplines: Operations
Operator Interface
The interface between the signalling system and the signaller which provides all the information and functionality needed by the signaller to control and monitor the signalling system.

Regional
Disciplines: Train Control
Operator Interface Station (OIS)
Any microprocessor based man-machine interface, typically any graphic user interface (GUI) using a keyboard, mouse and any array of visual display units (VDU's) to form a workstation for the purpose of train control.

Regional
Disciplines: Train Control, Electrical
Operator's Representative
A person authorised by an Operator to act on their behalf.

Preferred
Disciplines: ALL Disciplines
Opposing Train
Any train other than a following train which, if it continued beyond a nominated signal, would cross over or occupy the same track as another train.

Preferred
Disciplines: Train Control, Operations
Organisation
A Rail Infrastructure Manager or an operator, or a person or a body that is both Rail Infrastructure Manager and operator.

Preferred
Disciplines: ALL Disciplines
OSS
Overspeed Sensor System


Disciplines:
An 'overspeed sensor system' as applied to a TPWS.
Alternative
Disciplines: Operations
OTSI
Office of Transport Safety Investigations (NSW)


Disciplines:
Abbreviated term for 'Office of Transport Safety Investigations' (NSW).
Alternative
Disciplines: ALL Disciplines
Out Of Gauge Loads
A vehicle load that does not conform to the relevant loading outline.

Preferred
Disciplines: Rolling Stock, Infrastructure
Out Of Gauge Rolling Stock
Any vehicle that does not conform to a reference rolling stock outline applicable to a particular route.

Preferred
Disciplines: Rolling Stock
Out Of Use
Non-operational equipment that is still connected to the infrastructure.

Preferred
Disciplines: Infrastructure, Operations
Outer Home Signal
An outer home signal is a controlled signal which controls the movement of trains over the portion of line between that signal and the next signal in advance where a risk may only exist under certain circumstances. For example, a risk may exist for an approaching train when another train is required to shunt back outside a home signal towards the outer home signal.

Regional
Disciplines: Train Control, Operations
Overhaul
Actions carried out at the end of the service period to return the item to a condition that should give reliable operation for a further full service period.

Preferred
Disciplines: Rolling Stock
Overhead Line Equipment
The structures and overhead equipment necessary for the traction power supply for electric rolling stock.

Preferred
Disciplines: Electrical
Overhead Supply
The supply of electric current to the overhead wiring system for traction purposes.

Preferred
Disciplines: Electrical
Overhead Traction Wiring Equipment
See Overhead Line Equipment.

Preferred
Disciplines: Electrical
Overheated Bearing
Any bearing visibly overheating, or running hotter than other bearings on same vehicle.

Preferred
Disciplines: Rolling Stock
Overlap
The overlap of a signal is an extension of a track circuit beyond a stop signal to provide a margin of safety beyond that signal. The overlap must be unoccupied and free of opposing signal locking before the signal is permitted to show a proceed aspect.

Preferred
Disciplines: Train Control, Electrical
Overlap Maintenance
If a choice of overlaps exists beyond a stop signal then the clearing of the signal in rear will lock any facing points in the overlap beyond the stop signal to prevent the operation of those points towards an overlap that is not free, or is occupied (running signals); overlap maintenance will maintain that locking when an approaching train has passed the signal in rear.

Preferred
Disciplines: Train Control
Overlap Span
An overlapping of the ends of two lengths of overhead line equipment, arranged in such a manner that the pantographs of electric trains can pass smoothly and without break of contact from one contact wire to the next over the same track.

Preferred
Disciplines: Electrical
Overlay
A detection device designed to detect the approach of a train in addition to the normal track circuit train detection is referred to as an overlay device.

Preferred
Disciplines: Electrical, Train Control
Overlay Track Circuit
A track circuit installed on a section of track over which one or more existing track circuits are operating. Overlay track circuits are usually audio-frequency systems, configured so that the main and overlay track circuits operate independently of each other. Normally used for detecting the passage of a train at or past a specific position.

Preferred
Disciplines: Electrical, Train Control
Overlength Train (OL)
A train is overlength if its length exceeds the holding capacity of a designated running track at a crossing station.

Legacy
Disciplines: Operations
Overview
A signalling diagram or display that shows the whole of the area being controlled, usually with reduced detail.

Overseas
Disciplines: Train Control