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NWR SR CH3 Eng

Signalling

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0% found this document useful (0 votes)

213 views39 pages

NWR SR CH3 Eng

Signalling

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KarimullaSk

We take content rights seriously. If you suspect this is your content, claim it here.

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Ref N

No: Gloossary
Issue No: 1.00
Issue date: Jannuary 2011

INS
STITUTIO
ON OF R
RAILWAY
Y SIGNA
AL ENGIN
NEERS
MINOR
M R
RAILWAY
YS SECTTION
GU
UIDELIN
NE ON

GLLOSS
SAR
RY OFF SIG
GNA
ALLING AND
A D
TE
ELEC
COM
MMUNICA ATIO
ONS
TERM
T MINO OLOGY
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 2 of 39

Record of Amendments
Issue Date Amendments
1.0 15/01/11 Original issue

Anyone who wishes to contribute additional items; or correct / amend any of the entries; or wants further
information may contact the IRSE Minor Railways Section Document Co-ordinator at mrsdc@irse.org or via
the IRSE Headquarters.

IRSE 2011
Uncontrolled when Printed
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 3 of 39
INTRODUCTION
This document defines the meaning of commonly used signalling and telecommunications terms to ensure
that each term is clearly understood and always used to convey the same meaning.
This section includes terms in common use within railway Signalling or Telecommunications engineering,
together with related railway operating and infrastructure terms. It is understood that this document cannot
be all encompassing for all regions but relates only to Signal and Telecommunications Engineering. The
Operations Department may have different understanding of the terms.
It also supplements other guidelines issued by the IRSE Minor Railway section.
The glossary is arranged in alphabetical order, with each entry shown in bold type. A word or group of words
in italic type refers to another entry providing further information.
Some entries simply cross-refer to other entries. These may be abbreviations or terms referring to the full or
more commonly used entry. Generally, the full definition is only given once.
The following have not been included;
a) Terms specific to the internal component parts of electronic systems or subunits, for example, CPU,
MPM, PPM. These are generic to many system types
b) Specific terms relating to specialised activities such as signal sighting.

Signal Names.

The use of signal names such as Home Signal and Starting Signal refer to current accepted practice.
Historically there have been regional variations of signal names, particularly for Home Signal, Inner Home
Signal and Outer Home Signal. Some of these variations are shown but it is not a complete list.

Anyone who wishes to contribute additional items or correct / amend any of the entries or want any further
information on this subject please contact the IRSE Minor Railways Section Document Co-ordinator at
mrsdc@irse.org or via the IRSE Headquarters.

TERM DEFINITION
ABSENCE SWITCH A switch which, when operated, allows a SIGNAL BOX to be
unmanned for a period by restricting the operation of some
equipment, such as alarms.
ABSOLUTE BLOCK A system of controlling trains, where (under normal operations) only
one train is allowed into a BLOCK SECTION at a time. Proof of a
section clear normally involves the observation of the train TAIL
LAMP by the SIGNALMAN.
ABSOLUTE POSSESSION See POSSESSION.
AC Alternating Current
ACCEPTANCE A block signalling term where a train is permitted to proceed towards
the accepting signal box. The block regulations provide for
circumstances under which a signalman may accept a train.
ACCEPTANCE LEVER See direction lever.
ACCOMMODATION LEVEL A private vehicular LEVEL CROSSING connecting land in the same
CROSSING ownership separated by a railway line.
ADVANCED STARTING SIGNAL In Block Signalling, a Stop Signal beyond the Starting Signal, and
worked from the same Signal Box. An alternative term for Section
Signal on the Western Region.
ADVANCED WARNING BOARD A sign incorporating a St. Georges Cross provided on the
(AWB) APPROACH TO certain open LEVEL CROSSINGs to inform the
driver to regulate the speed of the train in order to observe the
restriction of speed which applies over the crossing.
ADVANCE WARNING INDICATOR A sign provided on the approach to a permanent or temporary speed
(AWI) restriction board.
ALIGHT The internal illumination of signalling equipment.
ALPHANUMERIC ROUTE A Route Indicator that conveys its information by illuminated
INDICATOR alphanumeric characters. Designated standard and miniature
as a reference to size and readability.
ANNETTS KEY/LOCK A locking mechanism, often for unlocking a ground frame or other
equipment. The key may be held captive in an instrument or lock
which can be released from the controlling signal box.
ANNUNCIATOR An audible indicator, e.g. bell or buzzer.
ANTI-PRESELECTION The prevention of preselecting a signalling function before the
interlocking allows the function to be used.
APPARATUS CASE (OR A housing containing equipment which is normally intended for
CUPBOARD) outdoor use.
APPROACH CONTROL The restriction of the ASPECT of a SIGNAL to ensure that the driver
can comply with the TURNOUT SPEED or to control the speed of
the train for a SUBSIDIARY or SHUNTING SIGNAL.

TERM DEFINITION
APPROACH LOCKING The locking of any POINTS or a ROUTE from a SIGNAL, when the
driver has seen or may have seen a PROCEED ASPECT at the
signal. If the signal is replaced to danger, the approach locking
prevents the release of the route or points because it is possible
that the approaching train may be unable to stop.
APPROACH RELEASE An alternative term for APPROACH CONTROL.
APPROACH TO An alternative term relating to IN REAR OF.
APPROACH LIGHTING The lighting or illumination of a SIGNAL only on the approach of a
train. If no train is approaching, no light is displayed.
AREA OF CONFLICT A section of line BEYOND the SIGNAL at DANGER on which a
head-on, crossing or same direction converging collision with
another legitimately positioned train could occur in the event of a
SPAD.
ASPECT Any valid visual indication of a SIGNAL as displayed to the driver.
ASPECT LEVEL (OR LOCKING) The level of INTERLOCKING required to be satisfied before a
SIGNAL can display a proceed ASPECT.
ASPECT SEQUENCE The order of the displayed ASPECTS to give the driver information
about the aspect of the SIGNAL or signals ahead.
ASPECT SEQUENCE CHART A diagram showing the sequence of ASPECTs displayed at
successive SIGNALs.
ATTAINABLE SPEED The maximum speed that a train able to achieve at a location.
AUDIBLE WARNING An audible tone or bell that is sounded when the LEVEL CROSSING
protection system is activated.
AUTOMATIC BARRIER An AUTOMATIC LEVEL CROSSING equipped with HALF-
CROSSING LOCALLY BARRIERS and road lights at which the correct operation of the
MONITORED (ABCL) equipment is monitored by the train driver.
AUTOMATIC HALF BARRIER An AUTOMATIC LEVEL CROSSING equipped with HALF-
CROSSING (AHBC OR AHB) BARRIERS and road lights at which the correct operation of the
equipment is monitored by the Signalman.
AUTOMATIC LEVEL CROSSING A LEVEL CROSSING which is operated by the approaching trains
and is not normally INTERLOCKED with protecting SIGNALS.
Road light signals are provided. HALF-BARRIERS may be
provided, depending on the type of automatic crossing.
AUTOMATIC OPEN CROSSING An AUTOMATIC LEVEL CROSSING equipped with road lights at
LOCALLY MONITORED which the correct operation of the equipment is monitored by the
(AOCL) train driver. BARRIERS are not provided.
AUTOMATIC OPEN CROSSING An obsolescent type of AUTOMATIC LEVEL CROSSING, similar to
REMOTELY MONITORED an AHBC but without BARRIERS.
(AOCR)
AUTOMATIC SIGNAL A SIGNAL controlled by the passage of trains (normally TRACK
CIRCUITs). It does not require any action by the SIGNALMAN.
IRSE 2011
Uncontrolled when Printed
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 6 of 39

TERM DEFINITION
AUTOMATIC TRAIN A system used to transmit the state of the signalling to the cab of a
PROTECTION (ATP) train. The train borne equipment is operated by the system only
in the event of the driver not controlling the train in accordance
with the information displayed
AUTOMATIC WARNING SYSTEM A system that provides audible and visual warnings to the driver on
(AWS) the APPROACH TO SIGNALS, certain Level Crossings and
some speed restrictions.
AUXILARY TOKEN INSTRUMENT A supplementary TOKEN INSTRUMENT, usually located at the end
of a token section but remote from the signal box. It may also
include the same BLOCK SECTION release controls as the main
instrument.
AXLE COUNTER A TRAIN DETECTION SYSTEM using track mounted equipment
which counts the number of axles into and out of a TRACK
SECTION.
BACKDRIVE An additional drive connected to the SWITCH RAILS of a set of
POINTS at a position closer to the CROSSING than the switch
tips.
BACKLIGHT An aperture provided at the rear of certain SIGNAL lamps to enable
the SIGNALMAN to see that the signal is ON and ALIGHT.
BACKLOCKED The condition of a lever which is locked to prevent its return to the
fully NORMAL position.
BANNER REPEATING SIGNAL A signal that provides the driver with preliminary information about
the aspect a SIGNAL. Usually provided where sighting of the
main SIGNAL is inadequate.
BARRIER (LEVEL CROSSING) A device pivoted at the side of the carriageway (road) which is
lowered when required to close the carriageway (road) to road
users.
BARRIER CONTROL PEDESTAL A separate operating console located in view of the LEVEL
CROSSING under operation.
BARRIER PEDESTAL A structure supporting the BARRIER and containing the operating
equipment.
BARRIER SKIRT The lattice (metal or plastic) attached to the BARRIER at some full
barrier crossings, designed to reach the floor when the barriers
are in the Down position. It enables the railway to be fenced off
when using full barriers.
BARRIERS UP INDICATOR An indicator provided beyond a TMO crossing to indicate that the
barriers have raised after the passage of a train.
BARROW CROSSING A crossing (often at the end of a platform) for staff use. Protection, if
provided, is by means of white lights that are LIT when it is safe
to cross.
BAY PLATFORM A generally shorter platform that serves a dead-end line.

TERM DEFINITION
BERTH TRACK CIRCUIT The TRACK CIRCUIT that is immediately on the APPROACH TO a
SIGNAL.
BEYOND An alternative term relating to IN ADVANCE OF.
BIASED A term used in connection with relays where the relay will return to
the original position see also POLAR BIASED
BI-DIRECTIONAL LINE A line on which the signalling permits trains to be signalled normally
in either direction. See BI-DIRECTIONAL SIGNALLING.
BI-DIRECTIONAL SIGNALLING Signalling which permits trains to be signalled normally in either
direction on a RUNNING LINE.
BLINDER A plate that covers a BACKLIGHT to enable the SIGNALMAN to see
that a SEMAPHORE SIGNAL is operating correctly.
BLOCK BELL A single stroke bell for communicating between BLOCK POSTs,
SIGNAL BOXes, etc. by means of a code of audible signals.
BLOCK INSTRUMENT The equipment in a BLOCK POST for the operation of BLOCK
SIGNALLING on a double line of railway or for TOKENLESS
BLOCK working on a single line of railway.
BLOCK JOINT See INSULATED BLOCK JOINT.
BLOCK OVERLAP An alternative name for CLEARING POINT.
BLOCK POST A location at one end of a BLOCK SECTION, usually, but not
always, a SIGNAL BOX.
BLOCK SECTION The section of line between the SECTION SIGNAL of one BLOCK
POST and the HOME SIGNAL of the next block post in the
direction of travel.
BLOCK SHELF A shelf, normally located above the LEVER FRAME, to hold
equipment associated with the SIGNALLING SYSTEM and
control of the line
BLOCK SIGNALLING A system of controlling trains defined by BLOCK SECTIONS. See
also ABSOLUTE BLOCK and PERMISSIVE BLOCK.
BLOCK SWITCH Equipment located in a SIGNAL BOX which allows the signal box to
be closed but maintain the correct operation of through trains.
The BLOCK SECTION each side of the closed signal box will be
operated as one section.
BLOCKING BACK Term used when a train or SHUNTING MOVEMENT is allowed to
occupy the line within the CLEARING POINT, or outside the
HOME SIGNAL.
BLOCKING BACK (LEVEL The formation of stationary or slow moving road traffic over a LEVEL
CROSSINGS) CROSSING causing an obstruction to the line.
BONDING PLAN A longitudinally scaled or dimensioned track layout plan showing
both rails, insulated rail joints, track circuit cabling and associated
equipment. See also IRJ PLAN.

TERM DEFINITION
BONDS, BONDING Generic terms for the electrical connections within a track circuit.
BOOM An alternative term for barrier.
BOOM LIGHTS Small red lights provided along the barrier that are LIT when the
barrier is dropping or is down.
BOX TO BOX CIRCUIT Direct Line running from one signal box to the next.
The term may have described an omnibus circuit calling in at each
signal box along a line of route.
BRACKET SIGNAL A structure that incorporates an overhang, normally to position a
SIGNAL for sighting purposes. Can also be known as a
CANTILEVER SIGNAL.
BRAKING CURVE A graphical representation of the BRAKING DISTANCE of train in
relation to the gradient of the track, the braking characteristics
and speed of the train.
BRAKING DISTANCE The distance in which a train is capable of stopping in an emergency.
(EMERGENCY)
BRAKING DISTANCE (SERVICE) The distance in which a train is capable of stopping from a given
speed, at such a deceleration for a passenger train that the
passengers do not suffer discomfort or alarm.
BRIDLEWAY As path designated for used by horse and pedestrians.
BUFFER STOP A structure fixed at the end of a RUNNING LINE or SIDING to arrest
slow moving vehicles. See also STOP BLOCK.
BUFFER STOP LIGHTS The lights fixed to a BUFFER STOP.
CABLE ROUTE The course of the main signalling and power cables. Often the
cables are buried or laid in a protective covering.
CALLING-ON ROUTE A ROUTE that is provided to permit a train movement into an
OCCUPIED section.
CALLING-ON SIGNAL A SUBSIDIARY SIGNAL used for movements into an OCCUPIED
signal section.
CANT The difference in level between the rail head centres of a curved
track.
CANTILEVER A structure that incorporates an overhang, normally to position a
SIGNAL for sighting purposes. Can also be known as a
BRACKET SIGNAL.
CASCADED CUT SECTION An arrangement for a CUT SECTION TRACK CIRCUIT in which the
TRACK CIRCUIT RELAY of one section is used to control the feed to the next
section.
CATCH HANDLE The handle on a mechanical lever attached to a latch which holds
the lever in a specific position.
CATCH POINTS POINTS provided to derail vehicles running back on rising gradients
on a RUNNING LINE (see also TRAP POINTS).
IRSE 2011
Uncontrolled when Printed
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 9 of 39

TERM DEFINITION
CATERHAM LOCKING The NORMAL lie of points at a TERMINAL STATION that directs
potential runaway trains to avoid a head-on collision.
CATTLE-CUM-TRESPASS A device provided at a LEVEL CROSSING to deter animals and/or
GUARD pedestrians from straying on to the railway.
CAUTION An ASPECT which advises the driver that the next SIGNAL may be
at DANGER. See also PRELIMINARY CAUTION.
CB Central Battery
CB Line A telephone line where the power for the telephone is fed
from the central equipment and the normal method of calling is by
applying a telephone loop across the line.
CB Telephone Generally a telephone without a dial as used for
signal post telephones.
CHECK LOCKING An arrangement to prevent the full stroke of a lever in a LEVER
FRAME until such time as the apparatus controlled by that lever
has completed its movement. See also INDICATION LOCKING.
CIRCUIT CONTROLLER A circuit switching device containing a number of contacts, each of
which may be adjusted to make or break when operated by a
lever, SIGNAL or POINT.
CLAMP LOCK A point operating mechanism which locks the POINTS by directly
clamping the closed SWITCH RAIL to the STOCK RAIL.
CLEAR (A SIGNAL) To change a SIGNALs ASPECT from its most restrictive aspect to a
less restrictive aspect.
CLEAR (ASPECT) A COLOUR LIGHT SIGNAL that is displaying A PROCEED ASPECT
or a SEMAPHORE SIGNAL in the OFF position.
CLEAR (TRACK SECTION) The TRACK SECTION is clear of any train on a TRACK CIRCUIT or
a section is clear of axles.
CLEARANCE BAR A DEPRESSION (or lifting) BAR used to prove clearance usually
between converging ROUTES. Can also be found on diverging
ROUTES to prove a train has passed sufficiently clear of the
junction.
CLEARANCE POINT The minimum distance from POINTS and crossings at which TRACK
CIRCUIT boundaries may be positioned, to prove that a vehicle
on one track is in a position clear of a movement on an adjacent
track nominally 166 from the FOULING POINT for standard
gauge track
CLEARING POINT The point to which the line must be clear (with any POINTs in the
correct position) before a train can normally be accepted from the
BLOCK POST in rear.
CLOSURE RAIL A rail located between SWITCH and CROSSING components, cut to
a length to fit the requirements of the TURNOUT.

TERM DEFINITION
CO-ACTING SIGNAL An additional SIGNAL that is provided in exceptional circumstances
for sighting reasons. It displays identical aspects to the main
SIGNAL.
COLOUR LIGHT SIGNAL A SIGNAL that conveys its information by means of coloured lights.
COMMISSIONING The process of bringing into service including testing and hand over
of a product or system.
COMMON RAIL The rail of a single rail TRACK CIRCUIT that is electrically common
to one or more adjacent track circuits or forms the traction return
path. In non-electrified areas the common rail is bonded with
track circuit bonding. In electrified areas the common rail is
known as the traction return rail and carries the traction return
current. It is therefore bonded with traction return bonding.
COMPETENT PERSON A person who has the required knowledge and skills to carry out a
particular rule regulation, instruction or procedure.
COMPREHENSIVE (OR FULL) APPROACH LOCKING controls which will allow the immediate
APPROACH LOCKING release of approach locking if there is no train within the
SIGHTING DISTANCE of the outermost signal affected by the
approach locking.
CONCENTRATOR A telephone switchboard allowing the operator to answer or make a
call on any one of a number of incoming telephone lines.
CONDITIONAL LOCKING INTERLOCKING between two signalling functions which is
dependent on the state of a third signalling function.
CONFLICTING LOCKING INTERLOCKING between two signalling functions which require one
or more POINTS SET in opposite positions.
CONFLICTING MOVEMENTS Movements which would require two or more trains to occupy the
same portion of track over all or part of its length.
CONTROL TABLE A part of the signalling system specification that defines the detail of
the signalling controls and INTERLOCKING for each signalling
function, normally in tabular form.
CONTROLLED LEVEL A LEVEL CROSSING equipped with GATES or full BARRIERS that
CROSSING are Interlocked with protecting SIGNALS. ROAD TRAFFIC
SIGNALS may be provided. Additional barriers or WICKET
GATES for pedestrians may be provided.
CONTROLLED SIGNAL A SIGNAL that is controlled to its most restrictive ASPECT from a
SIGNAL BOX or GROUND FRAME.
CONVERSE LOCKING See RECIPRICAL LOCKING.
CORRELATION The comparison of the signalling equipment with the design records
to ensure that the two are in agreement.
CORRESPONDENCE The agreement of the INTERLOCKING with the DETECTED state of
a SIGNALLING FUNCTION.

TERM DEFINITION
COSHH Control of Substances Hazardous to Health. Legislation introduced in
1988.
COUNTER CONDITIONAL INTERLOCKING which prevents a condition, upon which other
LOCKING interlocking is dependent, from being bypassed.
CRANK HANDLE A portable handle for insertion in POINT MACHINEs to enable them
to be operated manually.
CREEP SIGNALS Alternative term for LOADING / UNLOADING INDICATORS.
CROSSING A fabricated portion of the track layout which enables the rails of the
two tracks to cross each other, while still providing support and
guidance for smooth passage of vehicle wheels.
CROSSING BOX An alternative name for a GATE BOX.
CROSSING KEEPER A person appointed at a GATE BOX to carry out the normal
operating procedure of a LEVEL CROSSING.
CROSSING TIME Time taken for a user to traverse the LEVEL CROSSING from the
decision point to a position of safety on the other side of the
railway. Crossing time includes time taken for the user to make
the decision to cross.
CROSSOVER Two TURNOUTS connected to form a continuous passage between
two parallel tracks. See FACING and TRAILING.
CUT SECTION (LINE CIRCUIT) The sectioning of line circuits to avoid exceeding the maximum
length allowed.
CUT SECTION (TRACK CIRCUIT) The splitting of a train detection section into two or more track
circuits to avoid exceeding the maximum length allowed. They will
be indicated as one track section in the signal box.
DANGER (ASPECT) An indication given by a SIGNAL to stop.
DEAD LOCKING Locking which is not conditional on any other locking.
DEFECTIVE SIGNAL A SIGNAL with a fault that affects its designed operation.
DEGRADED MODE CONDITIONS The state of the part of the railway system when it continues to
operate in a restricted manner due to the failure of one or more
components.
DELAYED YELLOW (ASPECT) A COLOUR LIGHT SIGNAL ASPECT to which APPROACH
CONTROL has been applied where speed must be reduced
before the next signal, e.g. WARNING ROUTE.
DEPRESSION BAR A metal bar so mounted alongside the rail that it is depressed by the
wheel flanges of a vehicle.
DERAILER A safety device attached to a rail, that when passed over in the
raised position, causes a derailment of a vehicle in an
unauthorised movement.
DETECTED (POINTS) Proved in the NORMAL or REVERSE position.
DETECTION The proof of the position of POINTS, either NORMAL or REVERSE.
IRSE 2011
Uncontrolled when Printed
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 12 of 39

TERM DEFINITION
DETONATOR A small disc-shaped audible warning device, placed on the rail head,
which explodes when a train passes over it. Used for emergency
or protection of the line.
DIAMOND CROSSING A crossing of two rail tracks.
DIRECT LINE A telephone that only connects the user to one pre determined
location.
DIRECT OPPOSING LOCKING INTERLOCKING between two ROUTEs in opposite directions for
which the lie of the POINTS is the same.
DIRECT TRACK LOCKING Locking of POINTS or FACING POINT LOCKs by a track circuit
indicated as OCCUPIED.
DIRECTION LEVER A non-TOKEN system of SINGLE LINE working usually requiring
continuous train detection through the section. Also known as
ACCEPTANCE LEVER block. Classified as a form of TRACK
CIRCUIT BLOCK working.
DISC SIGNAL A SHUNTING SIGNAL consisting of a small disc which rotates to
indicate a change of ASPECT.
DISCONNECTED SIGNAL A SIGNAL that has been adjusted to ensure that it only shows the
most restrictive ASPECT.
DISCONNECTION BOX A small equipment case containing cable terminations where circuit
disconnections can be made.
DISTANT BOARD A reflectorised sign that is the equivalent of a FIXED DISTANT
SIGNAL.
DISTANT SIGNAL (COLOUR A SIGNAL that will show a CAUTION or a PRELIMINARY CAUTION
LIGHT AREA) as its most restrictive ASPECT and operates automatically
dependant on the ASPECTs displayed at the next signal ahead.
DISTANT SIGNAL (MECHANICAL A SIGNAL that displays a CAUTION ASPECT as its most restrictive
AREA) and will only display a PROCEED ASPECT when all the stop
signals on the same route associated with a block post are also
displaying a PROCEED.ASPECT. See also SPLITTING
DISTANT signal. Can be either a colour light signal or a
mechanical signal.
DISTANT WARNING BOARD An alternative name for an ADVANCED WARNING BOARD.
DIVERGING ROUTE In the signalling of junctions, any ROUTE that diverges from the
fastest, main or straight.
DOG CHART An alternative name for LOCKING CHART.
DOLL A short post on a CANTILEVER, GANTRY or bracket, on which is
mounted one or more SEMAPHORE SIGNALs.
DOUBLE JUNCTION The point of junction of two double track routes. It comprises two
POINTS AND a DIAMOND CROSSING.
DOUBLE SLIP A combination of a DIAMOND CROSSING with four POINTS.

TERM DEFINITION
DOUBLE YELLOW (ASPECT) A preliminary CAUTION ASPECT displayed by a COLOUR LIGHT
SIGNAL informing the driver to expect the next MAIN SIGNAL to
be at SINGLE YELLOW.
DRAW AHEAD SIGNAL A POSITION LIGHT SIGNAL which functions as a CALLING-ON
SIGNAL or a SHUNT AHEAD SIGNAL.
DRIVERS EYE LEVEL The vertical distance between the drivers eyes when in the normal,
seated position, and the crown of the LEFT-HAND RAIL. (This
may be a nominal value, representative of several types of driving
cab and/or the variation in the population of drivers. Alternatively,
for a particular scenario, it may be a specific, measured value.
Unless special circumstances dictate, driving seats are assumed
to be adjusted vertically to their mid-position.)
DRIVERS LEVEL CROSSING An INDICATOR provided at certain types of LEVEL CROSSINGS to
INDICATOR indicate to the driver the state of the crossing equipment.
DRIVERS RED LIGHT A SIGNAL that is displayed to a train driver approaching an ABCL or
AOCL whenever the DWL is not LIT.
DRIVERS WHITE LIGHT (DWL) A SIGNAL that is displayed to a train driver approaching an ABCL or
AOCL to indicate that the LEVEL CROSSING protection system
has activated.
DROP SHUNT The maximum value of resistance which, when placed across the
rails at the relay end of a TRACK CIRCUIT, will cause the RELAY
to de-energise (that is to just break the FRONT CONTACTs).
DRY LOOP A circuit, with no flow of direct current.
DTMF Dual Tone Multi Frequency A term for push button telephone
dialling method or Touch-tone (an AT&T trademark), by using
two out of five tones.
DUMMY A slang word for a ground shunting signal (mechanical or colour
light)
DWL Abbreviation for DRIVERS WHITE LIGHT.
DYING PIG A term used to describe an ANNUNCIATOR that sounds on the
operation of a TRACK CIRCUIT or TREADLE on the approach to
a signal box or a signalman operated level crossing and gradually
reduces as a capacitor discharges through the ANNUNCIATOR.
ECONOMISER Generally a LEVER LOCK contact internally wired in series with the
coil such that the lock is not energised when the lever is not in the
full travel position.
ELECTRIC KEY TOKEN (EKT OR A signalling system on SINGLE LINES controlled by the use of
ET) BLOCK physical TOKENS, only one of which can be released from the
instruments at any one time.
ELECTRIC KEY TOKEN (EKT OR The equipment in a BLOCK POST or SIGNAL BOX for the operation
ET) INSTRUMENT of ELECTRIC KEY TOKEN BLOCK.

TERM DEFINITION
ELN Abbreviation for Emergency Lock Plunger, an EMERGENCY
RELEASE device that allows the operation of a FACING POINT
LOCK lever during a TRACK CIRCUIT failure.
EMERGENCY RELEASE A device, usually sealed, to permit the operation of a signalling
function in case of emergency or failure, which will bypass the
failed electrical interlocking.
EMERGENCY SPEED A TEMPORARY SPEED RESTRICTION which has not been
RESTRICTION published in any railway operating notice, or which is more
restrictive than shown, or which applies at a time not shown.
ENGINEERING TOKEN A type of TOKEN that gives engineering staff POSSESSION of a
single line. Often used where the single line is not controlled by
any form of physical token.
ENTRANCE-EXIT (NX) A ROUTE setting system on a geographical panel which is controlled
by the operation of buttons or switches at the entrance and exit of
the ROUTE.
EUROPEAN RAILWAY TRAFFIC An automatic train protection system (ATP) to replace the existing
MANAGEMENT SYSTEM national ATP-systems
(ERTMS)
EXIT SIGNAL The SIGNAL (or BUFFER STOP, STOP BOARD) at the end of a
ROUTE.
FACING (DIRECTION) The direction of traffic over POINTS where the train meets the TOE
of the SWITCH RAIL first (diverging junction - the driver is faced
with a choice of route).
FACING POINT LOC A FACING POINT LOCK mechanically operated by the same lever
(ECONOMICAL) that operates the POINTS.
FACING POINT LOCK (FPL) A MECHANICAL means of physically locking POINTS so they
cannot be moved, may be provided independently or incorporated
in a POINT MACHINE.
FACING POINT LOCK BAR A lifting bar to prevent the unlocking of FACING POINTS while a
train is passing over them. Also known as a LOCKING BAR.
FACING POINTS POINTS capable of carrying RUNNING MOVEMENTS in a FACING
DIRECTION.
FAIL-SAFE A design philosophy which results in any expected failure
maintaining or placing the equipment in its most restrictive state.
FALSE CLEAR (TRACK CIRCUIT) A condition where a TRACK CIRCUIT indicates the line is
unoccupied when it is OCCUPIED by a train. This is a WRONG
SIDE FAILURE.
FEATHER A slang term for a white light junction indicator.
FIBRE-OPTIC INDICATOR An indicator that uses optical fibres to provide the required
illuminated indication.

TERM DEFINITION
FIBRE-OPTIC SIGNAL A COLOUR LIGHT SIGNAL that uses optical fibres to provide the
required ASPECTs. Other uses include BANNER and POSITION
LIGHT SIGNALs. See also SEARCHLIGHT SIGNAL.
FIRST CAUTION The SIGNAL ASPECT which gives the driver the first indication of a
need to stop. Can also be known as PRELIMINARY CAUTION.
FIRST WHEEL REPLACEMENT A control applied to a SIGNAL which replaces it to its most restrictive
ASPECT when the first wheel of the train occupies a TRACK
CIRCUIT or other TRAIN DETECTION device immediately
BEYOND the signal.
FIXED DISTANT SIGNAL A DISTANT SIGNAL that is only capable of displaying a CAUTION.
Can be either a YELLOW ASPECT or a MECHANICAL DISTANT
ARM.
FLANK PROTECTION Protection from overrunning movements approaching on converging
tracks, usually by additional SIGNAL and/or point
INTERLOCKING.
FLASHING DOUBLE YELLOW A COLOUR LIGHT SIGNAL ASPECT which informs the driver that
(ASPECT) the next MAIN SIGNAL is displaying a FLASHING SINGLE
YELLOW.
FLASHING SINGLE YELOOW A COLOUR LIGHT SIGNAL ASPECT which informs the driver that
(ASPECT) the next MAIN SIGNAL is displaying a SINGLE YELLOW with a
JUNCTION INDICATOR set for a DIVERGING ROUTE.
FOG SIGNAL See DETONATOR.
FOOTPATH LEVEL CROSSING A LEVEL CROSSING that is designated only for pedestrians.
(FP)
FOULING BAR A mechanically operated form of TRAIN DETECTION activated by
the flange of a wheel (frequently confused with a FACING POINT
LOCK BAR).
FOULING POINT The place where a vehicle standing on a converging line would come
into contact with a vehicle on another line.
FOUR ASPECT SIGNALLING A system of colour light signalling which provides RED, YELLOW,
DOUBLE YELLOW and GREEN ASPECTs in a manner which
normally provides a FIRST CAUTION at least two SIGNALs
before a Signal at red.
FREE WIRED INTERLOCKING A RELAY based interlocking that comprises of individually wired
relays, and other equipment, rather than pre-wired sets.
Common systems in use conform to standardised systems such
as examples are BR850 or E10K
FREQUENCY DIVISION A data transmission system that uses unique frequencies to separate
MULTIPLEX (FDM) channels over a single pair of conductors. Normally used for
VITAL INTERLOCKING functions.
FROG Another term for CROSSING.

TERM DEFINITION
FULL BARRIERS Single or double BARRIERs, provided at CONTROLLED LEVEL
CROSSINGs, which extend across the whole width of a road.
BARRIER SKIRTS may be provided.
FULL OVERLAP An OVERLAP of at least 440 yards for semaphore signals or 200
yards (180 metres) where both the HOME and DISTANT are
COLOUR LIGHT SIGNALs. Distances vary dependant on line
speed.
GANTRY A structure spanning one or more tracks and having two or more
points of support.
GATE (LEVEL CROSING) A device pivoted at the side of the road (or FOOTPATH or
BRIDLEWAY) which is closed when required to enable trains to
pass. The gate may close across the railway when the road is
open.
GATE BOX A control point provided for the supervision of one or more LEVEL
CROSSINGs which are not controlled directly by a SIGNAL BOX.
A Gate Box is not a BLOCK POST.
GATE STOP (RAIL) A device that holds the GATE locked across the railway. Part of this
device may be fixed.
GATE STOP (ROAD) A device that is normally flush with the road surface and rises as the
gate approaches to hold the GATE locked across the roadway.
GATE STOP LEVER Lever that, when placed from REVERSE to the backlock (B)
position, lowers the rail stops and prepares the rising of the road
stops. When placed fully NORMAL, it locks the road stops in the
raised position. Interlocked with the signalling.
GATE WHEEL A wheel provided in a SIGNAL BOX or GATE BOX with which the
SIGNALMAN or CROSSING KEEPER operates the GATES.
GEOGRAPHICAL An INTERLOCKING where standard pre-assembled modules are
INTERLOCKING provided for each signalling function which are arranged and
electrically interconnected in a geographical manner.
GREEN (ASPECT) Displayed by a COLOUR LIGHT SIGNAL, indicates to the driver that
the next SIGNAL is showing a PROCEED ASPECT.
GROUND FRAME A normally unmanned control point containing levers (and/or other
equipment) to permit the local operation of POINTS and/or
SIGNALs. The local operation is usually dependent upon a
release being given from a SIGNAL BOX or by a key on a TRAIN
STAFF or by a TOKEN. See also SHUNT FRAME.
GROUND POSITION LIGHT A POSITION LIGHT SIGNAL mounted at ground level.
SIGNAL (GPL)
GROUND SHUNT SIGNAL A SHUNTING SIGNAL at ground level.
GROUND SWITCH PANEL A GROUND FRAME which only uses switches or buttons as
operating devices.

TERM DEFINITION
HALF-BARRIER A BARRIER for closing the entrance to a LEVEL CROSSING to the
oncoming road traffic, whilst maintaining the exit from the
crossing open.
HAND POINTS POINTS work manually by an independent lever adjacent to the
points that are not interlocked with signals.
HANDSIGNAL An indication given to a driver, or other personnel as required, to be
used in the absence of a SIGNAL.
HEADWAY The shortest distance or time interval between two following trains,
so that the second train can run at normal operating speed
without being restricted by the SIGNAL ASPECTs.
HEEL The end of the SWITCH RAIL which is fixed in position.
HER MAJESTYS RAILWAY A branch of the Office of the Rail Regulator (ORR) which accepts
INSPECTORATE (HMRI) Safety Cases, and enforces health and safety.
HOME NORMAL CONTROL (HNC) The HOME SIGNAL LEVER is proved NORMAL (and the
SEMAPHORE SIGNAL arm proved ON, where repeated) before
the SIGNALMAN can give LINE CLEAR to the BLOCK POST in
rear. This prevents the signalman giving permission for a train to
approach when the home signal is not on. Also known as home
normal contact or home normal proving. See also INTERLINKING
and SEQUENTIAL LOCKING.
HOME SIGNAL In BLOCK SIGNALLING, the first STOP SIGNAL on the APPROACH
TO, and worked from, a SIGNAL BOX.
HOT LINE A telephony feature that provides a direct connection through a
public or private automatic telephone system, initiated by lifting
the handset, to a pre-determined destination without dialling.
HOT STRIP A segment in a COLOUR LIGHT SIGNAL lens which deflects a
portion of the beam for short range viewing by the driver stopped
at the signal.
HSE Health & Safety Executive (railway duties now with the ORR)
HUDDERSFIELD CONTROL INTERLOCKING between a SIGNAL and a CALLING-ON ROUTE
leading up to the signal.
HYDRO-PNUMATIC POINTS A particular type of TRAIN OPERATED POINTS.
IDENTIFICATION LABEL Any sign or label fixed to the outside of a telephone, to help locate
the telephone and indicate its function.
IEE Institution of Electrical Engineers (Now the IET).
IFS Abbreviated term for INDIVIDUAL FUNCTION SWITCH.
ILLUMINATED DIAGRAM A SIGNAL BOX DIAGRAM on which TRACK CIRCUIT and other
indications are provided by means of lights on a representation of
the track layout.

TERM DEFINITION
IN ADVANCE OF In relation to a location or equipment on or alongside the track,
positioned such that a train reaches it after passing another
defined location (see also BEYOND).

Direction of Travel
------------------------------------X----------------------------------
In rear of Point X In advance of Point X
IN REAR OF In relation to a location or equipment on or alongside the track,
positioned such that a train reaches it before passing another
defined location (see also APPROACH TO).

Direction of Travel
------------------------------------X----------------------------------
In rear of Point X In advance of Point X
INDICATION LOCKING A Western Region term for CHECK LOCKING, often applied to
levers controlling POWER OPERATED POINTS.
INDICATOR (SIGNAL BOX) A visual device which displays the position or condition of an item of
signalling equipment.
INDIVIDUAL FUNCTION SWTICH A non-route setting panel where each switch or button performs a
(IFS) separate function.
INFORMATION LABEL A label usually fitted to an internal surface of a telephone housing,
providing essential information to the user.
INNER HOME SIGNAL A term used on some railways for a second HOME SIGNAL at a
SIGNAL BOX, particularly where the first home signal does not
protect a set of POINTS (e.g. Great Western Railway and
BR(WR)).
INSELLS LOCK A means of holding a SIGNAL in advance of a diverging junction at
red where there is a risk of misreading or READING THROUGH.
INSULATED BLOCK JOINT An alternative term for INSULATED RAIL JOINT.
INSULATED RAIL JOINT (IRJ) A joint between two rail sections with insulation.
INTERLINKING SIGNAL BOX controls to enforce electrical SEQUENTIAL LOCKING
by proving the HOME and DISTANT SIGNALs ON and the
BERTH TRACK CIRCUIT CLEAR before allowing LINE CLEAR
and the ACCEPTANCE of a train.
INTERLOCKING A general term applied to the controlling of the setting and release of
SIGNALs and POINTS to prevent unsafe conditions arising, and
the equipment which performs this function. Can be applied to
mechanical or electrical equipment
INTERLOCKING FRAME An alternative term for LEVER FRAME.

TERM DEFINITION
INTERMEDIATE BLOCK (HOME) A SIGNAL controlling the exit from an INTERMEDIATE BLOCK
SIGNAL SECTION.
INTERMEDIATE BLOCK A train detected portion of line between the SECTION SIGNAL and
SECTION the INTERMEDIATE BLOCK SIGNAL, both of which are operated
from the same SIGNAL BOX or BLOCK POST. It is situated
between adjacent SIGNAL BOXes or BLOCK POSTs to improve
HEADWAY.
INTERMEDIATE TOKEN A mid section TOKEN INSTRUMENT, usually located at a GROUND
INSTRUMENT FRAME and associated with shutting-in facilities. Does not
include BLOCK SECTION release controls on the section signals.
IRJ PLAN A Western Region term for BONDING PLAN.
IS (ARE) REQUIRED Used to indicate choices where firmer guidance might be indicated.
ISOLATE To take electrical equipment out of use.
JOINTLESS TRACK CIRCUIT A TRACK CIRCUIT which does not require INSULATED RAIL
(JTC) JOINTS at its extremities.
JUMPER An interconnection cable to provide electrical continuity. Normally
associated with track circuits.
JUNCTION INDICATOR An INDICATOR provided at a JUNCTION SIGNAL to inform the
driver that a junction is set for a diverging route.
JUNCTION SIGNAL Any SIGNAL that has more than one running ROUTE and is capable
of displaying an indication of the route.
KEY TOKEN A type of TOKEN used for ELECTRIC TOKEN BLOCK and is
normally restrained within a TOKEN INSTRUMENT.
KING LEVER A lever which, when operated, releases the INTERLOCKING
between other levers. It is usually provided for the purpose of
switching out a SIGNAL BOX.
KIOSK A London Underground term for LOCATION case
LADDER JUNCTION A sequence of POINTS on a multi-track section of railway arranged
as a series of CROSSOVERs.
LAMP PROVING A system that ensures the required lamp is ALIGHT by measuring
the current drawn by an electric lamp or by detecting the heat
rising from an oil lamp.
LAST WHEEL REPLACEMENT A control applied to a SIGNAL which replaces it to its most restrictive
ASPECT when the last wheel of the train clears the BERTH
TRACK CIRCUIT of the signal after it occupies the TRACK
CIRCUIT or other TRAIN DETECTION device immediately
BEYOND the signal.
LATCHED A term used in connection with relays where the relay will remain in
the last operated position when no supply is present
LED SIGNAL A COLOUR LIGHT SIGNAL that uses Light Emitting Diode
technology in place of incandescent lamps and coloured filters.
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TERM DEFINITION
LEFT-HAND RAIL The left-hand rail of the track to which a SIGNAL (or equipment)
relates, as viewed from a train approaching the signal.
LEFT HAND SWITCH CLOSED A term to describe the position of a point.
(LHSC)
LEVEL CROSSING (LC) An intersection at the same elevation of a road and one or more rail
tracks.
LEVEL CROSSING GATE See GATE (LEVEL CROSSING).
LEVEL CROSSING ORDER A legal document, made by the Secretary of State, which details the
controls to be provided and the circumstances in which a LEVEL
CROSSING may be brought into use.
LEVEL CROSSING WARNING Alternative name for ADVANCED WARNING BOARD.
SIGN
LEVER A mechanical device for operation signalling equipment either
mechanically or electrically.
LEVER BANDS Contacts housed in a CIRCUIT CONTROLLER that is associated
with a LEVER.
LEVER COLLAR A device which, when applied, is a reminder that a LEVER in a
LEVER FRAME must not be operated or only operated under
certain conditions. See REMINDER APPLIANCE.
LEVER FRAME A frame in which LEVERs working SIGNALs, POINTS and other
equipment in the area are mounted together and usually
INTERLOCKED.
LEVER LEAD A Western Region term for a LEVER PLATE.
LEVER LOCK An electro-mechanical mechanism fitted to hold (and release) the
LEVER in a predetermined position.
LEVER PLATE An identification plate fixed to a LEVER (or sometimes behind the
LEVER), describing the lever function together with the order of
pulling details. Also known as PULL PLATE, LEVER LEAD, or
Lever Badge.
LEVER WORKED TO MAINTAIN A spare LEVER, formally controlling a signalling function but
LOCKING remaining connected to the MECHANICAL LOCKING, that is
required to be worked to allow other LEVERs to be operated.
Sometimes shown as Spare Worked to Maintain Locking.
LIME STREET CONTROLS The ability to allow a PERMISSIVE move to take place into an
occupied platform by having suitably measured the length of the
second train and the space available in the platform. The lengths
of SIGNAL BERTH TRACK CIRCUIT and platform TRACK
CIRCUIT are designed to enable these controls to be performed.
LIMIT OF SHUNT INDICATOR A sign to terminate a SHUNTING MOVEMENT along a line in the
(LOS) WRONG DIRECTION. It is to be treated as a SHUNTING
SIGNAL which is fixed at stop.

TERM DEFINITION
LIMIT OF SHUNTING A sign to indicate the limit of certain SHUNTING MOVEMENTs. It
MOVEMENTS SIGN may be passed for other movements to which it does not apply.
LINE BLOCKED (LB) The normal state of a BLOCK SECTION when permission has not
been given for a train to enter it.
LINE CAPACITY For a given section of line, the practical maximum number of trains
per hour permitted by the signalling system.
LINE CLEAR (LC) The state of the BLOCK SECTION after a train has been accepted
but before it has entered the section.
LINE SPEED The permissible speed of trains on a route of railway. Also known as
PERMISSIBLE SPEED.
LINESIDE TELEPHONE Any fixed telephone installed on or about the railway and required for
day-to-day running of the railway.
LIT An alternative term for ALIGHT.
LOADING/UNLOADING Indicators that relay movement instructions to drivers when
INDICATORS controlling trains in sidings. Also known as Toton or CREEP
SIGNALS.
LOCAL CONTROL UNIT (LCU) Equipment provided at an AUTOMATIC LEVEL CROSSING to
enable it to be manually operated locally. A local control unit may
also be provided to enable other equipment to be operated
locally.
LOCATION (CASES) One or more signalling lineside apparatus housings at a particular
site.
LOCK STRETCHER A STRETCHER bar that is secured by a FACING POINT LOCK.
LOCKED The state of any signalling function or item of equipment when it is
conditionally or unconditionally prevented from changing state or
position by other parts of the signalling system.
LOCKING BAR An alternative name for FACING POINT LOCK BAR.
LOCKING CHART A pictorial representation of the INTERLOCKING elements required
for MECHANICAL LOCKING, sometimes referred to as Dog
Chart
LOCKING LEVEL The INTERLOCKING level where controls between signalling
functions are required to be satisfied before a ROUTE can be set.
LOCKING SKETCH A Western Region term for SIGNALLING PLAN
LONG SECTION TOKEN A TOKEN section covering two or more SINGLE LINE sections when
the SIGNAL BOXes or BLOCK POSTs are switched out. May
also apply to TABLET or TRAIN STAFF sections.
LONGITUDINAL POSITION The position of a SIGNAL (or other piece of equipment) along the
track, usually specified in terms of miles and chains (or yards), or
kilometres from a specified datum point.

TERM DEFINITION
LOWER QUADRANT A term applied to a SEMAPHORE SIGNAL whose CLEAR position is
designated by the arm below the horizontal.
MAGNETO Magneto signalling; A simple low frequency ac ringing supply
originally 16 2/3 Hz but latterly 25Hz at about 75 volts.
Magneto Telephone; A type of local battery telephone fitted with an
internal generator that will generate its own ringing supply.
Magneto Circuit; A dry loop speech circuit with magneto signalling.
MAIN (ROUTE CLASS) A ROUTE from one MAIN SIGNAL to the next that allows running
moves. It requires the section and OVERLAP to be CLEAR.
MAIN ARM An arm of a SEMAPHORE MAIN SIGNAL controlling a RUNNING
MOVEMENT.
MAIN ASPECT The RED, YELLOW, DOUBLE YELLOW or GREEN ASPECT of a
COLOUR LIGHT SIGNAL.
MAIN SIGNAL A COLOUR LIGHT SIGNAL capable of displaying a MAIN ASPECT
or a SEMAPHORE DISTANT or STOP SIGNAL.
MAINTAINED LOCKING An alternative term for ROUTE LOCKING.
MANNED CONTROLLED A CONTROLLED LEVEL CROSSING with FULL BARRIERS
BARRIERS (MCB) operated by a SIGNAL BOX or GATE BOX.
MANNED LEVEL CROSSING A LEVEL CROSSING that is operated or supervised by a member of
the railway staff.
MAY Used where guidance suggests optional choice.
MECHANICAL Operated directly without any form of power assistance.
MECHANICAL DISTANT ARM Normally a 4 -5 arm that has a fishtail at its end and is coloured
yellow with a black chevron
MECHANICAL LOCKING A method of INTERLOCKING where the components are movable
metal pieces which physically lock and prevent the movement of
one lever against another.
MINIATURE ARM An arm of a SEMAPHORE SIGNAL which is smaller than a MAIN
ARM but does not control a RUNNING MOVEMENT.
MINIATURE LEVER FRAME A LEVER FRAME of miniature LEVERs for the control of power
operated signalling.
MINIATURE RED/GREEN LIGHTS An alternative term for MINIATURE STOP LIGHTS.
(R/G)
MINIATURE STOP LIGHTS (MSL) An AUTOMATIC LEVEL CROSSING equipped with miniature
red/green warning lights operated by approaching trains.
MINIATURE WARNING LIGHTS An obsolete term for MINIATURE STOP LIGHTS.
(MWL)

TERM DEFINITION
MINITURE ALPHANUMERIC An alphanumeric display presented to the driver to indicate the route
ROUTE INDICATOR (MARI) set. It is for short range use. Also known as STENCIL
INDICATOR.
MOTOR OPERATED Power operated by a motor or similar device connected to the signal
arm (applicable to SEMAPHORE SIGNALS). Can also apply to
POINTS and some other equipment.
MULTI-LAMP ROUTE INDICATOR A large alphanumeric route indicator (normally used in conjunction
with a MAIN SIGNAL, or sometimes a SEMAPHORE SIGNAL),
where the indication letters and numbers are formed by a
combination of lamps. See also THEATRE INDICATOR.
MULTIPLE ASPECT SIGNALLING A system of signalling using COLOUR LIGHT SIGNALS, TRACK
CIRCUITS BLOCK and usually ROUTE SETTING.
MUST Used only where there is a legal or statutory requirement to the
measures being described.
NEUTRAL A term used in connection with relays where the polarity of the
supply does not affect the relay operation
NO BLOCK A system of operating rail traffic where the condition of the BLOCK
SECTION is not monitored.
NO SIGNALMAN KEY TOKEN A system of working trains on a SINGLE LINE using an ELECTRIC
(NSKT OR NST) TOKEN, where the TOKEN INSTRUMENTs at one or both ends
of the section may be operated by the train crew. The movement
of all trains into the SECTION is monitored by a SIGNALMAN,
who gives a release for each TOKEN issued. May also apply to
TABLET or TRAIN STAFF sections.
NO SIGNALMAN TOKEN WITH A system of working trains on a SINGLE LINE with the driver or other
REMOTE CROSSING LOOPS authorised person responsible for operating the TOKEN
(NSTR) INSTRUMENTs at one or more locations remote from the
SIGNAL BOX, after obtaining verbal permission from the
SIGNALMAN.
NON-BLOCK SIGNAL A SIGNAL provided within a BLOCK SECTION that does not have
block section controls. Normally provided for LEVEL CROSSING
protection.
NON-VITAL A term for a description applied to those parts of the signalling
system whose failure or non-availability does not directly
endanger rail traffic or reduce the integrity of the signalling
system.
NORMAL (ASPECT) The most restrictive ASPECT of a CONTROLLED SIGNAL .
NORMAL (LEVER) Position of a LEVER in the LEVER FRAME when the lever has not
been pulled (i.e. back in the frame).
NORMAL (POINTS) Position of POINTS when the lever to which they are connected is
NORMAL (LEVER).

TERM DEFINITION
NSTR An abbreviation for NO SIGNALMAN TOKEN WITH REMOTE
CROSSING LOOPS.
NX Abbreviated term for ENTRANCE-EXIT
OBSCURATION The obscuring or hiding of a SIGNAL or part of a SIGNAL which
impairs sighting.
OCCUPATION An alternative term for POSSESSION.
OCCUPATION LEVEL CROSSING A private LEVEL CROSSING which gives access between premises
and a public highway or between land/premises under common
occupation but divided by the railway line.
OCCUPIED (OCC) A section of track having any part of a train on it.
OCS An abbreviated term for ONE CONTROL SWITCH.
OFF (ASPECT) A PROCEED ASPECT in a COLOUR LIGHT SIGNAL, or the arm of
a SEMAPHORE SIGNAL or DISC SIGNAL inclined at 35 degrees
or more.
OFF INDICATOR An INDICATOR that displays the word OFF, to indicate that the
SIGNAL ahead is CLEARed prior to starting the train, usually
associated with a PLATFORM STARTING SIGNAL.
OMNIBUS TELEPHONE A type of telephone designed to be used in parallel with others along
the length of a common line and using various means of selection
and ringing. Often there is no provision for privacy between
telephones.
Alternatively a local battery powered telephone suitable for operation
in parallel across a common line with single polarity or multi
button polarised battery coded ringing.
ON (ASPECT) A RED ASPECT in a COLOUR LIGHT STOP SIGNAL, or YELLOW
ASPECT in a COLOUR LIGHT DISTANT SIGNAL, or the arm of
a SEMAPHORE SIGNAL or a DISC SIGNAL in the horizontal
position.
ONE ACCEPTANCE BLOCK In ABSOLUTE BLOCK, prevents the SIGNALMAN from accepting a
second train without the first having occupied and cleared the
HOME SIGNAL BERTH TRACK CIRCUIT.
ONE CONTROL SWITCH (OCS) A type of ROUTE SETTING control panel having one switch (or
other device) to control each ROUTE.
ONE PULL (RELEASE) Allows the SIGNALMAN to operate the SECTION SIGNAL only once
for each LINE CLEAR.
ONE TRAIN (RELEASE) Allows the SIGNALMAN to operate the SECTION SIGNAL for only
one train for each LINE CLEAR.
ONE TRAIN STAFF INSTRUMENT A designated container (or TOKEN INSTRUMENT etc.) for the safe
storage of a single TRAIN STAFF or TOKEN for ONE TRAIN
WORKING.

TERM DEFINITION
ONE TRAIN WORKING (OTW) Method of signalling a SINGLE LINE, with or without a TRAIN
STAFF, where only one train is permitted at a time.
With a train staff [OT(S)]
Without a train staff [OT]
OPEN CROSSING (OC) A LEVEL CROSSING that has no BARRIERS, gates or road traffic
light signals and which is protected only by signs.
OPERATIONAL A telephone used for
TELECOMMUNICATIONS (a) Authorising the movement of trains.
(b) Safety- related communications purposes in the direct
operation of the railway.
ORR Office of Rail Regulation
OSGR Ordnance Survey Grid Reference
OT Abbreviated term for ONE TRAIN WORKING without a TRAIN
STAFF.
OT(S) Abbreviated term for ONE TRAIN WORKING with a TRAIN STAFF.
OTW Abbreviated term for ONE TRAIN WORKING.
OUT OF USE (OOU) Non-operational equipment that is still connected to the signalling
system.
OUTER HOME SIGNAL A term used on some railways for the first HOME SIGNAL at a
SIGNAL BOX, particularly where a second signal exists before
the first set of POINTS (e.g. London and North Western Railway).
OVERLAP (OL) The section of line BEYOND a STOP SIGNAL that must be clear and
any points locked before and during a signalled move up to the
STOP SIGNAL.
OVERLAY TRACK CIRCUIT A TRACK CIRCUIT which operates within and additionally to,
another TRACK CIRCUIT. Normally used for detection of a train
at a specific position.
OVERRIDE A facility provided at some remote INTERLOCKINGs for use during
failure of the remote control equipment. It enables all SIGNALs to
be replaced to DANGER or nominated ROUTEs to be set for
automatic working. Limited selective routing at junctions is
sometimes provided. Also known as THROUGH ROUTES.
PARALLEL BONDING A method of bonding rail section where track circuit integrity is
achieved by the use of parallel paths. See also YELLOW BOND.
PARALLEL SIGNALS Signals applying to parallel lines signalled in the same direction,
which have been placed in the same LONGITUDINAL
POSITION.
PASSENGER LINE A line signalled to the standard required for trains conveying
passengers.
PATROLMAN A person who patrols/inspects a section of line.
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TERM DEFINITION
PATROLMANS LOCKOUT A line side mounted device that allows a PATROLMAN, with the
DEVICE (PLOD) permission of the SIGNALMAN, to prevent the signalled
movement of trains, for example, in one direction only on a BI-
DIRECTIONAL LINE.
PERMANENT SPEED The normal speed restriction for the operation of trains over a section
RESTRICTION (PSR) of line.
PERMISSIBLE SPEED An alternative term form LINE SPEED.
PERMISSIVE BLOCK A form of PERMISSIVE WORKING through a BLOCK SECTION.
PERMISSIVE WORKING A method of working that allows RUNNING MOVEMENTS into an
OCCUPIED section of track on designated lines.
PETS Public Emergency Telephone System A telephone connection
system used principally at AHB crossings to provide a secure
telephone system with monitoring of the telephones for integrity.
As the system is designed for a maximum of 4 telephones at the
distant end it may be used to serve a group of telephones,
perhaps at adjacent crossings, over one line pair back to the
signal box.
PHANTOM ASPECT Light emitted from a SIGNAL lens assembly that has originated from
an external source (usually the sun) and has been internally
reflected within the SIGNAL HEAD in such a way that the lens
assembly gives the appearance of being lit.
PHANTOM OVERLAP (POL) A calculated OVERLAP that does not correspond to a physical
boundary between train detection sections. It is used where the
overlap distance falls short of a set of POINTS and those points
are not locked by the overlap.
PHANTOM RESTRICTED An OVERLAP that contains the special features of a PHANTOM
OVERLAP (POL) OVERLAP and a RESTRICTED OVERLAP.
PILOTMAN A person appointed to authorise the passage of trains over a
SINGLE LINE during failure of equipment, during repairs or due
to an obstruction.
PIVOT LIGHT A light that is common to both ON and OFF ASPECTS of a
POSITION LIGHT SIGNAL.

TERM DEFINITION
PLATFORM STARTING SIGNAL A STOP SIGNAL at, or near, the departure end of a station platform.
Normally defined by;
the longest passenger (or empty coaching stock) train
authorised to use the platform would, if stopped at the
SIGNAL, still have a portion of the passenger accommodation
alongside the platform, or
if the leading end of the train passes over the AWS equipment
(where fitted) associated with the SIGNAL before it is
despatched from the platform.
(Note; in BLOCK SIGNALLING, this signal may also be a HOME
SIGNAL.
PLUNGER A button that is depressed to activate signalling equipment.
POINT DETECTOR A device for proving that POINTS are correctly SET before a
SIGNAL can be CLEARed to authorise the passage of a train
over the points.
POINT END One pair of SWITCH RAILS in a set of POINTS.
POINT MACHINE The equipment for the powered operation of a set of POINTS.
POINTS The items of permanent way which may be aligned to one of two
positions, NORMAL or REVERSE, according to the direction of
train movement required.
POLAR A term used in connection with relays where the polarity of the
supply does affect the relay operation
POSITION LIGHT GROUND An alternative term for GROUND POSITION LIGHT (GPL).
SIGNAL (PLGS)
POSITION LIGHT JUNCTION An INDICATOR which displays the ROUTE at a SIGNAL by means
INDICATOR (PLJI) of a line of white lights.
POSITION LIGHT SIGNAL A SIGNAL, other than a MAIN SIGNAL, that displays its ASPECT by
the position and colour of its lights.
POSSESSION (ABSOLUTE, OF A The complete stoppage of trains on a particular RUNNING LINE for
LINE) engineering purposes. Also referred to as an ABSOLUTE
POSSESSION.
POSSESSION (OF SIGNALLING The disconnection or restriction of use of signalling equipment
EQUIPMENT) agreed between maintenance and operations staff to enable work
to be carried out on the equipment.
POWER FRAME A LEVER FRAME controlling only power operated equipment. See
also MINIATURE LEVER FRAME.
POWER OPERATED POINTS POINTS operated by means other than MECHANICAL.
PRELIMINARY CAUTION An ASPECT displayed to the driver to indicate that the next signal is
at CAUTION (aspect displayed is normally DOUBLE YELLOW).

TERM DEFINITION
PRE-SET SHUNT Where facing shunting SIGNALs exist in the line of route on a route
setting panel these will be cleared (generally automatically)
before the main (presetting) signal clears.
PREVENT SHUNT The prevent shunt of a TRACK CIRCUIT is the value of resistance
connected across the rails at which the track circuit RELAY
energises (that is, it just makes its front contacts).
PROCEED ASPECT Any SIGNAL ASPECT which permits the driver to pass the signal.
PROPELLING MOVEMENT A movement involving the pushing of a vehicle or vehicles by a
traction unit.
PROTECTED WRONG SIDE A WRONG SIDE FAILURE where another part of the signalling
FAILURE system provides an acceptable level of protection.
PROTECTING SIGNAL A SIGNAL that protects a train from CONFLICTING MOVEMENTS
and/or obstructions.
PROVED Evidence provided by electrical or other means that a function is in
its correct state.
PULL PLATE An alternative term for LEVER PLATE.
RA An abbreviated term for RIGHT AWAY INDICATOR.
RAIL CIRCUIT TRAIN DETECTION equipment using the rails in an electric circuit,
which detects the presence of a train (as opposed to its absence).
See TRACK CIRCUIT, OVERLAY TRACK CIRCUIT.
RAYNES PARK CONTROL The name given to ensure that APPROACH CONTROL is effective.
The RELAY (or equivalent) that applies the approach control is
proved not operated in the SIGNAL in REAR.
READING THROUGH The ability to observe one or more SIGNAL(s) BEYOND the signal
which the driver is approaching so as to mislead or confuse the
driver.
READY TO START INDICATOR An alternative term for RIGHT AWAY INDICATOR.
READY TO START PLUNGER An alternative term for RIGHT AWAY PLUNGER.
RECIPROCAL LOCKING The provision of INTERLOCKING between functions to ensure that
conditions cannot be broken down, e.g. if 1 locks 2 then 2 must
lock 1 (see also CONVERSE LOCKING).
RED (ASPECT) Displayed by a COLOUR LIGHT SIGNAL, indicates to the driver to
stop at that signal.
RED/GREEN LIGHTS (R/G) Alternative term for MINIATURE STOP LIGHTS.
REDUCED OVERALP An OVERLAP that is shorter than the minimum permitted length of a
FULL OVERLAP, where the permitted approach speed is below a
specified level which still allows an unrestricted approach to a
SIGNAL at danger.
RELAY An electro-mechanical switching device used in many types of
signalling systems.
IRSE 2011
Uncontrolled when Printed
Institution of Railway Signal Engineers Minor Railways Section Guideline on
Ref: Glossary Issue 1.0 Glossary of Signalling and Telecommunications Terminology
January 2011 Page 29 of 39

TERM DEFINITION
RELAY INTERLOCKING A method of INTERLOCKING where the safely logic is implemented
by RELAYs.
REMINDER APPLIANCE A device or control which is used to remind the SIGNALMAN that a
button, switch or lever should not be operated or should be
operated only under certain conditions. See LEVER COLLAR.
REPEATER An alternative term for an INDICATOR (SIGNAL BOX).
REPEATER SIGNAL A SIGNAL (not in itself a STOP SIGNAL) capable of displaying a
CAUTIONARY ASPECT, that informs the driver about the state of
the next stop signal ahead.
RESTRICTED OVERLAP (ROL) An OVERLAP that is shorter than the minimum permitted length of a
FULL OVERLAP, which is available only when the preceding
SIGNAL is subject to APPROACH CONTROL by selection of a
WARNING ROUTE or signal.
REVERSE (FUNCTION) Position of a LEVER (or switch) when it is pulled fully in the LEVER
FRAME (or operated).
REVERSE (POINTS) The opposite position to NORMAL (POINTS).
RGS Railway Group Standard published by RSSB
RIGHT AWAY INDICATOR An INDICATOR that displays RA or R to inform the driver that the
train may start from the platform.
RIGHT AWAY PLUNGER The PLUNGER or other device used to initiate the operation of a
RIGHT AWAY INDICATOR.
RIGHT HAND SWITCH CLOSED A term used to describe the position of a point.
(RHSC)
RIGHT SIDE FAILURE A failure which does not result in the protection provided by the
signalling system being reduced. See FAIL-SAFE
ROAD TRAFFIC SIGNAL A mandatory stop signal for road traffic comprising of an amber light
and two flashing red lights.
ROGS REGULATIONS Railways and Other Guided Transport Systems (Safety) Regulations
2006.
ROUTE The path along a section of track from one SIGNAL to another
ROUTE INDICATOR An INDICATOR associated with a SIGNAL which indicates which
ROUTE is set, where more than one is available
ROUTE LOCKING A form of INTERLOCKING which maintains the locking associated
with a ROUTE in use until after the train has passed the
equipment being LOCKED (eg, POINTS).
ROUTE RELAY INTERLOCKING A RELAY based INTERLOCKING system controlled from a ROUTE
(RRI) SETTING PANEL.
ROUTE RELEASING The release of ROUTE LOCKING

TERM DEFINITION
ROUTE SETTING A system in which all POINTS in a ROUTE are set to the required
positions, and the SIGNAL at the entrance to the route
CLEARE,D by the operation of one or two control functions.
ROUTE SETTING PANEL A panel which embodies the controls and displays the condition of all
associated signalling equipment for a ROUTE in a specific
geographic location. See also ROUTE SETTING.
RSD Railway Safety Directorate (formally HMRI), now a function within
ORR.
RSPG Railway Safety Principles & Guidance by HSE (now ORR) most of
these documents are now obsolete and some have been
replaced by the ORR Railway Safety Publications.
RSSB Rail Safety and Standards Board
RUN THROUGH A movement through TRAILING POINTS SET in the wrong direction.
RUNNING LINE A line that runs between two distinct locations usually, but not
always, under the control of MAIN SIGNALs.
RUNNING MOVEMENT A train movement on a RUNNING LINE, under the control of a MAIN
SIGNAL.
RUNNING SIGNAL An alternative term for MAIN SIGNAL.
RURAL BARRIERS A type of barrier equipment that is designed to be operated locally by
the user; typically provided at a USER WORKED CROSSING.
SAFETY CRITICAL Directly influencing safety (when applied to equipment, systems or
certain work carried out by railway staff).
SAFETY RELATED Having the potential to influence safety (when applied to equipment
or systems).
SAND DRAG A section of line covered in sand or other retarding material on a
dead-end line, or beyond a TRAP POINT or CATCH POINT,
provided in special instances to retard an overrunning movement.
SCHEME PLAN A longitudinal scaled or dimensioned track layout plan that is
produced to depict new or altered signalling.
SCOTCH BLOCK A wedge to prevent the movement of stationary vehicles
SEALED RELEASE An EMERGENCY RELEASE which requires a seal to be broken for
its operation
SEARCHLIGHT SIGNAL A COLOUR LIGHT SIGNAL that can display RED, YELLOW and
GREEN ASPECTS from a single optical assembly. Modern forms
employ LED or fibre optic technology; heritage types change
aspect by placing separate coloured lenses in front of a single
lamp.
SECTION SIGNAL A STOP SIGNAL controlling the entrance to a BLOCK SECTION.
Within a signal box this may be the HOME SIGNAL, STARTING
SIGNAL or ADVANCED STARTING SIGNAL.

TERM DEFINITION
SECTIONAL ROUTE RELEASE ROUTE RELEASING designed to release sequentially, usually one
track section at a time.
SEMAPHORE SIGNAL A SIGNAL which informs drivers by means of the position of a
mechanical arm during daylight and coloured lights at night
SEQUENTIAL LOCKING Locking applied to successive RUNNING SIGNALS to enforce the
replacement of one lever (arm or ASPECT) before the lever
controlling the SIGNAL is REAR is free to be operated. The
locking is non-reciprocal and may be electrical or mechanical.
SERIES BONDED OR BONDING The FAIL SAFE method of BONDING track circuits with rail sections
connected in series, such that a single failure results in the track
circuit showing occupied.
SET (POINTS) Refers to the INTERLOCKING function which controls the movement
of the POINTS to their correct position
SHOULD Used as the primary verb for statements of guidance.
SHUNT OR SHUNTING FRAME A manned control point that is released by another SIGNAL BOX for
local SHUNTING MOVEMENTS. Does not normally regulate
trains or control BLOCK SECTIONS. See also GROUND
FRAME.
SHUNT-AHEAD SIGNAL A type of SUBSIDIARY SIGNAL authorising SHUNTING
MOVEMENTS ahead of a SECTION SIGNAL
SHUNTING MOVEMENT The movement of trains or vehicles other than normal passage along
RUNNING LINES
SHUNTING SIGNAL A SIGNAL provided for SHUNTING MOVEMENTS only
SIDING A line for the stabling of vehicles, loading/unloading, servicing etc.
clear of the RUNNING LINES
SIGHTING DISTANCE (SIGNAL) The distance from a SIGNAL to its SIGHTING POINT
SIGHTING POINT (SIGNAL) The furthest point from a SIGNAL at which the driver can reliably
observe the ASPECT of the signal and/or ROUTE INDICATION
SIGNAL A visual display device which displays instructions or provides prior
warning of instructions regarding the drivers authority to proceed
SIGNAL BOX The building in which the SIGNALMAN is situated together the
control and indication system for the signalling, usually, but not
always, a BLOCK POST
SIGNAL BOX DIAGRAM A diagrammatic representation of the area controlled by a SIGNAL
BOX exhibited for the guidance of the SIGNALMAN
SIGNAL HEAD The section of a COLOUR LIGHT SIGNAL from which the ASPECTS
are displayed.
SIGNAL IDENTIFICATION PLATE The plate attached to a signal post showing the unique identification
of the SIGNAL.

TERM DEFINITION
SIGNAL POST TELEPHONE A telephone provided at a SIGNAL, enabling the driver to have direct
(SPT) communication with the SIGNALMAN.
SIGNAL SIGHTING The activity of deciding on where a SIGNAL should be located for the
optimum approach view by the driver.
SIGNAL STICK The disengaging of a PROCEED ASPECT of a SIGNAL after it has
been used by a train to prevent the re-CLEARance of the signal
until the LEVER or switch controlling the signal has been restored
to NORMAL
SIGNALLER (SIGNALMAN) Person controlling the safe movement of trains.
SIGNALLING FUNCTION A signal, set of points or other part of the train control system.
SIGNALLING PLAN A longitudinally scaled or dimensioned track layout plan showing the
SIGNALLING FUNCTIONs with their identities. It generally
relates to a specific SIGNAL BOX control area and will be derived
from the SCHEME PLAN. Can also be known as a LOCKING
SKETCH.
SIGNALLING SYSTEM The mechanical, electrical and electronic equipment which together
form a system which controls the safe movement of trains.
SIGNALMAN Person responsible for the operation of the signalling system, to
safely control the passage and regulation of trains, usually
located in a SIGNAL BOX. See also SIGNALLER.
SINGLE LINE A RUNNING LINE between two BLOCK POSTs on which trains can
travel in either direction.
SINGLE LINE WORKING Methods of operation introduced so that the traffic of a double line
can pass over one line (which does not have BI-DIRECTIONAL
SIGNALLING) because of engineering work, equipment failure or
an obstruction.
SINGLE SLIP A combination of a DIAMOND CROSSING with two POINTS.
SINGLE YELLOW (ASPECT) Displayed by a COLOUR LIGHT SIGNAL, informs the driver to
expect to see the next MAIN SIGNAL at RED.
SKEW CROSSING A LEVEL CROSSING where the road crosses the railway at an
acute/obtuse angle.
SLIP CONNECTION The connection which permits movement from one line to another at
a DIAMOND CROSSING. See also SINGLE SLIP and DOUBLE
SLIP.
SLOTTING The control of a signal which requires co-operation between two
SIGNAL BOXES or other control points
SNUBBING DEVICE Diode or mechanically operated contacts within the POINT
MACHINE circuitry that are employed to steer the high inductive
load currents (snubbing) away from the point motor. This is in
addition to the clutch mechanism.

TERM DEFINITION
SOLID STATE INTERLOCKING A first generation processor based system for controlling the
(SSI) INTERLOCKING between POINTS and SIGNALs, as well as
communication with lineside SIGNALLING FUNCTIONS.
SPAD SIGNAL passed at DANGER (without authority).
SPARE LEVER In a LEVER FRAME, a lever which is not used for the operation of
any signalling equipment.
SPECIAL SPEED RESTRICTION A sign incorporating a St. Andrews Cross provided on the
BOARD (SSRB) APPROACH TO certain open LEVEL CROSSINGs, indicating a
maximum permitted speed over the crossing. See ADVANCED
WARNING BOARD.
SPEED INDICATOR A trackside sign which marks the beginning of a speed restriction
and indicates the permitted speed.
SPEED OF DIVERGENCE The speed permitted through the DIVERGING ROUTE.
SPLIT DETECTION The proof and indication of the position of a multiple ended set of
POINTS, individually for each POINT END.
SPLITTING DISTANT SIGNALS Two or more adjacent SEMAPHORE SIGNALS or two COLOUR
LIGHT SIGNAL heads providing the driver with information about
the state of a junction BEYOND the next SIGNAL. The
semaphore signals can be placed below a STOP SIGNAL. The
two colour light signal heads are referred to as the main and
offset heads and can incorporate a Stop Signal.
SPRING POINTS UNWORKED TRAILING POINTS which return under spring pressure
to the NORMAL position after the passage of a train in the
TRAILING DIRECTION.
SPT SIGNAL POST A direct line telephone provided adjacent to a signal and linked to the
TELEPHONE controlling signal box.
SPUR (TRACK CIRCUIT) A section of running rail required to be electrically common to a
SERIES BONDED rail, but which is not itself series bonded.
SSI An abbreviated term for SOLID STATE INTERLOCKING.
ST ANDREWS CROSS Signs provided on the road approaches to a LEVEL CROSSING for
the information of road users and on SPECIAL SPEED
RESTRICTION BOARDS.
ST GEORGES CROSS Incorporated in a sign provided on the APPROACH TO certain
AUTOMATIC LEVEL CROSSINGs to inform the driver to regulate
the speed of his train in order to observe the restriction of speed
which applies from the subsequent SPECIAL SPEED
RESTRICTION BOARD. Also referred to as a LEVEL
CROSSING WARNING SIGN.

TERM DEFINITION
STAFF AND TICKET WORKING A signalling system used on a SINGLE LINE and employing a
physical single means of authority (TRAIN STAFF) to occupy a
BLOCK SECTION. If the driver does not take the means of
authority through the section, a written TICKET is issued to
authorise the movement after the driver has seen the train staff.
STAGEWORKS The phased installation and commissioning of signalling equipment,
as part of a large signalling scheme, sometimes a temporary
nature as alterations proceed.
STARTING SIGNAL The first signal IN ADVANCE of a SIGNAL BOX in the direction of
travel.
STATION LIMITS The portion of the line between the HOME SIGNAL and the
SECTION SIGNAL for the same line, worked from the same
SIGNAL BOX. Does not apply on a TRACK CIRCUIT BLOCK
line.
STENCIL INDICATOR A type of miniature ALPHANUMERIC ROUTE INDICATOR (normally
used in conjunction with a SHUNTING SIGNAL), employing a
stencil to form the character(s) to be displayed.
STICK A term often used to describe a function which stores or remembers
a specific condition of the signalling equipment.
STOCK RAIL The fixed rail on each side of the POINTS against which the
SWITCH RAIL must fit closely.
STOP BLOCK A structure fixed to the termination of a RUNNING LINE or SIDING
used to prevent further movement of the train.
STOP BOARD A sign where a driver must stop his train.
STOP SIGNAL Any MAIN SIGNAL capable of showing a DANGER ASPECT or
indication.
STRAIGHT AHEAD ROUTE The non-diverging (and normally the fastest) route from a
JUNCTION SIGNAL.
STRETCHER A bar connecting the two SWITCH RAILs in a POINT END, keeping
them in the correct position relative to each other. See also LOCK
STRETCHER.
STRIKE-IN POINT (SIP) The position on the APPROACH TO an AUTOMATIC LEVEL
CROSSING or other installation at which a train initiates the
operating sequence
SUBSIDIARY SIGNAL An additional SEMAPHORE SIGNAL controlling SHUNTING
MOVEMENTS and movements onto OCCUPIED tracks
SUPPLEMENTRY DETECTOR An additional device for the DETECTION of POINTS in association
with a SUPPLEMENTARY DRIVE.
SUPPLEMENTRY DRIVE An additional drive connected to the SWITCH RAILS of a set of
POINTS.

TERM DEFINITION
SUPPRESSION (AWS) Inhibition of the operation of AWS track equipment for movements to
which it does not apply.
SWINGING OVERLAPS The ability to maintain the OVERLAP free of locking where there are
FACING POINTS and a choice of overlap exists, thus enabling
late selection of the overlap while the train is approaching.
Usually associated with TIME OF OPERATION LOCKING and
CONDITIONAL LOCKING requirements. Will not normally be
used where the signalling is controlled from a LEVER FRAME.
SWITCH DIAMOND A type of DIAMOND CROSSING with moveable SWITCH RAILs in
place of fixed rails. Also known as elbows.
SWITCH RAIL The moving portion of rail on each side of a set of POINTS
SWITCHES & CROSSINGS (S&C) The generic term used to represent all the ironwork associated with a
set of POINTS or a DIAMOND CROSSING.
TABLET A particular form of TOKEN.
TAIL CABLE A cable between a location case or equipment room and signalling
equipment.
TAIL LAMP The red light at the rear of a train use to indicate that the train is
complete.
TBTC Transmission based train control. Trains controlled by cab displays
with no line side signalling. Can be driven automatically or
manually.
TEMPORARY APPROACH A signalling control built into the SIGNALLING SYSTEM and applied
CONTROL when it is necessary for drivers to control the speed of their trains
due to engineering works or other operational requirements.
TEMPORARY SPEED A speed restriction that has been imposed for a short period.
RESTRICTION (TSR)
TERMINAL PLATFORM A platform that serves a dead-end line. See also bay platform.
TERMINAL STATION A station that the end of a line.
TERMINATION INDICATOR A trackside sign denoting the end of a TEMPORARY SPEED
RESTRICTION.
THEATRE INDICATOR An alternative term for MULTI-LAMP ROUTE INDICATOR.
THREE ASPECT SIGNAL A COLOUR LIGHT SIGNAL capable of displaying three ASPECTS.
THROUGH ROUTES An alternative term for OVERRIDE (commonly used on the Western
Region) where the signalling is set work automatically on the
main route through an interlocking area..
THROUGH STATION A station mainly for non terminal lines.
TICKET A written form handed to a driver by the SIGNALMAN to authorise
entry to a SINGLE LINE section (only valid if the driver has been
shown the TRAIN STAFF for that section at the same time).

TERM DEFINITION
TIME DIVISION MULTIPLEX An electronic system used for transmitting a number of data
(TDM) channels over a single pair of wires. Not normally used for VITAL
INTERLOCKING functions.
TIME OF OPERATION LOCKING The locking of FACING POINTS such that, if a train overruns the
protecting SIGNAL, the POINTS will not be able to move while
there is the possibility that the train that has SPADed the signal
will reach the points before their movement has been completed.
TIME RELEASE A device or control used to prevent the operation of a signalling
function until after the lapse of a specified time.
TOE The front end of a SWITCH RAIL.
TOKEN A generic term for any physical item that is issued to a train driver to
authorise the train onto a SINGLE LINE.
TOKEN INSTRUMENT A generic term for an instrument which can contain one or more
TOKENs and which controls the release of the TOKENs. See
also ELECTRIC KEY TOKEN INSTRUMENT.
TOKEN SECTION A BLOCK SECTION or other designated section of RUNNING LINE
controlled by a TOKEN.
TOKEN TRANSFER MAGAZINE A magazine that can be temporarily attached to a TOKEN
INSTRUMENT to permit TOKENs to be transferred from one
token instrument to another. This enables the transfer of Tokens
between instruments without affecting the operational use of the
token system.
TOKENLESS BLOCK A method of working a SINGLE LINE using BLOCK INSTRUMENTs
but without using a physical TOKEN, CONTINUOUS TRACK
CIRCUITs or other means of automatic train absence detection.
TOLLERTON CONTROL A timing delay incorporated into the operation of TRACK CIRCUITs
where an incorrect sequence for track circuit clearance could give
rise to a hazardous INTERLOCKING release.
TRACK CIRCUIT (TC) An electrical device using the rails as part of an electric circuit, which
proves the absence of trains on a defined section of line.
TRACK CIRCUIT BLOCK A method of working trains in a section of line where safety is
ensured by the use of TRACK CIRCUITs or other means of
automatic train absence detection and without the use of BLOCK
INSTRUMENTs or any form of physical TOKEN.
TRACK CIRCUIT INTERRUPTER A track mounted device normally positioned at CATCH or TRAP
(TCI) POINTS which maintains a TRACK CIRCUIT or other TRAIN
DETECTION device in its OCCUPIED state after the passage of
a vehicle which may have been derailed.
TRACK CIRCUIT MINIMUM The minimum length of a TRACK CIRCUIT, which has to be greater
LENGTH than the longest wheel-base of any vehicle required to be
detected.

TERM DEFINITION
TRACK LOCKING The locking of a signalling function when a TRACK SECTION over
moveable infrastructure (e.g. POINTS) is OCCUPIED.
TRACK SECTION A portion of railway track having fixed boundaries and for which the
TRAIN DETECTION SYSTEM provides information on its state of
occupancy to the signalling system.
TRAILING (DIRECTION) The direction of rail traffic over POINTS where the train meets the
HEEL of the SWITCH RAIL first (the train having no choice of
route).
TRAILING POINTS POINTS which joint two converging ROUTES.
TRAIN DETECTION SYSTEM Equipment and systems forming part of, or providing input to, the
SIGNALLING SYSTEMS to detect, either:
the presence or absence of vehicles within the limits of a track
section, or
that a train has reached, is passing or has passed a specific
position.
Where required, a train detection system may additionally detect the
direction in which a train is travelling.
TRAIN ON LINE (TOL) BLOCK INSTRUMENT indication showing that a train has
OCCUPLIED the BLOCK SECTION or that the BLOCK SECTION
is obstructed.
TRAIN OPERATED POINTS A generic term for TRAILABLE POINTS which are continuously
driven to one position such that FACING movements will always
pass through them in the same direction. A common type is the
HYDRO-PNEUMATIC POINTS.
TRAIN PROTECTION WARNING A system of aerials located at a signal or on the approach to a signal
SYSTEM (TPWS) or speed restriction to reduce the risk of collision or derailment in
the event that the red aspect or speed restriction is not complied
with. Trains are fitted with receivers to operate the train borne
equipment (such as brakes and visual indicators). System is not
fail safe
TRAIN READY TO START (TRTS) An INDICATOR in the SIGNAL BOX to indicate to the SIGNALMAN
INDICATOR to CLEAR the PLATFORM STARTING SIGNAL. Can also be
known as TRS.
TRAIN READY TO START (TRTS) The means by which station staff or train crew inform the
PLUNGER SIGNALMAN that the train is ready to depart.
TRAIN STAFF A particular type of TOKEN.
TRAINCREW OPERATED A crossing equipped with BARRIERS (with or without ROAD
BARRIERS [TMO(B)] TRAFFIC SIGNALS) and operated by a member of the train crew
or other nominated person.

TERM DEFINITION
TRAINCREW OPERATED A crossing, normally equipped with GATEs, where the means of
CROSSING (TMO) protection for the train and road users is operated by the train
crew.
TRAP POINTS FACING POINTS provided at an exit from a SIDING or converging
line to de-rail an un-authorised movement, thus protecting an
adjacent RUNNING LINE (also TRAILING POINTS inside the
entrance to a loop line).
TREADLE A MECHANICAL or electrically operated device to detect the
presence or passage of a train at a specific location.
TUNNEL SIGNAL A SIGNAL which, if at DANGER, would cause a train to stop wholly
or partly within a tunnel.
TURNOUT A point end.
TURNOUT SPEED The speed permitted through a FACING POINT when SET for the
DIVERGING ROUTE.
TWO ASPECT SIGNAL A COLOUR LIGHT SIGNAL capable of displaying two ASPECTS.
TWO ASPECT SIGNALLING A system of colour light signalling normally employing red/green
TWO ASPECT SIGNAL(s) that are preceded by yellow/green
REPEATER SIGNAL(s).
UNDER CLEARANCE The gap between the permanent way stretcher bar and the stock rail.
UNDER ROAD CROSSING (URX) A buried service route passing underneath the road carriageway, for
example at a LEVEL CROSSING.
UNDER TRACK CROSSING (UTX) A buried service route passing under the tracks below the level of the
underside of the sleepers or track slab. This excludes services
laid through a bridge span or roadway.
UNPROTECTED WRONG SIDE A WRONG SIDE FAILURE where no other part of the signalling
FAILURE system provides protection.
UNWORKED POINTS POINTS not controlled from a SIGNAL BOX or GROUND FRAME.
UPPER QUADRANT A term applied to a SEMAPHORE SIGNAL whose CLEAR position is
designated by the arm above the horizontal.
USER WORKED CROSSING LEVEL CROSSING protected by GATEs or BARRIERs, operated by
(UWC) the user. It may be equipped with a telephone and/or
RED/GREEN LIGHTS.
VEHICLE OVERHANG The distance measured parallel to the rail from the centre of the
outermost wheel on a vehicle to the nearest extreme end of the
vehicle.
VITAL A description applied to equipment whose correct operation is
essential to the integrity of the signalling system. Most vital
equipment is designed to FAIL-SAFE principles; a WRONG SIDE
FAILURE of vital equipment could directly endanger rail traffic.

TERM DEFINITION
WARNING BOARD A board on the APPROACH TO a TEMPORARY or EMERGENCY
SPEED RESTRICTION ahead, placed at a distance before
commencement to provide adequate BRAKING DISTANCE.
WARNING ROUTE A route from one MAIN SIGNAL to the next signal where the full
OVERLAP is not available.
WARNING SIGNAL A SEMAPHORE SIGNAL arm, normally located below the SECTION
SIGNAL, which, when cleared, indicates the block section to the
next HOME SIGNAL does not have a full OVERLAP.
WELWYN CONTROL In Absolute Block, it prevents the Signaller from accepting a second
train without the first having occupied and cleared the HOME
SIGNAL BERTH TRACK CIRCUIT. See also HOME NORMAL
CONTROL and INTERLINKING.
WHISTLE BOARD A sign to inform the driver to sound the whistle or horn
WICKET GATE (LEVEL A gate, which may be controlled from a SIGNAL BOX or GATE BOX,
CROSSING) used to regulate the passage of pedestrians over a railway line
WICKET GATE LEVER A LEVER which, when REVERSE, will lock the WICKET GATE(s)
closed. Not interlocked with the signalling.
WIDE TO GAUGE POINTS A Point End where the two Switch Rails are not connected by
Stretchers. There are two ways in which this can be applied:
Trap Points where the two switch rails move in opposite
directions both open in the Normal position; both closed in
the Reverse position. Used where it is required that a derailed
train keeps closely to the track alignment.
A Point End forming part of two Crossovers, where each switch
rail is operated by a separate Point Machine.
WIG-WAG Colloquial term for ROAD TRAFFIC SIGNALS.
WRONG DIRECTION Opposite to the normal direction of rail traffic on a particular line
WRONG SIDE FAILURE A failure which results in the protection provided by the signalling
system being reduced or removed. See PROTECTED WRONG
SIDE FAILURE and UNPROTECTED WRONG SIDE FAILURE
YELLOW (ASPECT) See SINGLE YELLOW (ASPECT)
YELLOW BOND A JUMPER cable that is necessary to ensure the electrical integrity
of a TRACK CIRCUIT that is fully or partially parallel bonded.
YELLOW SHUNT SIGNAL A type of SHUNTING SIGNAL which applies only to movements in
the direction(s) for which the SIGNAL is CLEARed, other
movements being able to pass the SIGNAL without it being
cleared. Can also be a GROUND POSITION LIGHT SIGNAL
using a yellow light in place of the red light
YODALARM Proprietary term for a LEVEL CROSSING AUDIBLE ALARM.

IRSE 2011
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