A comprehensive guide to terms used by Intelligent Transport Systems
85th percentile - The speed at or below which 85 percent of all vehicles are observed to travel under free-flowing conditions past a monitored point.
acceptance - The agreement that a system complies with the requirements of a design/specification and is compliant with national standards.
Advanced Motorway Indicators (AMI) - Lane specific VMS, used for Variable Mandatory Speed Limits and Lane Closures on Smart Motorways.
Advanced Stop Line (ASL) - An area ahead of the vehicular stop line for cyclists.
all-purpose road - Road for the use of all classes of traffic.
all red - A condition of traffic signals where all phases display a red signal.
amber - The particular colour in the yellow part of the spectrum used in traffic signals. The same as the term “yellow” used in European specifications.
amber dilemma - Issue experienced by drivers who are approaching a set of signals in excess of 35mph when the signals start to change from green.
approach - That part of an arm which carries traffic towards the junction.
arm - One of the highways radiating from a junction.
arrow - A signal aspect with a symbol indicating a direction.
arterial reversion - Reversion to a selected stage in the absence of demands.
aspect (signal aspect) - A single optical unit, which, when illuminated, displays a single colour or symbol.
at-grade - At the same level as the surface of the carriageway.
audible signal - A device producing a sound to indicate right of way to pedestrians or cyclists.
Automatic Number Plate Recognition (ANPR) – A video analytics technology capable of automatically ascertaining vehicle registration details from video images of passing vehicles.
availability - The availability of a system is the amount of time the system is functioning and available for operational use expressed as a percentage of the total time.
backing board - A panel mounted behind or around a signal head to increase contrast and improve visibility (referred to as ‘background screen’ in BS EN specifications).
base seal – The traditional method of sealing the base of cabinets from water or vermin using dry sand and epoxy resin (See also elevated cabinet base).
blackout period - A part of the signalised crossing sequence when neither the red nor green person symbol is illuminated.
box sign - A regulatory sign (such as a prohibited movement sign) designed to be mounted alongside a signal head within an aspect housing.
bracket - A device for mounting a signal head or other equipment on to a supporting structure such as a signal pole, mast arm or gantry.
bus priority - A facility for reducing delay to buses by providing a hurry call like capability to prioritise the transit of buses through a junction, also referred to as Public Service Vehicle (PSV) priority.
cabinet – A box installed on-street to contain a traffic signal controller or other equipment.
Cableless Linking Facility (CLF) mode – A method of control available in a TSC for co-ordinating the timings with adjacent TSCs by using traffic plans in each TSC synchronised to clock settings.
cabling - The wiring installed on-street to connect a traffic signal controller with the signal aspects and other equipment.
call - The placing of a demand for a stage or phase.
call / cancel - The function of a detector which calls a stage or phase when occupied for a specified time but for which the demand is cancelled if it subsequently becomes unoccupied for a specified time before the demand matures. Can be used for vehicular, pedestrian, cyclist or other road user demands.
capacity - The maximum flow that can proceed through a certain point in a given period of time.
carriageway - A way constituting or comprised in a highway, being a way (other than a cycle track) over which the public have a right of way for the passage of vehicles.
CCTV - Closed Circuit Television.
CDM Regulations - The Construction (Design and Management) Regulations 2015.
central reserve - A central island separating the two halves of a dual carriageway.
chamber – Part of the underground duct network to provide access to cables and equipment.
classified count - A count where flows for different classes (types) of vehicle (motorcycles, cars, buses, LGV, HGV etc) are recorded separately.
COBA - DfT computer program for Cost Benefit Analysis.
condition - The pattern of illumination of aspects of a signal head at a point in time.
configuration – Software and hardware customisation of a traffic signal controller to achieve the required functionality for a specific site.
conflict - At a junction, movements which cannot proceed at the same time safely are in conflict.
conflicting phases - Phases which control movements which are in conflict, I.E. where traffic movements would collide if both phases were to operate simultaneously. (See also ‘opposing phases’)
control bits – Incoming UTC commands to a TSC, includes stage appearance, phase demands and ancillary commands, such as Real Time Clock synchronisation.
controlled crossing – Zebra and signal-controlled crossings where users have precedence over vehicular traffic.
controller - Apparatus that controls and switches traffic signals.
co-ordination - An arrangement which relates the timings of the signals at one installation with those at neighbouring installation(s).
cycle - One complete sequence of the operation of traffic signals.
cycle time - The time taken to complete one cycle.
cycle track - A way constituted or comprised in a highway being a way over which the public have right of way on pedal cycles only, with or without the right of way on foot (section 329, Highways Act 1980).
demand - Request for right of way registered by traffic via a detector.
demand dependent (DD) - A stage in a signal cycle or specific stage movement which is only selected when a demand for it is registered.
Department for Transport (DfT) – Government department responsible for transport in the UK.
Design File - A file of basic information and certification for a scheme, produced during the design process to provide a record of the development of the scheme, the decisions made and the safety considerations.
Design Organisation - The organisation commissioned to undertake the various phases of scheme preparation and supervision of construction. During the course of scheme preparation and construction, the identity of the design organisation may change.
desire line – The actual route taken by users that accords with their natural route, usually refers to pedestrian use at junctions or crossings.
detector - Equipment detecting traffic that initiates a demand or extension. Different types are used to detect different road user types.
detector loop - One or more turns of wire installed in the road surface forming part of a vehicle detector which relies on the electromagnetic changes caused by a vehicle.
detector unit - The part of the detector which is connected to a detector loop or transducer and produces an output when a vehicle is detected.
dimming - The automatic reduction in brightness of signal aspects during hours of darkness to reduce glare to road users (see also solar cell).
DMRB - Design Manual for Roads and Bridges.
ducting - The system of underground ducts carrying the cabling at a junction.
duplicate primary signal - A second primary signal mounted on the right-hand side of the carriageway.
early cut-off - A condition in which one or more traffic streams, that were running during the preceding stage, are stopped whilst one or more other traffic streams are allowed to continue moving.
early start - A condition in which one or more traffic streams are permitted to move before the release of other traffic streams, which are then permitted to run with them during the subsequent stage (See also ‘late start’).
effective green - For a given actual green period, the length of green time, which when multiplied by the saturation flow, represents the maximum amount of traffic which will be able to pass in that green period.
elephant feet – Road marking to Diagram 1055.3 to demarcate cycle routes at parallel crossings and within signalised junctions.
elevated cabinet base – Modern method of sealing cabinet bases by using a glanding tray to provide an effective barrier to water and vermin.
engineers handset – A handheld device used to interrogate and alter settings in a Traffic Signal Controller (TSC) usually by plugging in to a dedicated port within the TSC cabinet.
equestrian crossing - Crossing for ridden horses, which may use far-side or nearside aspects.
exit - At a junction, the portion of an arm which carries traffic away from the junction.
extension - Continuation of the green signal that results from a request made by a vehicle or pedestrian that has right of way. (May also be applied to a red signal.)
FAT - Factory Acceptance Test.
fault log – An intrinsic element within each TSC, to record fault issues. Entries in the fault log range in severity and may result in the TSC shutting down if required for safety reasons. The fault log can be viewed via the engineers handset to assist in fault rectification and can also be used to notify the RMS automatically.
F bits – UTC control bits for stage selection, typically F1, F2 etc in TSC, but FA, FB etc in UTC.
feeder pillar – Enclosure for electrical supply, may house an electricity meter as well as the cut-out, circuit breakers etc.
filter arrow - A green arrow which appears with a red (or amber or red/amber) signal to give right of way to a specific movement.
fixed time mode - A method of control available in a TSC where the duration of the red and green signals and the length of the cycle is pre-programmed and not reliant on vehicle detection.
fixed time plan – A predefined timing plan usually in UTC or CLF modes. Different plans may be used at different times of day or to react to traffic incidents.
footpath - A way over which the public have a right of way on foot only, not being a footway.
footway - A way, comprised in a highway which also comprises a carriageway, over which the public has a right of way on foot only.
functional specification - A type of system specification where the functions of the system are specified rather than the method of achieving those functions.
gantry - A frame in the shape of a portal used to mount signs or signals.
gap - The difference in time or space between the back of a vehicle and the front of the following vehicle.
gap accept – Normally a right-turning vehicle movement during a gap in oncoming, conflicting traffic.
gap out – In Vehicle Actuated modes, a phase termination caused when extensions cease.
gating - The use of traffic signals to restrict the flow of traffic at a point with the aim of improving the efficiency of traffic flow at a downstream point.
G bits – UTC reply bits to indicate currently active stage, typically G1, G2 etc in TSC, but GA, GB etc in UTC.
ghost island – An at-grade area marked out on the highway, usually at a road junction, shaped and located so as to direct traffic movement.
green arrow - A green aspect consisting of an arrow symbol, to indicate permitted direction of movement.
green wave - A control strategy for a linear system of traffic signals which attempts to synchronise the start of green at a junction with the arrival of a platoon from the preceding junction.
guard railing - Railing installed on footways and islands to direct pedestrians.
Hazard List - As part of a Risk Analysis, a list of features of a scheme which could have an implication for health and safety.
headway - The difference in time or space between the front of a vehicle and the front of the following vehicle.
Health and Safety Plan - A document (as required by the CDM Regulations) which contains details of the scheme, an assessment of risks to health and safety to persons involved in, or affected by, the construction of the scheme, and arrangements for ensuring, as far as is reasonably practicable, the health and safety of such persons.
High Friction Surfacing (HFS) – Surface treatment to improve the skid resistance of vehicles on the highway, at traffic signals usually applied on the approach to stop line locations.
high speed - For the purposes of traffic signal installations, a road where the 85th percentile motor traffic approach speeds at a junction are 35mph (56km/h) or above.
highway - Way over which the public has a right to pass. The right may be restricted to specific classes of vehicle or user.
Highways Agency (HA) - former name of National Highways
Highways England (HE) - former name of National Highways
hood - A device mounted above a signal aspect to prevent incident light falling on the lens and reducing contrast and/or to prevent the aspect being seen by road users for whom it was not intended.
IET - Institution of Engineering and Technology.
IHE - Institute of Highway Engineers.
immediate movement (IM) - A stage in a signal cycle or specific stage movement which will operate irrespective of if a demand currently exists.
Impact Electrical Isolation (IEI) – Equipment to electrically isolate roadside structures in the event of being struck by an errant vehicle.
indicative green arrow - A green arrow indicating that vehicles may proceed in the direction shown which is also covered by a full green signal. Opposing traffic has been stopped.
In-station – UTC equipment located within the UTC control centre used to communicate with the individual Out-stations in each TSC cabinet.
Integrated Traffic Management (ITM) – Operational link between ramp metering installation and local traffic signal controller.
Intelligent Transport Systems (ITS) - Systems and equipment which provide solutions to Improve Safety, Increase Capacity, Inform Users and Manage Assets.
Intelligent Transport Systems Engineer - A person with specialist skills, knowledge and experience for the design, commissioning, operation and management of ITS equipment.
Inter-green period – Critical safety period between the end of the green signal for one phase, and the beginning of the green signal on another phase.
Inter-green matrix – A matrix of inter-green timings between all conflicting pairs of phases.
Inter-stage period - The period between the end of one stage and the start of the next stage.
invitation to cross - The period of display of a steady green walking figure to pedestrians at traffic signals.
island - Raised area on the highway, usually at a road junction, shaped and located so as to direct traffic movement.
ISO 9001 - One of the ISO 9000 series of international standards concerned with Quality Management and Quality Assurance with specific reference to the quality systems where a supplier’s capability to design and supply a conforming product needs to be demonstrated.
isolated control - Control of a signalled junction where the timings are not related to neighbouring junctions.
junction - The meeting point between two or more roads. (Note: no distinction is usually made between a junction being where roads meet, and an intersection being where roads cross). Defined in the Regulations as ‘a road junction’.
lamp - The light source in a signal aspect, usually halogen or LED.
lamp monitoring - A system of checking within a controller that lamps are operating.
lane - A section of an approach marked for the use of a single file of vehicles.
lane control signals - Overhead signals indicating the permitted direction of movement.
late start - A condition in which one or more traffic streams are held back, whilst others are permitted to move, before the held streams are then permitted to run with them during the subsequent stage (See also ‘early start’).
LED - Light Emitting Diode, a solid-state light source now commonly used in lamps.
lens - The translucent face of a signal aspect which supplies the colour and symbol (if required) and which may control the light distribution of the aspect.
Life Cycle Costing - The costing of a system, including the costs of operation, maintenance and decommissioning, as well as design and construction.
link - In a network, a connection between nodes. In traffic networks, links between junctions may be defined for particular directions, movements or vehicle types.
LINSIG - A computer program for the analysis of traffic signal operation.
local control - A form of control at a signal installation which is not subject to influences from other junctions or area control systems.
loop detector - A detector which operates by analysing the electromagnetic effects on a buried loop of wire caused by the presence or passage of a vehicle.
loop feeder - Cable connecting a detector loop to its detector unit.
lost time - The time during a cycle which cannot be used as effective green to one or more vehicular phases.
main road stage – Traditional reference to the start-up stage and the revertive stage in Vehicle Actuated modes.
Manual mode – A method of control available in a TSC controlled by pressing stage selection switches on the manual (police) panel by a traffic engineer or police officer.
mast arm - A cantilevered arm to allow a sign or signal to be mounted above a carriageway.
maximum green - The time that a green signal to vehicles can continue after a demand has been made by traffic on a conflicting phase.
Message Sign 3 (MS3) - Alphanumeric Variable Message Sign
Message Sign 4 (MS4) - Full matrix Variable Message Sign
method of control – The different modes of operation available within a Traffic Signal Controller, such as manual or fixed time etc.
Microprocessor Optimised Vehicle Actuation (MOVA) - A method of control strategy based on minimising stops and delays which maximises capacity at isolated signals. Often referred to as a UTC type mode, but plans are held locally within the MOVA sub-system in the TSC itself.
minimum green - Duration of the green signal, following the extinction of a red-amber signal, during which no change of signal lights can occur.
movement - The traffic taking a specific route through a junction from a defined entry to a defined exit.
National Highways - The highway authority for the Strategic Road Network in England.
national sequence - The sequence of indications of traffic signals which are prescribed by national legislation or regulation.
near-side indicator – Pedestrian signal used at PUFFIN style crossings which is installed prior to the crossing.
NMCS - National Motorway Communication System.
node - In a traffic network, a junction or other point where it is convenient to identify as the end of a link.
Non-Motorised User (NMU) – Road users not in motor vehicles, such as pedestrians and cyclists (See also Vulnerable Users).
Office of Rail and Road – Government regulator for rail and road transport.
offset - The difference in time between a specific point in the cycle at a junction and a reference point.
opposing phases - Phases which control movements which operate at the same time as each other but are in essence conflicting, I.E. ahead movements on two opposite approaches which run at the same time (See also ‘conflicting phases’).
Origin / Destination (OD) – A traffic survey used to comprehensively record the quantity of vehicles making the different permutations of routes through a junction for a defined period of the day. These should be classified counts to provide a breakdown by vehicle types.
OSCADY - A computer program for the analysis of isolated traffic signals developed by the TRL.
Outstation Telemetry Unit (O.T.U.) – An interface unit situated within a TSC cabinet to operate with UTC.
overlap - Phases which run in successive stages (e.g. late start, early cut-off).
oversaturation - A traffic condition at traffic signals where demand exceeds capacity.
Pan, Tilt, Zoom (PTZ) – Type of CCTV camera which can be remotely controlled to adjust the view achieved by the camera.
Parallel crossing – A Zebra crossing with a segregated cycle crossing.
parallel stage streams - Two or more complete sequences of stages within the same controller which operate at the same time enabling two junctions or parts of a junction to be controlled with or without interaction between them.
pcu - Passenger Car Unit, the basic unit of traffic flow equal to the equivalent of a typical car.
pedestrian demand unit – The pushbutton used by pedestrians to place a demand for a pedestrian phase.
pedestrians per hour (pph) – Number of pedestrians using a facility, typically average of 4-hour peak.
pedex – Modern alternative to Pelican crossings for far-side style stand-alone signal-controlled pedestrian facility.
Pelican crossing - A pedestrian crossing using far-side pedestrian indicators with a flashing amber/flashing green period during which vehicles are permitted to move subject to giving way to pedestrians. Under the Regulations, may no longer be installed in England, Scotland or Wales, although existing sites may remain until the end of their life. May still be installed in Northern Ireland.
phantom - A false impression that an aspect is illuminated caused by incident light being internally reflected back through the lens.
phase - ‘Sequence of conditions applied to one or more streams of traffic which, during the cycle, receive simultaneous identical signal indications’ (TP56) ‘Set of conditions that fixes the pattern of movement and waiting for one or more traffic streams during the signalling cycle.’ (BS 6100 241 7509). By extension, the equipment within a controller which controls a phase.
phase diagram - A diagram showing (as horizontal lines) the sequence of conditions of each of the phases at a traffic signal junction.
platoon - A group of vehicles moving together where the behaviour of each vehicle is influenced by the vehicle in front.
platoon dispersion - The tendency for platoons to extend and break up under free running conditions.
pole – Column used to mount traffic signal equipment on, traditionally 144mm diameter steel construction, now increasingly using aluminium and composite materials in various diameters.
pole cap assembly – The electrical termination assembly which was traditionally located at the top of the pole under a plastic cap to protect it from the weather.
portable signal - A traffic signal designed to be moved from place to place, as prescribed in Diagram 3000.1 of TSRGD.
Practical Reserve Capacity (PRC) - The difference between the capacity of a junction and the current demand (usually expressed as a percentage).
presence - A target being present within the detection zone.
pre-signal - A traffic signal installed in advance of a junction to control access to the junction for a particular movement or type of vehicle in a segregated lane.
primary signal - A signal head close to the stop line normally mounted on the left-hand side of the carriageway.
Programmable Read Only Memory (PROM) - A non-volatile storage device for programmes used in electronic devices.
Public Service Vehicle (PSV) priority – Refer to bus priority.
PUFFIN crossing - A pedestrian crossing using nearside light signals.
Push Button Unit (PBU) - A housing for a button which may be pressed by pedestrians, cyclists or equestrians to register a demand.
PV/PX – Pedestrian crossing vehicle/crossing control bits, used to synchronise pedestrian crossings with the operation of an adjacent signalised junction.
Quality Assurance - A method of assuring that the features and characteristics of a product or service satisfy stated or implied needs.
Quality Plan - A document required under a Quality Assurance scheme which defines responsibilities and procedures in a project to ensure that the QA requirements are met.
queue - A stationary or slow-moving file of traffic where the progress of a vehicle is determined by that of the preceding vehicle.
queue detection – Vehicle detection used to detect the presence of a queue, may be used as part of MOVA or to introduce a specific mitigation traffic management plan.
raised table junction – Where the carriageway surface level is raised across the entire junction area, usually to the same height as the footway. The aids pedestrian connectivity and is intended to lower vehicle speeds.
red lamp monitoring - Lamp monitoring of some or all of the red lamps at a junction.
Red Light Enforcement (RLE) – Camera system to produce evidence of traffic violations at traffic signals, used to improve compliance rates and safety.
refuge - An island where pedestrians may wait.
regulatory sign - A sign indicating a traffic regulation (such as a prohibited movement).
reliability - A measure of the ability of a system, subsystem or item of equipment to operate without faults usually expressed as the Mean Time Between Failures (MTBF).
Remote Monitoring System (RMS) - A system which is notified of entries in TSC fault logs to automate fault reporting to the incumbent maintenance contractor.
reply bits – Outgoing UTC replies from a TSC, includes stage appearance and phase demand confirmations and ancillary data such as equipment fault classifications.
reserve capacity - The difference between the capacity of a junction and the current demand (usually expressed as a percentage of the current demand).
Residual Current Device (RCD) - An electrical safety device which compares the current entering a circuit with the current leaving it and which will isolate the circuit if the difference (the residual current) exceeds a given value.
right of way – At traffic signals, the right of priority attached to traffic moving in a particular direction, temporarily given to traffic by signals, signs, pedestrian crossings or other means.
ripple change – A stage change where constituent phase(s) appears in both stages and therefore stays operating through the inter-stage period.
Risk Assessment - An analysis of the risks to health and safety involved in the construction, operation and maintenance of a scheme. The Risk Assessment included in the Health and Safety Plan required by the CDM Regulations deals primarily with the construction phase of the scheme. Risk Assessments are also required for the operation and maintenance aspects of a Traffic Control and Information system.
road - Any highway, and any other road to which the public has access, including bridges over which a road pass.
road hump – A traffic calming feature consisting of a raised section of carriageway perpendicular to the flow of traffic.
road marking - A sign consisting of a line, mark or legend on a road.
Road Safety Audit (RSA) - A formal procedure for the independent evaluation of highway schemes before implementation to identify potential safety hazards which may affect road users and to suggest measures to eliminate or mitigate those problems.
run - A phase is said to be running when it is displaying a green signal. A stage is said to run a phase if that phase displays a green signal during that stage.
Safety Case - The formal presentation of evidence that a system will be safe throughout its life cycle. It will include a Risk Assessment and will be reviewed at various stages in the life cycle of the scheme.
Safety Review - An independent review of the safety aspects of a system carried out after the preliminary design stage and again after the detailed design stage. These reviews run in parallel with, and may be combined with, the Stage 1 and Stage 2 Road Safety Audits extended to cover the control and operational aspects of the proposed system.
SAT - Site Acceptance Test.
saturation flow - The maximum flow (usually expressed in pcu per hour) obtained at a stop line during green from a discharging queue.
SCOOT - Split, Cycle, Offset Optimisation Technique, a UTC method of control which uses real time traffic data to minimise stops and delays for UTC controlled areas.
SDE - Speed Discrimination Equipment, a VA control strategy for high-speed roads which discriminates vehicles travelling above a given speed threshold.
secondary signal - A signal beyond the stop line and the primary signal, which duplicates the display at the primary signal.
see through – A safety issue where a user can see a signal provided for a different movement, which may lead to the risk of them reacting to the wrong green signal.
shuttle working - A system where signals are used to control a one-way section of carriageway operating in alternating directions.
signal - A dynamic indication presented to road users.
signal display - The combination of illuminated aspects in a signal head which provides a control instruction to traffic.
signal head - A combination of signal aspects which together provide all the signal displays required for the control of one or more traffic streams at the same stop line.
signal mask – A blanking plate with a symbol cut-out (arrow, pedestrian, cycle etc) fitted to the signal optics to provide a specific instruction to users.
signal pole - Support provided at a traffic signal installation for one or more signal heads.
signal sequence - The sequence of displays shown by a signal head.
signs authorisation - The process of granting authorisation for the use of traffic signs (including traffic signals and road markings) which are not prescribed in the relevant regulations.
Site Layout Drawings (SLDs) – Set of traffic signal design drawings, depending on scheme complexity / Highway Authority, could consist of a single drawing to a large number.
slot cutting – The process used to form a cut slot in the carriageway surface, by using a large water-cooled disc cutter, to install an inductive vehicle detection loop.
solar cell - A light sensitive device mounted on signals to initiate dimming of the lamps during darkness.
special conditioning – Manual coding within the TSC software configuration to achieve a functionality which is not achievable using the pre-defined facilities of the configuration / system capability.
Speed Assessment (SA) - A VA safety strategy for high-speed roads which affects the changing of the signals according to the speed of approaching vehicles.
split - The division of available green time within a signal cycle between stages.
SRS - System Requirements Specification.
stage - The period within a traffic signalling cycle that gives right of way to one or more particular traffic movements. A stage starts when the last of its associated phases commences and ends when the first of its associated phases terminates.
stage diagram - A diagram for a signalled controlled junction showing by means of arrows those movements permitted in each of the stages.
Standard Details (SD) – Drawings used to illustrate how generic items are constructed, such as civil’s elements for sub-surface ducts or pole foundations.
stand-alone - Refers to a crossing facility provided away from a signal-controlled junction, where traffic is stopped only for the purpose of enabling pedestrians, cyclists or equestrians to cross the carriageway.
start displacement - The time interval between the start of actual green and the start of effective green.
start-up sequence - The controlled order through which signals progress from the off/standby mode to normal operation.
Statutory Undertakers - Bodies that have been given statutory powers in relation to functions that are of a ‘public’ character, including private bodies such as those providing electricity, gas, water, sewerage and electronic communications.
steel wire armoured (SWA) – An electrical cable with inbuilt metal sleeving to protect against mechanical damage to the cable.
storage - Ability for vehicles (usually right turning) to wait within the junction.
Strategic Road Network (SRN) – Motorways and ‘A’ roads in England which are operated by Highways England (HE).
stream – Refer to parallel stage stream.
SVD - Selective Vehicle Detector - a detector which responds only to certain vehicles identified by their characteristics or by an electronic tag.
SVD – Stopped Vehicle Detector – a detector used to ascertain if vehicles are stationary, typically within a Smart Motorway All Lane Running section.
swept path – Analysis of vehicle tracking when turning, using computer simulation to inform the safe geometric design of the carriageway, especially for larger vehicles, such as heavy goods vehicle or buses.
takeover – The agreement to include an asset within a contractual arrangement, usually equipment purchase or maintenance provision after successful installation.
tactile indicator - A rotating cone indicator which indicates the presence of a green signal for the benefit of visually impaired pedestrians.
tactile paving - A type of textured paving, the blister pattern of which can be identified by visually impaired people to indicate the location of a crossing facility.
temporary signal - A traffic signal using the same type of signal equipment as permanent signals, but which is installed for a limited period of time and mounted in a temporary fashion, for example in a concrete block support.
tidal flow – A traffic management tool to allocate the direction of travel in lane(s) depending on traffic demand (typically AM/PM peaks).
timetable - A pre-programmed list of time of day and day of week control events (such as green maxima, plan changes and other items) controlling when these take place.
Toucan crossing - A stand-alone combined pedestrian/cyclist crossing.
TOPAS - Traffic Open Products and Specifications, the organisation now responsible for maintaining the 25XX series of traffic product specifications and for Registering products as being compliant with them. Purchasers may require products which they purchase to be compliant with these specifications as an aid to ensuring product performance and compatibility.
Traffic Control Equipment – Any equipment used in connection with the control of traffic.
Traffic Management Systems – Systems used to control and manage Traffic Control Equipment, may be part of a UTC/UTMC system or standalone.
Traffic Signal Controller (TSC) – Equipment usually within a roadside cabinet, primarily to control traffic signals and also to interface with other traffic management sub-systems, including local infrastructure such as detection devices and remote systems including UTC.
Traffic Signal Engineer - A person with specialist skills, knowledge and experience for the design and commissioning of traffic signalling equipment.
tram signal - A signal which controls Light Rail Transit Vehicles running on-street at signalled junctions.
Transport for London (TfL) – Integrated transport authority for London.
TRANSYT - TRAffic Network StudY Tool, an off-line program for predicting the performance of a network of traffic signals with a given set of traffic flows and signal timings. In conjunction with its in-built optimiser, it is used to calculate the optimum set of timings for a given set of traffic flows.
TRL - Transport Research Laboratory.
uncontrolled crossing – Pedestrian crossings where users do not have precedence over vehicular traffic.
UTC - Urban Traffic Control, a system for the central control of electronic traffic control devices in a defined area, which will usually comprise primarily, but not necessarily exclusively, traffic signal installations.
UTC mode - A method of control available in a TSC where reception of control bits governs which stages operate when.
UTMC – Urban Traffic Management and Control, an open standard working with UTC systems to widely populate and disseminate a database between diverse sub-system platforms.
variable maximum green - A feature of vehicle actuated control which allows the maximum green timing to be varied according to traffic flow.
Variable Message Sign (VMS) – Equipment capable of showing a sign face or legend as prescribed in TSRGD or a blank grey or blank black face.
vehicle actuation mode – A method of control available in a TSC using detection to service demand in a cyclic fashion dependent upon current vehicle and pedestrian presence. The duration of the phase and stage appearances will vary in relation to traffic.
Visor - A device mounted above a signal aspect to prevent incident light falling on the lens and reducing contrast and/or to prevent the aspect being seen by road users for whom it was not intended (also hood).
vulnerable users – A general reference to Non-Motorised Users and those with mobility or sensory impairments in particular.
walk with traffic - A control system where pedestrian phases run with non-conflicting vehicle phases.
warden control – An optional feature of traffic signal controllers to allow school crossing patrol wardens a degree of control over the operation of traffic signals.
Webster and Cobbe - A method of calculating traffic signal timings developed by F V Webster and published in ‘Traffic Signals’ (RRL Technical Paper 56 by F V Webster and B M Cobbe) 1966.
wig wag - A signal having two similar aspects which are illuminated alternately.
Y - The sum of the y values of the critical traffic stream of each stage for all the stages in the cycle.
y value - The ratio of demand and saturation flow for a traffic stream.
Zebra crossing – A style of unsignalised controlled pedestrian crossing, typified by alternating black and white road markings and flashing yellow globes.