signal, terms and definitions · all red interval the display of red indications for all entering...
TRANSCRIPT
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Signal, Terms and Definitions
Last modified October 2, 2002, MVT
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A
AASHTO American Association of State Highway and Transportation
Officials.
Access Time The time interval between the instant at which data is called for
from a storage device and the instant at which delivery of the data
is completed.
Accessible Pedestrian
Signal
A device that communicates information about pedestrian timing
in non-visual format such as audible tones, verbal messages,
and/or vibrating surfaces.
ACIA Asynchronous Communication Interface Adapter; port through
which the 170 or IBM computer communicates to the outside
world.
Active Grade Crossing
Warning System
The flashing light signals, with or without warning gates, together
with the necessary control equipment used to inform road users of
the approach or presence of trains at highway railroad crossings.
Actuate To provide a signal or impulse to a controller input which is
intended to cause an event or sequence of events. Signal
origination is from a separate source such as a detector,
coordination device or a manual control.
Actuated Identifies type of control which responds to calling signals
generated by action of vehicles or pedestrian. (See Semi-Actuated
and Full-Actuated.)
Actuated Controller See Full Actuated
Actuation The operation of any type of detector, vehicle or pedestrian.
Operation implies the use of any output from a detector to the
controller to request right-of-way.
Adaptive Split Control A means of local intersection split selection based on vehicular
activity.
Add / Act (170's) The amount of time added to the added initial time for every
actuation. Added initial time is reset when entering a yellow
condition. Added initial time times concurrently with min initial.
Added Initial Portion An increment of time added to the minimum initial portion in
response to vehicle actuations.
Added Initial (Sec./Act.) The amount of additional time allotted to the minimum green for
each vehicle detected on an approach to the traffic signal. This
time is accumulated during the red time of the movement.
Address The identification of specific intersections for transmission of
commands or the receipt of data.
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Adjustable Signal A signal head having the signal faces mounted in the support
hardware so that each face may be adjusted or “aimed”, as
required, to present the indication to approaching traffic.
Advance (170's) Whenever C1-pin 80 goes from false to true the controller will
automatically advance phase timing to the next interval. Flashing
Don’t Walk, Yellow, and Red Clearance are not affected by the
advance input and will time and advance regardless of the
advance input.
Advance Actuated
Controller
An actuated controller that can count vehicles beyond the first. It
generally has variable initial interval actuation.
Advance Call Detector A detector located a considerable distance ahead of an
intersection (150 - 200 feet) which calls the green to that
approach and is no longer effective upon reaching the stop line
detector.
Advance Enable (170's) Whenever C1-pin 53 is true, a min recall will be placed on all
phases and a ped recall will be placed on the assigned ped phases.
Also a hold will be applied to all phases.
Advance Signal A discrete command issued by the master computer which causes
an online controlled unit to change condition, generally advancing
the unit to the next position or state.
Advance Walk Upon initial entry into a phase which is active for advance walk
and there is a ped call present, a walk will be displayed while the
phase is held red. Once the walk has timed, the phase will go
green. The phase is considered on once the walk is turned on so
even if preempted with just the walk on the phase will still go
green and time it’s min. Normal walk time is started after advance
walk times out. Time for the advance walk is taken from the Walk
2 setting for that phase. (W4IKS)
Advance Warning A per movement output used to give advance notice of an
upcoming yellow or red indication. Typically used at hidden
intersections with “prepare to stop” indicators.
Advisory Detection The detection of vehicles on one or more intersection approaches
solely for the purpose of modifying the phase sequence and or
length for other approaches to the intersection.
Algorithm A procedure, process, or rule for the solution of a problem. An
algorithm may be a set of computational rules for the solution of a
mathematically expressed problem.
All Red Interval The display of red indications for all entering vehicular traffic.
Alternate Coordination method whereby successive signal indications along
an artery do not give the same indication at the same time. Single
double and occasionally triple alternates are set up. Typically
used in urban grid systems.
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Alternating Current (AC) A current which reverses direction at regular intervals. The rate of
reversal is expressed in hertz (cycles per second).
American Wire Gauge
(AWG)
The standard measurement of wire size. It is based on the circular
mil system. 1 Mil equals .001.
Ampere The unit expressing the rate of flow of an electrical current. One
ampere is the current flowing through one ohm resistance with
one volt pressure.
Amplifier A solid state device used in a vehicle detection system that
produces a signal when a vehicle passes through or remains
within the detection zone of a sensing element.
Amplifier (Detector) An electrical device used to sense electrical load changes on
associated sensing equipment (e.g. inductive loops) and provide
an output to an intersection controller for vehicle detection.
Amplifier Oscillator A voltage controlled multi-vibrator (oscillator) that produces an
output frequency that varies as a function of the inductance and
capacitance of the sensing element and lead in combination.
Amplitude Modulation A method of transmitting information by varying the strength of a
carrier waveform in accordance with the instantaneous value of
the intelligence bearing signal.
Analog Timing Pertaining to a method of timing that measures continuous
variables, such as voltage or current, rather than digital numbers.
ANSI American National Standards Institute.
Antenna The radiating or receiving elements utilized in transmitting or
receiving electromagnetic waves.
API Application Programming Interface.
Approach All lanes of traffic moving towards an intersection or a mid-block
location from one direction, including any adjacent parking
lane(s).
Approach Monitoring The concept of having every approach, to an intersection, on an
individual load switch so that the conflict monitor can monitor
each approach individually.
Approved Equal This term refers to a component offered by the contractor as equal
to the one specified by catalog number or brand name in these
specifications. A device or piece of equipment shall be accepted
as approved equal only if approved by the engineer.
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Area Detection The continuous detection of vehicles over a length of roadway
wherein the call of a vehicle in the detection area is intended to be
held for as long as the vehicle remains in the area of detection.
(Most detectors cannot hold the call indefinitely.) Frequently
referred to as large area detectors, long loop detectors, or
presence detectors. See Large Area Detector. See Zone of
Detection.
Arterial A main street generally considered to be a thoroughfare with
preferential right-of-way, usually with coordinated signals along
its length.
Arterial Priority Options
(APO)
Is a feature available in TRANSYT-7F program to maximize
arterial progression opportunity in the comparatively heavy
coordinated movements.
ASCII American Standard Code Information Interchange. A standard
code that assigns special bit patterns of data.
ASCOT Adaptive Signal Control Optimization Techniques. A software
package for traffic surveillance and control of signalized
intersections.
Assembler A computer program that prepares a machine language program
from a symbolic language program by substituting machine
language instructions for symbolic instructions.
Assembly Language A machine dependent symbolic language which must be
converted to machine language before it is usable on a computer.
ASTM The American Society for Testing and Materials.
Asynchronous Data
Transmission
A mode of data transmission by which the execution of the next
instruction or next event is initiated by a signal that is generated
upon completion of the previous command or event.
ATC Advanced Traffic Controller.
Attenuation Distortion Distortion of a transmitted signal caused by the nonuniform loss
or gain at different frequencies.
Attenuator An electronic circuit element which reduces the strength or
magnitude of a signal or action.
Auto Restart Integration of hardware logic and electrical circuitry with
software programming capabilities enabling a computer system to
be reactivated without operator intervention, following a power
failure.
Auto / Manual Switch A cabinet switch when operated, discontinues normal signal
operation and permits manual operation.
Automatic Reset A reset by means of which the offset or beginning of the green
indication is checked automatically and adjusted if necessary
once each time cycle.
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Auxiliary Equipment Separate devices used to add supplementary features to a
controller assembly.
Average In coordination, the offset and cycle length used during periods
other than peak demand.
Average Day A day representing traffic volumes normally and repeatedly found
at a location, typically a weekday when volumes are influenced
by entertainment or recreation.
B
Back Panel A part of the controller cabinet/housing where all the various
equipment connectors and field wiring are terminated. The load
switches, flash transfer relays and emergency flasher are also
plugged into the back panel.
Backplate A strip of thin material extending outward parallel to the signal
face on all sides of a signal housing to provide a suitable
background for improved visibility of the signal indications.
Balance Adjuster A device used in span wire mount applications to permit
alignment of the point of suspension with respect to the center of
gravity of the signal head so that the signal will hang vertically.
Ballast A component used with lamps to control the current and to
provide correct voltage for starting and sustaining operation.
Ballast Mounting Ballast may be mounted within the luminaire housing (integral);
mounted in a weatherproof container attached to or beside the
luminaire (contiguous); or mounted on the vertical support
members (remote).
Bandwidth 1.) The amount of green time available to a platoon of vehicles in
a progressive signal system. Also referred to as through band.
2.) A range of frequencies that a communications channel will
carry without excessive attenuation.
Bandwidth Weighting
Factors
Is a programming feature available in MAXBAND-86 and
PASSER IV programs to provide extra priority to selected links
or traffic movements.
Barricade A portable or fixed barrier having object markings, used to close
all or a portion of the right of way to vehicular traffic.
Barricade Warning Light A portable, power-operated, lens-directed, enclosed light used in
either the steady burn or flashing mode to mark obstructions or
hazards in construction and maintenance work areas.
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Barrier A barrier (compatibility line) is a reference point in the preferred
sequence of a dual ring controller unit at which both rings are
interlocked.
Two reference points or barriers assure there will be no
concurrent selection and timing of conflicting phases for traffic
movement in different rings. Both rings cross the barrier
simultaneously to select and time phases on the other side.
Barrier Line See Compatibility Line.
Base A fitting that connects a pole or cabinet to the foundation.
Basic Actuated Controller One that cannot count vehicles beyond the first. It does not have
variable initial interval.
Baud A unit for expressing the rate at which information is transmitted.
Baud Rate An effective rate of data transmission expressed in bit
repetitions/second.
Beacon A traffic signal of one or more faces consisting of one section
each and used for flashing operation.
Beacon Flasher A complete electrical mechanism for controlling the operation of
a flashing beacon, including all necessary auxiliary apparatus.
Beam Candlepower The intensity of a beam forming light source expressed in
candelas measured in a given direction expressed in degrees.
Beam Spread The angle between the two directions in the plane in which the
candlepower is equal to a stated percent (usually 10 percent) of
the maximum candlepower in the beam.
Bi-directional Detector A detector that is capable of being actuated by vehicles
proceeding in either of two directions and of indicating in which
of the directions the vehicles were moving.
Binary (1) A characteristic or property involving a selection or condition
in which there are two possibilities. Use of a binary system is
predicated on the supposition that a duality exists: that is, a thing,
state or condition is or is not. (2) A numbering system based on
two which only uses the digits 0 and 1.
Bit (1) An abbreviation for binary digit. (2) A single character in a
binary number. (3) A unit of that information capacity of a
storage device.
Bit Rate The speed at which bits are transmitted, usually expressed in bits
per second.
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BIU (Bus Interface Unit) Is a key component in a modern NEMA TS2 signal cabinet. The
BIU is responsible for converting all the (formerly hardwired)
inputs and outputs that need to be controlled and monitored by the
controller into reliable, high-speed data packets. These data
packets are transmitted to and received from the controller, with
appropriate protocol and error checking data at up to ten times per
second per BIU. The only link between the BIU and the controller
unit is the SDLC bus.
Blank Door See Section Blank Door.
Blinking (BND) NEMA
Conflict Monitor
This signal condition may exist under certain abnormal
circumstances such as: controller output malfunction (i.e. output
toggling, pin-wheeling, etc.); the output of a load switch is
intermittently shorting to ground; intermittent field wiring due to
corrosion, etc.
BND (Blinking-Noise-
Dimming) Error Detection
Feature of NEMA conflict monitors. This error detection
supplements the unique firmware sampling and digital filtering
method for the field input signals which is intended to provide
only limited noise immunity. This filtering method cannot
differentiate a signal that is: irregularly Blinking (flickering); or
has constant extraneous Noise; or is Dimmed invalidly under
cabinet controller firmware control. This is due in part to the large
time constants which may be associated with these irregular input
waveforms in comparison to the digital filtering time constant.
The BND error detection function is designed to recognize many
of these possible input waveforms and will place the conflict
monitor into a fault mode if the aforementioned signal conditions
exist for a pre-determined period of time.
Box Span A type of an intersection span wire layout.
Braced Type Mast Arm A semirigid mast arm which is braced in position.
Bracket Arm A signal bracket, for bracket mount applications, which
complements a tubular bracket arm but which is not of tubular
construction.
Bracket Mount A signal mounting arrangement where the signal head is mounted
approximately parallel to the vertical axis of the pole.
Bridge Structure, Traffic
Signal
The structural member which is suspended between two or more
supports.
Broad Band
Communications
A band of communication frequencies above 4000 Hertz, usually
transmitted over coaxial cables.
Buffer A device or system used to make two other devices or systems
compatible, in particular, (1) a device or routine that compensates
for differences in time of occurrence or rates of flow when data is
transmitted between devices, or (2) a circuit put between two
other circuits to prevent undesirable interactions.
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Bull Rings Large metal ring used in the corners of a box span or other span
wire configurations.
Burn-in Procedure
(LED’s)
The procedure by which a LED signal module is energized at an
ambient temperature for a specified time duration to cause any
early electronic component mortality failures to occur and to
detect any component reliability problems before the product is
shipped to the end user for installation.
Burning Position Physical positioning of the lamp in the traffic signal. Normally,
traffic signal lamps are used in horizontal burning positions.
Bus Priority Cycle by cycle timing of a traffic signal so that beginning and end
times of green may be shifted to minimize delay to approaching
buses. The normal sequence of signal displays is usually
maintained.
Byte A term used to indicate a number of consecutive binary digits that
are usually operated as a unit. Eight bits usually constitute a byte.
C
C1 (170's) Connector through which input and output functions of the 170
controller are performed.
C2 (170's) Acia connector on 170 controller.
C20 (170's) 2nd
Acia connector on 170 controller used to feed information to
and from an external computer while the C2 connector is
connected to local 170 controllers being monitored by the master
controller.
Cabinet An outdoor enclosure, dust-proof and weather-proof, for housing
the controller unit and associated equipment.
Cable A group of separately insulated wires wrapped together and
covered with an outer jacket.
Cable Entrance Adapter A mounting bracket of tubular construction which is used
between the span wire hanger and the signal brackets to provide
for passing control cable into the signal head.
Cad (170's) Call / Active Display on the front of the 170.
Call Vehicle or pedestrian. The result of a detector actuation. A signal
in the control indicating the presence of a vehicle or pedestrian
requesting right-of-way.
Call Loop A loop detector placed near or at the stop bar to place a call into
the traffic controller requesting right-of-way.
Call to Non-Actuated
(CNA)
An actuated controller feature whereby the associated phase will
always serve the walk plus pedestrian clearance time regardless of
detector inputs.
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Calling Detector A detector installed in a selected location to detect vehicles that
may not otherwise be detected, and whose output may be
modified by the controller unit. This traditionally has meant a
small area detector near the Stop Line, to detect vehicles entering
the roadway from a driveway during the red or yellow signal. The
detector is disconnected when the green signal is displayed so that
extensions of the green can only come from the appropriate
Extension Detector.
Calling Relay A detector relay which will allow a detector actuation to be
transferred to the controller only when certain signal displays are
occurring.
Camshaft A device consisting of a stack of programmed cams operated by a
drive motor for intermittent advancement in increments to cause
contacts to open or close, thus causing the required signals to be
energized.
Candela Unit of luminous intensity.
Candlelight Distribution
Curve
A curve plotted in graph form showing the variation of
candlepower measurements at various angles around a light
source or luminaire. The distance of any point from the center
represents the candlepower of the source in that direction.
Candlepower A measure of the luminous intensity of a light source. One
candlepower equals 12.566 lumen. Luminous intensity expressed
in candelas and specified as candlepower in a specific direction.
Capacitance That property of a system of conductors and dielectrics which
permits the storage of electricity separated charges when potential
differences exist between the conductors. Its value is expressed as
the ratio of an electric charge to a potential difference.
Capacity The maximum number of vehicles that can pass over a given
section of a lane or roadway, during a given time period, under
prevailing traffic conditions.
Card Rack Mounted
Detectors
See Rack Mounted Detectors.
Carrier Frequency A single frequency that is modulated by the lower frequency
signals being communicated or carried, each carrier frequency
provides an independent communications channel.
Carryover (extended)
Output
The ability of a detector to continue its output for a predetermined
length of time following an actuation.
Cathode Ray Tube (CRT) An electronic vacuum tube similar to a TV picture tube
containing a fluorescent screen on which information or patterns
may be displayed.
CCITT Consultative Committee for International Telephone and
Telegraph.
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CD Carrier Detect.
Center Line A line indicating the division of the roadway between traffic
moving in opposite directions.
Central Business District
(CBD)
The portion of a municipality in which the dominant land use is
for intense business activity.
Central Processing Unit
(CPU)
The hardware component of a computer system that contains the
circuits that control and perform the execution of instructions It
consists of the main core storage, arithmetic unit(s) and special
register groups. (also called MPU).
Centralized System A computer control system in which the master computer,
communication facilities, console, keyboard, and display
equipment are all situated at a single, central location. From this
center, the operating staff coordinates and controls traffic signals
and related traffic control functions throughout the area.
Chamfer Diagonal saw slots at the corners of square or rectangular loops to
reduce the angle of bend of the loop wires at the intersecting saw
slots.
Change Interval The yellow interval following the green signal indicating the
change to a conflicting phase.
Changeable Message Sign A sign on which the legend may be changed by the selective
energizing of lamps arranged in a pattern, by the use of a rotating
drum, or other methods.
Channel (1) Electronic circuitry which functions as a loop detector unit.
(2) A path of communication.
Channel(s) A term used to describe the input(s) to the conflict monitor.
Chassis Ground A safety ground installed in all metal housed electrical devices
that help prevent electrical shock to operator.
Check An output circuit that indicates the existence of an unanswered
call on an opposing phase. This circuit is not affected by ped or
phase omit.
Checksum A mathematical value determined by programmed memory. A
checksum error in an indication that one or more bits of
programmed memory have changed incorrectly.
Chromaticity The color of the light emitted by an LED signal module, specified
as x-y or x and y chromaticity coordinates on the chromaticity
diagram according to the 1931 Commission Internationale
d’Eclairage (CIE) standard observer and coordinated system.
CIP Communication Interface Protocal.
Circuit A closed path followed by an electric current.
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Classification Detector A detector that has the capability of differentiating among types
of vehicles.
Clearance Interval(s) The interval(s) from the end of the right-of-way of one phase to
the beginning of an conflicting phase.
Clevis A “U” shaped piece of iron with holes for a pin, for attaching one
thing to another.
Clevis Pin The removable pin in a Clevis.
Closed Loop System A system in which the computer controls an external process
using information received from the process; e.g., the closed loop
in a traffic control system is from the computer to the controllers
and from the detectors to the computer.
Closed Network A network that contains closed loops.
Coded Status Bits The controller uses a three digit code indicating the status of one
ring. Various combinations of these outputs reflect the initial time
interval, extension interval, green rest state, yellow change
interval, red clearance interval, red rest state.
Coil A coiled conductor, wound on a form or core which uses electro
magnetic induction to cause changes in a current.
COM Communication (COMM)
Combined Master and
Secondary Controller
A secondary controller equipped with auxiliary contacts for
checking the offset and, when specified, means for accomplishing
other supervisory functions over all secondary controllers in the
system.
Communications Broad term used to denote the transmission of intelligence
between two or more points separated by some distance. May be
electrical impulses with specific identities or actual audible
signals.
Communication Links Cable and interface units which may include multiplexing
devices, to electrically interconnect all the various components in
the traffic signal control system, including the central computer,
the actuated controllers, arterial pre-timed controllers, and all
detectors. This term is used interchangeably with “interconnect”
or “interconnected facilities.”
Compatibility Line The dividing line crossing both rings, in dual ring operation, that
separates compatible phase combinations. Usually it divides
phases associated with North and South versus East and West.
Compensated Magnetic
Vehicle Detector
Any magnetic detector which is so designed and structured as not
to be affected by changing electromagnetic influence other than
those resulting from the passage of a vehicle. When properly
equipped, a compensated magnetic detector has substantial
directional characteristics.
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Compiler A computer program that translates high level language program
to symbolic language.
Computed Initial Portion An initial portion which is traffic adjusted.
Computer A device capable of accepting information, applying prescribed
processes to the information, and supplying the results of these
processes. It usually consists of input and output devices; storage,
arithmetic, and logic units; and a control unit.
Computer Program A series of instructions or statements in a form acceptable to the
computer which will achieve a certain result.
Concurrent Timing A mode of controller unit operation whereby a traffic phase can
be selected and timed simultaneously and independently with
another traffic phase.
Conditional Service A dual ring feature which allows re-service to an odd phase (left
turn) once the opposing through phase has gapped out. The
service is conditioned by the time remaining in the adjacent
through phase’s MAX time.
Conditioned Line A communications cable specially compensated to provide
improved transmission characteristics.
Conductance The measure of ability to conduct electricity.
Conductor A medium for transmitting electrical current. A conductor usually
consists of copper or other materials.
Conduit A metal or plastic tube for protecting electrical wires or cables.
Conduit Coupler A fitting that joins two separate pieces of conduit together.
Conduit LB A connecting fitting for conduit that provides access to the wire
running inside.
Condulet A fitting connected to solid or flexible electrical conduit to direct
the routing path and containing a removable cover for wire
pulling.
Conflict Monitor A device used to continually check for the presence of conflicting
signal indications or improper operating voltages and to provide
an output in response to the conflict or problem.
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Conflict Monitor Card This universal card provides the means to assign conflicting
proceed channels. It is designed to the NEMA Traffic Control
Systems Specifications (TS-1, part 6) and therefore is
interchangeable between other units complying with the NEMA
standard. The card is initially supplied with 66 empty wire jumper
locations. This permits all channels to conflict with all other
channels. To program a compatible channel, solder a wire jumper
into the appropriate location for that channel combination on the
program card. Make sure that any disconnected leads do not make
contact with any other lead on the card or the cabinet chassis
when the program card is inserted into the slot of the front panel.
Conflict Monitor Tester The device used to check the complete and proper operation of a
conflict monitor certifying compliance to NEMA standards.
Conflicting Call See Serviceable Conflicting Call.
Conflicting Phases Two or more traffic phases which cause interfering traffic
movements if operated concurrently.
Congestion Detection A system of hardware and software designed and operated to
provide data on the level of traffic congestion in the area being
detected.
Contact, Signal Circuit A device arranged to energize or de-energize signal light circuits
during specified interval.
Continuous Presence
Mode
A mode in which the detector output continues if any vehicle
(first or last remaining) remains in the field of influence.
Contoured Visor See Cutaway Visor.
Control Area A grouping of subareas. (A subarea is the smallest grouping of
intersections that the computer considers. These intersections are
so interdependent or close together that they always work in
consort.) Control areas are generally defined by the physical
proximity of subareas and by the similarity of traffic conditions
which permits independent control by the computer within the
constraints imposed by required interface between subareas and
overall system requirements.
Control Circuit The process of managing higher voltage circuits with lower
voltage devices.
Controlled Output The ability of a detector to produce a pulse that has a
predetermined duration regardless of the length of time a vehicle
is in the field of influence.
Controller (1) (Traffic) A device that controls the sequence and duration of
indications displayed by traffic signals; (2) (computer) under
computer supervision, a device that switches the signal circuits
according to the computer’s instructions.
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Controller Assembly A complete mechanism mounted in a cabinet for controlling the
operation of a traffic control signal.
Controller Cabinet The metal box that is installed near the intersection that contains
the electronic equipment and field wiring for operating a traffic
signal. Also called the controller housing.
Controller Housing see Controller Cabinet.
Controller Housing
Detector Panel
A termination point, located inside the controller cabinet/housing,
where loop detector field wiring is terminated.
Controller Interface Unit The piece of equipment inserted between the local intersection
communication terminal and the intersection controller to
translate the instructions from the computer into commands that
are recognized and responded to by the controller.
Controller Module Normally is a unit that is plug or jack connected to the internal
wiring of the controller and associated with a particular phase or
function.
Controller Unit A controller unit is that portion of a controller assembly that is
devoted to the selection and timing of signal displays. Sometimes
called a Dispatcher or Timer.
Controller Voltage
Monitor (CVM)
An open collector output maintained low by the controller as long
as the internally generated operating voltages are within
tolerances. Used by the conflict monitor to place the intersection
in flash should voltages fail.
Coordination The establishment of a definite timing relationship between
adjacent traffic signals.
The broad term applied to the interconnection controls in a
manner which allows vehicles to traverse the roadway without
encountering delay due to signalization.
Coordination Bandwidth This is a term use to describe the green time in a coordination
system. See Bandwidth
Coordination Offset Time relationship expressed in seconds or percent of cycle length,
determined by the difference between a defined interval portion
of the coordinated phase green and a system reference point. See
Offset.
Coordinator A device used to relate the timing of one controller unit to others
in a traffic signal system.
CRC Cyclic Redundancy Check.
Critical Intersection A selected, heavily traveled intersection within a coordinated
arterial. This intersection would be employed to dynamically
control the split at selected signalized intersections within the
arterial, base on vehicle detector input.
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Critical Intersection
Control (CIC)
An algorithm employed in traffic systems to dynamically control
the split at signalized locations where the traffic patterns are such
that special control, responsive to changing conditions, is needed.
Control strategies for such intersections require input from
detectors on each approach so that the split may be varied cycle to
cycle.
Critical Lane Detection A system of hardware and software designed to provide data on
traffic flow for a selected lane, usually the heaviest volume lane
on an approach to a signalized intersection.
Crossover Point The level of lane occupancy wherein the command function
changes from one cycle length to another, or from one offset
classification to another.
Crosstalk The adverse interaction of any channel of a detector unit with any
other detector channel in that unit or another unit. It is the mutual
coupling of magnetic fields that produces an interaction between
two or more detector units in the same cabinet when the units are
operating at similar frequencies. Crosstalk results in a detector
outputting an actuation in the absence of a vehicle.
Crosswalk (a) That part of a roadway at an intersection included within the
connections of the lateral lines of the sidewalks on opposite sides
of the highway measured from the curbs or, in the absence of
curbs, from the edges of the traversable roadway. (B) Any portion
of a roadway, at an intersection or elsewhere, distinctly indicated
for pedestrian crossing by lines or other markings on the surface.
Crystal (1) A semiconductor material whose atomic arrangement is in the
form of a crystal structure. Crystals are grown in a furnace by
immersing a properly orientated “seed” crystal into molten semi-
conductor material and slowly withdrawing during a rotation
process. Semi-conductor atoms adhere to the withdrawing seed,
forming a single crystal ingot. (2) A crystalline material used in
electronics as a frequency determining element or for
rectification.
CTS Clear to Send.
Curb A vertical or sloping member generally along and defining the
edge of a roadway.
Cutaway Visor A visor which encircles approximately 300 degrees around the
lens, the lower half of which may be cut away and contoured.
Cutoff The point on a roadway at which signal veiling becomes
effective.
Cycle The total time required to complete one sequence of signalization
around an intersection. In basic pre-timed control the cycle length
is fixed; in actuation the cycle length varies (up to predetermined
maximums) according to the number of vehicles involved.
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Cycle Length The time required for one complete sequence of signal indications
in seconds.
Cycle Locking When cycle lengths of approximately the same length are selected
by the computer for two or more adjacent sections of the system
network, one consistent cycle length is selected and imposed on
these sections. The sections are then, in effect, locked together on
the same cycle length.
Cycle Selection The process by which cycle lengths are chosen or calculated by
the computer to be imposed on the individual sections within the
network.
Cycle Selection Switch A device which when operated discontinues automatic selection
of cycle unit with associated split(s) and offset(s), and permits
manual selection of another cycle unit.
Cycle Zero Point See Time Reference Point.
D
Dark Mode The lack of all signal indications at a signalized location. (The
dark mode is most commonly associated with power failures,
ramp meters, beacons, and some movable bridge signals.)
Dark Signal An intersection without any indications displayed on the signal
heads. Usually caused by a power failure. According to Ohio
State law it is to be treated as a four (4) way stop.
Data Base The assemblage of data constants and parameters used by a
computer algorithm in the execution of the traffic control
function. Normally included are timing parameters, adjustment
coefficients, algorithm coefficients, and limit parameters.
DBM A measure of power in decibels referenced to one milliwatt.
DBRN (Decibel Random
Noise)
A measurement of noise power in decibels.
DCD Data Carrier Detect.
DC Keying The process of pulsing with DC a particular remote device or
apparatus.
Decoder A mechanism for translating a code into its various components.
Dedicated Lines Communication lines used solely to interconnect two or more
locations and not normally switched.
Delay (1) A measure of time that elapsed between the stimulus and the
response; (2) the retardation of the flow of information in a
channel for a definite period of time; (3) traffic delay, the time
lost by vehicle(s) due to traffic friction or control devices.
Page -18-
Delayed Call Detector A detector that does not issue an output until the detection zone
has been occupied for a period of time that has been set into the
appropriate detector unit.
Delay Inhibit A function of a delay/extend loop detector. This function
overrides the delay call function when the corresponding phase
green is on.
Delayed Output The ability of a detector to delay its output for a predetermined
length of time following an actuation.
Delineator A light reflecting device mounted at the side of the roadway, in
series with others, to indicate the alignment of the roadway.
Delta Clock The timing mechanism used to measure the elapsed time between
two events.
Delta L The change in inductance.
Demand The need for service, for example, the number of vehicles
desiring to use a given segment of roadway during a specified
unit of time.
Demand Controller See Occupancy Controller Assembly.
Demand Operation A mode of operation in which the service provided at an
intersection reflects the presence of demand for that service often
without regard for background cycling.
Density (1) (Traffic) A measure of the concentration of vehicles, stated as
the number of vehicles per mile (space density). Density =
Volume / Speed (point density). (2) (computer) the number of
bits that can be recorded per inch of magnetic tape.
Density Controller Actuated controller that has timing adjustments for the selection
of the allowable gap independent of the passage time. A volume-
density controller and modified density controller are each a type
of density controller.
Design Speed The speed used as typical by the designer of the detector /
controller scheme, under free traffic flow conditions.
Detection The process used to identify the presence or passage of a vehicle
at a specific point or to identify the presence of one or more
vehicles in a specific area.
Detection Zone The area of the roadway within which a vehicle will be detected
by a vehicle detector.
Detect-o-Duct A type of wire designed for the installation of embedded
inductance loop detectors. The conductor is inside a sleeve for
protection against cuts and nicks.
Page -19-
Detector A device for indicating the presence or passage of vehicles or
pedestrians. This general term is usually supplemented with a
modifier indicating type (e.g., loop detector, magnetic detector,
etc.), operation (e.g., point detector, presence detector, etc.), or
function (e.g., calling detector, extension detector, etc.).
Detector Amplifier A device that is capable of intensifying the electrical energy
produced by a sensor. An example is a magnetic detector
amplifier. A loop detector unit is commonly called an amplifier,
although its electronic function actually is different. See
Amplifier.
Detector Failures The occurrence of detector malfunctions, such as non-operation,
chattering, or other intermittent erroneous signaling as well as
occupancy errors and false alarms.
Detector Memory (ON) The retention of an actuation until the corresponding phase(s) is
serviced. The phrase might better be detection memory to make it
clearer that the memory is within the controller, not the detector.
Detector Mode A term used to describe the operation of a detector channel output
when a presence detection occurs. See Pulse Mode, Controlled
Output, Continuous Presence Mode, Limited Presence Mode.
Detector Panel The termination point for field loop detector wires entering the
housing. See Controller Housing Detector Panel.
Detector Setback Longitudinal distance between stop line and detector.
Detector Switching A control circuit that enables one detector's call to be transferred
to another controller phase.
Detector System The complete sensing and indicating group consisting of the
detector unit in the controller, the lead-in cable, the lead-in wires,
and the sensor.
Detector Unit The portion of a detector system other than the sensor and lead in
cable, consisting of an electronic assembly.
Diagnostics A program that facilitates computer maintenance by detection and
isolation of malfunctions or mistakes.
Diagonal Span A type of intersection span wire layout.
Dial Disconnect The process of interrupting the connection between the dial
pulsing circuit and the signal cam shaft rotational device in some
types of intersection controllers.
Dial Supervision The technique for allowing the dial to dwell for an adjustable
period of time in one or more of the phases comprising the cycle.
This permits the computer to independently extend the duration of
each phase beyond its preset minimum.
Page -20-
Dial Unit The rotating, calibrated dial mechanism on a controller equipped
with adjusting pins or keys and contacts to establish and divide
the time cycle in percent of cycle length for the required number
of intervals. The dial unit may also include pins or keys and
contacts to perform interlocking of the dial unit in step with the
cam unit and/or pins or keys and contacts to provide offset.
Generally referenced to a pre-timed type of control. Consists of a
dial with graduations in one percent increments 0 to 100. The
scale graduations are matched with physical locations of switch
actuations or initiate signals used in sequencing signalization.
Dielectric Any insulating material that is a nonconductor of electricity.
Digital Controller Unit A controller unit wherein timing is based upon a defined
frequency source such as 60 hertz alternating current.
Digital Timing Pertaining to a method of timing that operates by counting
discrete units usually based on the frequency of the power source.
Dilemma Zone A distance of time interval related to the onset of the yellow
interval. That portion of the roadway within which a driver is
indecisive regarding stopping prior to the stop line or proceeding
into or through the intersection. It is sometimes expressed as the
increment of time corresponding to the dilemma zone distance.
Dilemma Zone Protection Any method attempted to control the end of green interval so that
the vehicle will be avoided in the dilemma zone when the signal
turns yellow.
Dimming This feature allows selected signal indications to be dimmed
during night time operation.
Dimming (BND) NEMA
Conflict Monitor
The sampling and filtering algorithm allows ONLY half wave
(positive or negative) suppressed dimming. Other dimming
waveforms may be achieved under cabinet controller firmware
control and will be detected as a BND error within approximately
30 periods of the input waveform.
Diode A two element device, i.e., P-N junction, capable of rectification
by permitting current flow in one direction only.
Direct Current (DC) An electrical current which travels uniformly in one direction.
Direct Wire A communications medium that utilizes hard wire interconnect
between the transmission and reception points. See Dedicated
Lines.
Directional Detector A detector that is capable of being actuated only by vehicles
proceeding in one specified direction.
Directional Motion Loop
Detector
An induction loop detector consisting of two separate loops either
closely spaced or partially overlapping which is not affected by
the passage of a vehicle except in the desired direction.
Page -21-
Disconnect Hanger A mounting device for a span wire or a mast arm mount that
contains a terminal block for a plug and socket and a means of
readily attaching or detaching the signal head to and from the
hanger.
Disconnect Switch See Power Line Switch.
Disconnect Switch
Enclosure
The metal box that encloses the power line switch.
Disk Operating System
(DOS)
An organized collection of techniques and procedures for
operating a disk drive based computer system. This can be part of
a software package designed to perform input / output procedures,
sort, data conversion, or test, to name a few.
Dispatcher See Controller Unit.
Distributed System A control system in which individual computers are installed in
each of the major control areas of a total system and supervising
master is used to provide interface between the individual areas
and to make decisions on timing patterns effecting two or more
areas.
Divided Highway A highway with separate roadways for traffic in opposite
directions.
DMJM Daniel, Mann, Johnson, and Mendenhall
Double Entry See Dual Entry
DOW Day of week.
Down Time The time during which a device is unavailable for normal
operation.
Down Time Accumulator A clocking mechanism activated during the interval when a
device is inoperable. It provides a measure of the cumulative total
elapsed downtime.
Downstream The roadway movement at an intersection which extends from the
stop line, across the intersection and beyond in the through
movement.
Drift Changes in the electrical properties of the detector system or a
portion of it due to environmental changes particularly
temperature variations and rain water.
Drip Loop A turn of cable at an entrance fitting installed to prevent drops of
water entering the fitting.
Drop Procedures (1) The orderly processes or operations to remove a controller
from the supervision of the computer to standby mode. (2) The
process followed at the local intersection when a communications
failure occurs.
DTR Data Terminal Ready.
Page -22-
Dual Entry A mode of operation (dual ring) in which one phase in each ring
must be in service. If a call does not exist in a ring when it crosses
the barrier, a phase is selected in that ring to be activated by the
controller in a predetermined manner.
Dual Indication
Monitoring
This monitor function detects simultaneous indications of active
Green, Yellow, Walk, or Red field signal outputs on the same
channel. A dual indication fault, if enabled, places the conflict
monitor into a trip mode putting the signal on flash.
Dual Ring Controller Unit A controller unit containing two interlocking rings which are
arranged to time in a preferred sequence and to allow concurrent
timing of both rings, subject to the restraint of the compatibility
line (barrier).
Dummy Interval A redundant interval in the cam switching mechanism
incorporated so as to allow the total number of intervals in the
cycle to correspond integrally with the total number of intervals
provided on the cam switching mechanism.
Dummy Load An electronic device used to red out a conflict monitor channel on
the field wiring side of a load switch.
Duplex Two-way communication over a single communication link. See
Half Duplex; Full Duplex.
Duty Cycle The amount of time during a specified time period that an LED
signal module is energized, expressed as a percent of the specified
time period.
Dwell Interval The period of time in which a controller may stop to re-
synchronize with a master controller or rest until receipt of a
traffic actuation. Also see Rest.
Dynamic Detector See Passage Detector.
Dynamic Split Generation The process or computer program used to vary the split among
the various phases of a cycle in real time in accordance with the
conditions to be satisfied.
E
Echo Distortion The distortion caused by an impedance mismatch or by a sudden
change in the properties of a line which results in an echo or
reflected wave which lowers the quality of the transmitted signal
by distorting the shape of the wave.
Edge Line A line which indicates the edge of the roadway.
EEPROM See Electrically Erasable Programmable Read Only Memory.
Effective Loop Area See Zone of Detection.
Page -23-
EIA-RS232 Interface Standard interface between data terminal equipment and data
communication equipment employing serial binary data
interchange.
Electrically Erasable
Programmable Read Only
Memory (EEPROM)
A device which stores data that can be altered by computer
instructions. EEPROM’s can be erased and programmed without
special physical processes.
Electro/Mechanical Refers to equipment which performs its function on the basis that
an electrical impulse causes a mechanical action to take place. No
electron tubes or significant solid-state devices are used.
Electro-mechanical
Device
A device which is characterized by electrical circuits utilizing
relays, step switches, motors, etc.
Electro-mechanical
Electronic Controller
A controller combining electro-mechanical components and
electronic timing circuits comprised of vacuum electronic tubes,
resistors, capacitors and inductors, etc.
Electronic Generally applied to equipment using electron tubes and or solid-
state devices. This catalog separates the two with electronic
specifically assigned to electron tube equipment only.
Electronic Device A device which is characterized by electrical circuits utilizing
vacuum tubes, resistors, capacitors, inductors and which may
include electro-mechanical and solid state devices.
Elevator Mast Arm Mount A mast arm mount where the signal face is supported on the mast
arm by a bracket between the face sections so as to place one or
more of the sections above the mast arm.
Emergency Vehicle
Preemption
The transfer of the normal control of signals to a special control
mode for emergency vehicles.
Enable The turning on of a function in a controller, loop detector, or
conflict monitor.
Encapsulation The process of filling the saw slot with sealant to surround the
wires in the slot and protect them from traffic, weather, etc.
Encasement The loop wire is encased in a polyvinyl or polyethylene tube to
provide protection for the wire. Often referred to as Detect-a-duct
or other similar commercial names.
Encoder A device which converts data into a form for transmission over
the communication link between two points in a system.
Enhanced Pedestrian A CNA-1 (call to non-actuated) related feature whereby the walk
time will be equal to the MAX 1 value.
Epoxy A resin used in bonding.
Equipment Status
Monitoring
The ability to determine the operational characteristics of a
remote device in terms of “operating normally,” “malfunction,”
“communications errors,” etc.
Page -24-
EV Emergency Vehicle
Exception Days A traffic pattern timing routine stored in controller memory which
is activated to compensate for unusual traffic flow caused by a
special event (such as a sporting event).
Exclusive Pedestrian
Phase
A traffic phase allocated to pedestrian traffic only, provides a
right-of-way pedestrian indication to the exclusion of all
vehicular phases (all red).
Exclusive Phase Service Selected phases will be serviced sequentially, regardless of dual
entry. Phases not programmed for exclusive service will function
normally.
Expansible Controller A controller with the capacity built in to accept additional
features later in the field.
Extended Call Detector A detector with carryover output. It holds or stretches the call of a
vehicle for a period of seconds that has been set on an adjustable
timer incorporated into the detector. It can be designed to begin
the timing of that period when the vehicle enters the detection
area, or when it leaves. The latter is specified by NEMA. Also
referred to as a “Stretch Detector.”
Extendible Recall A form of recall whereby the associated phase will always serve
MIN green and further green time is subject to detector extension.
Extension (Green) The part of the green interval following the initial portion.
Extensions are based on vehicle actuations.
Extension Detector A detector arranged to register actuations at the controller only
during the green interval for that approach so as to extend the
green time of the actuating vehicles.
Extension Limit The maximum time of the extensible portion for which actuations
on any traffic phase may retain the right-of-way after actuation on
an opposing traffic phase.
Extension, Unit The timing interval during the extensible portion which is
resettable by each detector actuation. The green right-of-way of
the phase may terminate on expiration of the unit extension time.
External Minimum Recall Input, to all vehicle phases, to place a recurring demand on all
vehicle phases for a minimum vehicle service.
External Start This input when activated causes the controller unit to revert to its
programmed initialization phase and interval immediately upon
application of logic ground to the input. However, the controller
unit will not commence timing the selected interval until the input
is de-activated.
External Voltage The controller shall supply a regulated +24 volts DC for external
use.
F
Page -25-
Fail Safe A type of output relay design that produces a constant call,
thereby keeping traffic moving, in the event that the detector unit
fails.
A primary safety consideration in equipment and system design.
Precludes dangerous signalization when power or equipment
malfunctions occur.
False Call The actuation of a loop detector without the real presents of a
vehicle or pedestrian call.
Farad A unit of capacitance, usually expressed in microfarads, (uF) one
millionth of a farad.
Feedback A system or circuit path which is provided to verify or limit the
response to a command. Provides an indication that a command
has been executed properly.
Feeder Cable See Lead In Cable.
Field Connections This term refers to the termination point inside a controller
housing/cabinet where external components are wired.
Field of Influence See Zone of Detection.
Field Terminals Devices for connecting wires entering the controller assembly.
Field Wiring Any cables/wires that are used inside the controller housing to
connect the internal electronic equipment of the controller
housing to the various devices outside at the traffic signal
intersection (i.e., signal heads and loop detectors).
Filament The electrical resistance element heated to incandescence by
electric current.
FIO Field Input/Output
Firmware Logic circuits in read only memory (ROM) that may be altered by
the software under certain circumstances.
Fixed Face Signal See Non-adjustable Signal.
Fixed Initial Portion A preset initial portion that does not change.
Fixed Time Controller See Pre-timed Controller.
Flash Green Causes the green to flash for each assigned phase whenever the
green for that phase is on. Defeats guaranteed yellow minimum.
(W4IKS)
Flash Switch A cabinet switch, when operated, discontinues normal operation
and causes the flashing of any predetermined combination of
signal lights.
Page -26-
Flash Terminals Special terminals in a controller so wired that by an interchange
of jumpers, flashing operation may be arranged to give either
yellow or red on the major or minor street.
Flash Transfer Relay A relay inside the controller housing/cabinet that is used to switch
the operational function of the cabinet from a stop and go to
flashing operation.
Flasher A device used to turn highway traffic signal indications on and
off at a repetitive rate of approximately once per second.
Flasher Controller
Assembly
A complete electrical mechanism for flashing a traffic signal or
beacon.
Flashing (Flashing Mode) A mode of operation in which a traffic signal indication is turned
on and off repetitively.
Flashing Beacon A section of a standard traffic signal head, or a similar type
device, having a yellow or red lens in each face, which is
illuminated by rapid intermittent flashes.
FL/DW Don’t Walk interval will flash after Walk has timed out. It cannot
be shortened by Emergency Vehicle preemption; however, it will
be cut short by Railroad preempt.
Flashing Feature A relay or other device installed in a controller which, when
energized from a remote point or by an automatic time switch,
discontinues normal signal operation and causes the flashing of
any predetermined combination of signal lights.
Flashing Logic Output The controller shall supply an output alternating between 0 volts
and +24 volts DC with a 1 second pulse rate and 50 +/- 2 percent
duty cycle. This output shall switch within 5 degrees of the zero
crossover point of the AC line.
Flexible Mast Arm Mount A mast arm mount where the signal head is attached to the mast
arm with a flexible joint and connector to permit “free swing”
between the signal and the mast arm.
Flexible Progressive
System
A signal system in which the intervals at any signalized
intersection may be independently adjusted to the traffic
requirements to give the maximum efficiency.
Flow Chart A graphical representation showing the interconnected sequential
logical steps required for the definition, analysis or solution of a
problem. Used to describe a process by displaying its functions in
the order and priority of flow.
Fluorescent Fixture A lighting unit containing a fluorescent lamp mounted within a
housing with a metal framed plastic cover and a reflector.
Focal Point The design point within the optical unit, related to the reflector,
from which emitted light will be redirected by the reflector into a
prescribed pattern.
Page -27-
Force-Off Activation of this signal, per ring, causes the controller to
terminate the green extension intervals for that phase. FORCE-
OFF will occur as long as there is an opposing call registered, the
phase in service is not in its initial period and the associated
pedestrian indication is not in WALK or PED-CLEARANCE.
Used in preemption and coordination.
Force Off Command A system command that forces the termination of a phase of a
traffic signal.
Foundation A poured concrete footing to support a pole or housing.
Free Operation A coordinated system that is running without coordinated control.
Freeway Surveillance Process or method of monitoring freeway traffic performance and
control system operation.
Frequency The number of times an alternating current repeats its cycle in 1
second.
Frequency Division
Multiplexing (FDM)
Involves the use of different frequencies (tones) to represent
different messages. On a typical telephone channel of voice grade
quality (Series 3000), up to 16 different tones representing 16
different messages can be transmitted.
Frequency Shift Keying
(FSK)
A form of digital frequency modulation employing discrete
frequencies for specific signals; e.g., marking signals. The
transmitter is changed from one frequency to another; i.e. keyed
to represent a different information character.
Full Actuated Identifies a type of intersection control with vehicle detector input
capability in all phases.
Full Actuated Controller
Assembly
A type of traffic actuated controller assembly in which means are
provided for traffic actuation on all approaches to the intersection.
Full Circle Tunnel Visor A visor which encircles the entire lens.
Full Duplex A communication facility providing simultaneous transmission
and reception.
Function Modular
Controllers
Controllers constructed so that additional functional capabilities
may be provided by the addition of hardware and or software
modules. A single module provides a function(s) for all phases in
the controller.
G
Gap The timing interval during the extensible portion which is
resettable by each detector actuation. The green right-of-way of
the phase may terminate on expiration of the unit extension time
(max time).
The time interval between the end of one vehicle detector
actuation and the beginning of the next actuation.
Page -28-
Gap, Maximum The maximum time on volume density timed controllers allotted
for vehicles to proceed through the intersection. The interval
portion is decreased to a fixed minimum in proportion to traffic
demands.
Gap, Minimum The lower limit to which the extendable portion or terminating
gap may be decreased on volume density timed controllers.
Gap Out Terminating of a green phase due to an excessive time interval
between the actuations of vehicles arriving on the green, so green
may be served to a competing phase.
Gap Reduction A feature whereby the “unit extension” or allowed time spacing
between successive vehicle actuations, on the phase displaying
the green in the extendable portion of the interval is reduced. See
TBR (Time before Reduction), TTR (Time To Reduce), and MIN
GAP.
Generation (First, Second,
Third)
Denotes the progression of the state-of-the-art in control
philosophies for computerized traffic signal systems.
First generation uses pre-stored timing program developed off-
line based on previously collected traffic data. Control plans can
be selected on the basis of time of day, operator selection, or
automatic matching of the timing program best suited for existing
traffic pattern conditions.
Second generation contains an on-line optimization routine to
develop the timing program in real time based upon current traffic
conditions. This process is repeated at 5 to 10 minute intervals
whenever changing traffic conditions justify computation of a
new set of control parameters.
Third generation deals with individual intersections on a cycle-
by-cycle basis using an area wide optimization criteria.
Glass Envelope The bulb is designated by prefix letter(s) and suffix number(s).
The prefix letter indicates the shape, while the suffix number
indicates the maximum diameter of the bulb, expressed in eights
of an inch (does not apply to PAR type lamps).
Global Variable A variable applying to the total system and used in all modules of
a program, thereby requiring only one memory storage location.
Gore The center area immediately past the point where two traffic ways
divide at an acute angle; usually where a ramp leaves a roadway.
GPS Global Positioning System.
Green Band The time in seconds elapsed between the passing of the first and
last possible vehicle in a group of vehicles moving in accordance
with the designed speed of a progressive traffic control system.
Page -29-
Green Extension System Hardware assembly of extended call detectors and auxiliary logic.
The logic can monitor the signal display, enable or disable the
extended call detectors, and hold the controller in artery green.
Green Interval (Right-Of-
Way)
The operation of a controller in causing traffic signals to display
indications permitting vehicles or pedestrians to proceed in a
lawful manner in preference to other vehicles or pedestrians.
Green Split A division of the cycle length allocated to each of the various
phases. Can be expressed for arterial progression.
Grid A group of coordination thoroughfares covering a large area with
movements in several directions. The entire area is controlled and
synchronizes movements to minimized delay. Master control
usually is centralized.
Ground The earth and all parts conductively connected to the earth.
Guaranteed Passage Time If programmed, a phase will commit-to-terminate due to reduced
gap-out but actual service will extend one full preset extension
interval to allow the last vehicle in a staggered platoon to pass
through the intersection.
GY-Dual Indication
Monitoring
This monitor function detects a simultaneous indication of active
Green and Yellow field signal outputs on the same channel. It is
used to monitor channels which have an unused Red field signal
output tied to AC+ (i.e. five section signal head). A GY-Dual
indication fault, if enabled, causes the signal to go into a flashing
operation.
H
Half Duplex A communication facility providing both transmission and
reception, but not simultaneously.
Hand Hole See Pull Box. Also a word use to describe the hole cut in the side
of a steel strain pole for access to the inside.
Hard Copy Data permanently recorded on paper, film or other tangible media
for later reference.
Hard Wire Interconnect A common type of coordination where wires are use to run
between intersections to synchronize the coordinated system.
Henry (h) The measure of inductance, defined as the inductance of a circuit
in which a counter electromotive force of one volt is generated
when the current is charging at the rate of one ampere per second.
Hertz (Hz) The modern term used as the unit of measure when expressing
alternating current potentials, formerly called cycles per second.
Hierarchal System A system having various levels of priority or preference.
Page -30-
Highway Traffic Signal Any power operated traffic control device (except a sign or a
barricade warning light or steady burning electric lamps) by
which traffic is warned or is directed to take some specific action.
Hold A command to the controller which causes a phase to dwell in
green when it is serviced. All the phase intervals will time
normally but will not cause the phase to terminate. Advancement
out of green is dependent upon the removal of the HOLD input or
activation of a higher priority signal such as Force-Off or Interval
Advance. If HOLD is activated for a phase it will rest in vehicle
green but its associated ped rest state depends on wether the phase
is actuated or not. For a phase called to non-actuated with
opposing demand, if HOLD is activated while the ped is in
WALK, the ped will rest in WALK until HOLD is released and it
will then enter ped clearance. If HOLD is activated while the ped
is in DON’T WALK it will rest there. For an actuated phase, the
ped service will cycle normally but rest finally in DON’T WALK.
The ped will recycle in response to demand as long as there are
no opposing calls registered.
Hold On Line A connection that modifies a controller from full actuated,
isolated operation to semi actuated, system controlled operation.
It is used as the basic tie from the local intersection to the system
master.
Hold Signal A signal to an intersection controller commanding it to retain the
specified phase (usually the coordinated phase) even in the
presence of conflicting demands.
Home Run Cable See Lead In Cable.
Honda 100 A small motorcycle commonly considered to be the smallest
registered motor vehicle. It is used as the baseline for motorized
vehicle detection.
Hood See Visor.
I
I.E.S. Illuminating Engineering Society.
Impulse Noise Voltage spikes which are impressed on a line or circuit as a result
of momentary voltage surges.
IMSA International Municipal Signal Association.
Inbound The traffic condition wherein an imbalance exists with heavier
flow towards central points. Also described as the A.M. peek
period.
Indication, Signal The illumination of a signal lens (or an equivalent device)
whereby the movement of vehicular or pedestrian traffic is
controlled.
Page -31-
Indicator Lamp Control Input to disable controller unit indicators. The controller unit
might not employ this input, (optional).
Indicator Lights Visual aids showing actuations and timing of intervals or phases
on a controller for the purpose of programming, inspection, and
maintenance.
Inductance The property of an electric circuit or of two neighboring circuits
whereby an electromotive force is generated in one circuit by a
change of current in itself or in the other. The ratio of the
electromotive force to the rate of change of the current. Measured
in micro henries(uh).
Inductive Reactance The reactance (ohms) of an ideal (lossless) inductor is the product
of the voltage across the inductor and the sine of the phase angle
(90 degrees) between inductor voltage and current divided by the
inductor current assuming sinusoidal operation.
Infrared Detector A detector that senses radiation in the infrared spectrum. With
infrared detectors the detection zone is illuminated with low
power infrared light. As vehicles pass in the detection zone, the
infrared light is reflected from vehicles and is focused by an
optical system onto a sensor matrix. A real time signal processing
technique analyzes the received signal and determines the
presence of a vehicle.
Infrared detectors are two types: Active and Passive. Active
infrared detectors are most applicable to stop line presence and
approach presence detection. Passive infrared detectors detect
moving vehicles only, normally up to 300 feet from the detector
unit.
Inhibit An action or signal which prevents a normal change in the
operating sequence of a control. Is used to obtain coordination or
other special condition upon command from an external source.
Inhibit Max Termination A signal on this input line disables the termination of any phases
in that ring due to the phases reaching their maximum time limits.
In the actuated mode, a phase will not terminate due to max out,
but still may gap out an service conflicting calls. In non-actuated
operation, this input will cause non-actuated phases to service
either the programmed pedestrian interval or the initial interval,
whichever is longer.
Initial Green See MIN Green.
Initial Portion The first timed portion of the green interval in an actuated
controller unit. See Fixed Initial Portion, Computed Initial
Portion, Maximum Initial Portion, Minimum Initial Portion,
Added Initial Portion.
Input / Output (I/O) A general term for equipment used to communicate with a
computer.
Page -32-
In-Roadway Lights A special type of highway traffic signal installed in the roadway
surface to warn road users that they are approaching a condition
on or adjacent to the roadway that might not be readily apparent
and might require the road user to slow down and/or come to a
stop.
Instruction Panel The face plate of a controller mechanism on which the adjustable
controls and their associated indications are mounted.
Integrated Circuit A combination of components that are processed at the same time
from common materials.
Interconnect The communication network usually consisting of electrical cable
connecting the system master with local control stations, for
example, intersection controllers.
Interconnected Controller A controller which operates traffic signals under the supervision
of a master controller.
Interconnection Refers to method of communication between distant points to
obtain coordinated control or other master control. May be direct
wire or telephone line.
Interface A relay or electronic device(s) which isolates and matches one
portion of a system to another. Assures that each major unit
receives impulses which exhibit the proper characteristics and
prevents undesirable interaction between units.
Interlock A feature of electro-mechanical controllers which maintains the
timing dial in step with the camshaft.
Interrupts A break in the normal flow of a system or routine such that the
flow can be resumed from that point at a later time.
Intersection The term applied to roadways that meet or cross.
The area embraced within the prolongation or connection of the
lateral curb lines, or, if none, then the lateral boundary lines of the
roadways, of two highways which join one another at, or
approximately at, right angles; or the area within which vehicles
traveling upon different highways joining at any other angle may
come in conflict.
Also, where a highway includes two roadways 30 feet or more
apart, then every crossing of each roadway of such divided
highway by an intersecting highway shall be regarded as a
separate intersection. In the event such intersecting highway also
includes two roadways 30 feet or more apart, then every crossing
of two roadways of such highway shall be regarded as a separate
intersection.
The junction of an alley or driveway with a roadway or highway
shall not constitute an intersection.
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Intersection Control
Beacon
A beacon used only at an intersection to control two or more
directions of traffic.
Intersection Status (1) The knowledge of whether a controlled intersection is “on-
line” or operating in its standby mode. (2) In some systems, the
knowledge of whether the intersection is displaying Main Street
Green or not. (3) In other systems, the knowledge of the specific
interval in which the cam shaft is positioned or the particular
phase being displayed.
Interval The time period allotted to a specific control function. Does not
result in a signal change but does indicate a transfer to control
within the unit to another circuit, i.e., Initial Interval, Extension
Interval, etc.
Interval Advance Causes the interval in service to terminate; (either vehicle green,
vehicle clearance, ped WALK or ped clearance). The interval will
attempt termination and sequencing normally, however,
advancing out of green will register a call for that phase.
INTERVAL ADVANCE will be effective when the signal is
released, to avoid continuous cycling if the signal is left activated.
Activation of this input will cause immediate termination of the
interval in process of timing.
Interval Sequence Specifies the order in which the various intervals are displayed.
A predetermined consecutive order of appearance of signal
indications during successive intervals within a time cycle. It may
also be referred to as the Color Sequence.
Interval Sequence Chart A chart designating the order in which the phases of a cycle occur
and the associated signal display for each interval.
Interval Timing The passage of time that occurs during an interval.
Island An area within a roadway in which vehicular traffic is excluded.
Isolated Controller
Assembly
A controller assembly for operating traffic signals not under
master supervision.
Isolated Intersection
Control
Form of signal control for a single signalized intersection through
which the flow of traffic is controlled without consideration of the
operation of adjacent signalized intersections.
Into and Out Off Flash This is a specified operation of NEMA. It requires the controller
to startup and shutdown, when the flash operation is called for, in
a proper sequence.
ITE The Institute of Transportation Engineers.
ITS Intelligent Transportation System
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IVHS Intelligent Vehicle Highway System.
J
Jack A receptacle in a controller cabinet in which a plug-in device may
be inserted.
Jack Box See Disconnect Hanger.
Jack Mounted Relay A relay equipped with a prong sub-base which may be removed
or replaced without disturbing any wiring.
Junction Box See Pull Box.
Junction Well See Pull Box.
K
Kilohertz (kHz) A Thousand hertz. A measure of frequency.
L
L The symbol used for inductance (also) The change in inductance.
Lamp The part of the optical unit which, when energized, electrically
provides the optical unit light source.
Lane A standard width of roadway of significant proportion to permit a
single vehicle safe passage.
Lane Line A line separating two lanes for traffic moving in the same
direction.
Lane Occupancy A computer value derived from detector input data which serves
to indicate the amount of street surface being utilized by vehicles
in a single traffic lane. It is expressed as a percentage of time a
detector is occupied over the total sampled time.
Lane Occupancy
Controller
See Occupancy Controller Assembly.
Lane Use Control Signal A highway traffic signal which is erected to control the direction
of vehicular traffic movement in an individual lane.
Lane Use Sign A sign indicating regulations governing use of specific lanes.
Large Area Detector A detector or series of detectors wired together in series or
series/parallel covering an area in the approach to an intersection.
Detection area varies from 6 x 40 ft. to 6 x 100 ft. or larger. One
of the more common configurations is four 6 x 6 ft. loops spaced
9 or 10 ft. apart for a length of 51 or 54 ft.
Lashing Rods Wire that is design to attach cables to the span wire.
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Last Car Passage A selected feature of a density controller which, upon gap-out,
will cause the green to complete the timing of the passage time.
The last vehicle to have been detected, known as the Last Car,
will therefore retain the green until it reaches the stop line. Thus,
it is assured of avoiding the dilemma zone problem and of
clearing the intersection. This feature is not defined by NEMA,
however, a number of manufacturers provide it.
Lead In Cable The electrical cable which served to connect the lead in wire to
the input of the loop detector unit. Sometimes called “home-run”
cable or transmission line.
Lead / Lag Operation A feature which makes it possible to reverse the phase sequence
on a phase pair basis. The phase pairs, 1 - 2, 3 - 4, 5 - 6, 7 - 8
when reversed, the odd phase will lag the even phase instead of
leading as is normal.
Lead In Wire (Loop Lead
In)
That portion of the loop wire between the physical edge of the
loop and the pull box which should be twisted a specified number
of turns per foot. For a magnetic detector and magnetometer it is
the wire which runs from the sensor (probe) to the pull box.
Lead Phases First phases timed after crossing a side barrier (provided there is a
demand).
LED Light Source A single light emitting diode (LED) or an array of LED’s
LED Signal Module An array of LEDs and lens that are capable of providing a signal
indication. An LED signal module shall be capable of replacing
the optical unit of an existing vehicle traffic signal section.
Lens The part of the optical unit through which light from the light
source and reflector passes and, in so doing, is redirected into a
prescribed pattern and is filtered to a prescribed color.
Light Center Length
(L.C.L.)
The dimension, in inches (cm), from the center of the filament to
the top of the base (including solder on the base eyelet).
Light Emitting Diode A solid state device that emits light when current flows. See LED.
Light Sensitive Detector A detector consisting of a light source and photoelectric cell or
cells, capable of being operated by the passage of a vehicle
interrupting the beam or beams of light. When properly equipped,
directional characteristics are present.
Light Stabilization
Procedure
The procedure by which an LED signal module is energized at a
given temperature for a specified time duration to cause
stabilization in light output.
Lightning Protection A circuit or device that suppress lightning when connect to earth
ground.
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Limit, Extension The maximum time of the extensible portion for which actuations
on any traffic phase may retain the right-of-way after actuation on
an opposing traffic phase.
Limit, Maximum The maximum green time after an opposing actuation, which may
start in the initial portion.
Limited Presence Mode Operation of a detector whereby output continues for a limited
period of time if vehicles remain in field of influence.
Limited Progression
System
A signal system in which the various signal faces controlling a
given street give “GO” indications in accordance with a time
schedule to permit (as nearly as possible) continuous operation of
groups of vehicles along the street at a planned rate of speed,
which may vary in different parts of the system.
Line Filter A circuit or device that suppress noise on the AC power line.
Link (1) (Computer) A process to gather or write two or more
separately written, assembled, or compiled programs or routines
into single operational entities. Some computer systems have
special programs called linkage editors to connect address
components into symbols or to perform relocation to avoid
overlapping; (2) (traffic) the length of roadway between two
signalized locations.
LIP See Local Intersection Program.
Load Relays Magnetically operated contacts energized from low amperage
controller circuits to switch higher amperage signal indication
circuits.
Load Switch A device used to switch power to the signal lamps.
Load Switch Drivers (Vehicle, Pedestrian and Overlap). Three outputs (each) per phase
are issued to the load switches indicating controller status.
Load Switch Tester A tester used to test load switches for malfunctions.
Loader A program that operates on input devices to transfer information
from off-line memory to on-line memory.
Loading Coil A coil of wire with turns laid adjacent to employ inductive
coupling effects to maximize the inductance of the coil. An iron
core is frequently used to increase the coupling. The resulting
inductance is used to compensate electronic circuits to improve
performance.
Local Controller See Controller.
Local Coordination Unit See Local Offset Unit.
Local Intersection
Program
A Type 170 software program developed by Caltrans which
incorporated detector timing features within the program.
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Local Offset Unit An auxiliary synchronous device applied to a non-synchronous
controller to cause the controller to keep in step with a control
frequency, which may be the AC power frequency. May have
multiple-offset capabilities.
Local Supervisory
Mechanism
See Local Offset Unit.
Local Variable A variable whose name is known only to the subprogram to
which it belongs. Also refers to a variable parameter which is
intersection specific.
Locking (Section or
Group)
A method of system control whereby one section (or sub-system)
selects the coordination pattern for one or more other sections.
Locking Detection
Memory
A selectable feature of the circuit design for a controller phase
whereby the call of the vehicle arriving on the red or yellow is
held by the controller after the vehicle leaves the detection area
until it has been satisfied by the display of a green interval to that
phase.
Logic Diagram A block chart showing the interrelationship of reason functions.
Logic Element The smallest building block in a computer that can be represented
by logical operation in an appropriate system of symbolic logic.
Logic Ground This connection shall be the reference ground for the input and
output and internal logic signals. This output must not be
connected to AC- (common) or Chassis Ground within the
controller unit.
Loop One or more turns of insulated wire installed to establish a zone
of influence to detect the presence or passage of vehicles when
used in conjunction with a loop amplifier.
Loop Detector A device capable of sensing a change in inductance of a loop
sensor imbedded in the roadway caused by the passage or
presence of a vehicle over the loop.
Loop Detector Unit An electronic device which is capable of energizing the sensor
loop(s), of monitoring the sensor loop(s) inductance, and of
responding to a predetermined decrease in inductance with an
output which indicates the passage or presence of vehicles in the
zone of detection. It is the electronics package, exclusive of the
loop(s) and lead in cable.
Loop Occupancy
Controller
A detector or controller design using long detection loops
(normally 30 ft or longer) and detector units operated in non-
locking mode. A loop occupancy controller may, but not
necessarily, be designed to rest in all red in the absence of any
traffic demand.
Loop System A combination of loop of wire connected through lead-in cable to
the detector input terminals.
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Louvered Visor A tunnel visor with inserted louvered device to cut off the signal’s
visibility from a direction where it is not desired to be seen.
LSI Chip An electrical component with more than 1,000 logic elements.
This is “Large Scale Integration” of miniature elements and is
used in some loop detector units of digital design.
Lumen Unit of luminous flux. Traffic signal lamp output is rated in
lumen’s. 12.566 lumen’s equal one candlepower.
Luminous Intensity The luminous flux per unit solid angle in a given direction,
expressed in Candelas (cd).
Luminous Intensity
Degradation, Long Term
The reduction in luminous intensity that normally occurs when an
LED is illuminated over an extended period of time.
M
Machine Language (1) A set of symbols, characters or signs, and the rules for
combining them, that conveys instructions or information to a
computer. (2) A language that can be directly interpreted by the
control section of the machine. (3) Information or data expressed
in code that can be read directly, used or written by the computer
or peripheral machines without further processing. See Assembly
Language, Compiler Language.
Magnetic Detector A detector that senses changes in the earth’s magnetic field that
are caused by the movement of a vehicle near its sensor. It is a
vehicle detector placed under the roadway which makes use of
both the earth’s magnetic field and the energy change created by
the passage of a vehicle over the detector to produce an output.
Magnetic Gradient
Vehicle Detector (MGVD)
A device which uses a magnetic principle to detect vehicles.
Magnetic Shadow The distortion of the flux lines of the earth’s magnetic field as
they pass through a ferrous vehicle, due to the fact that the vehicle
is more permeable to these flux lines than is air.
Magnetometer A device capable of being actuated by the magnetic disturbance
caused by the passage or presence of a vehicle. A magnetic flux
generator/sensor is installed in the roadway and connected to
sensor amplifier electronics.
Magnetometer Detector A detector that measures the difference in the level of the earth’s
magnetic forces caused by the passage or presence of a vehicle
near its sensor. It is a device capable of being activated by the
magnetic disturbance caused by the passage or presence of a
vehicle. A magnetic flux generator/sensor is installed in the
roadway and connected to sensor amplifier electronics.
Main Street Green (MSG) Data sent from the intersection controller to the central computer
indicating that the controller is displaying a green signal to the
main traffic phase (coordinated phase).
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Major Street or Major
Highway
The roadway approach or approaches at an intersection normally
carrying the major volume of vehicular traffic.
Malfunction Management
Unit
Same as Conflict Monitor.
Manual Control Enable Is used in conjunction with Interval Advance. When activated, it
stops the timing of all but clearance intervals, places vehicle and
pedestrian calls on all phases, requires two sequential activations
of Interval Advance to terminate a phase green, and inhibits the
effect of Interval Advance during clearance intervals. The first
actuation of Interval Advance during a phase green will cause the
vehicle phase to advance through its initial interval and the
concurrent ped service to enter flashing DON’T WALK. The
controller will then attempt to sequence normally. When
MANUAL CONTROL ENABLE signal is released, the controller
will time the interval it was in last completely.
Manual Intervention The ability of the system operator to manually select a specific
timing program or pattern.
Manual Operation The operation of a controller by means of a hand operated device;
i.e., police push button.
Manual Push Button An auxiliary device for hand operation of a controller.
Manual Reset A reset by which it is possible to manually establish the offset.
Refer to Offset Seeking Modes.
Map Display A device which graphically portrays the system of streets under
control. Indicator lights are placed at the signalized intersections
to display various information provided by the computer system.
Mast Arm A signal head mounting supported from a rigid arm extended over
the roadway for the purpose of supporting the signal head.
Mast Arm, Flexible Mount A mast arm mount where the signal head is attached to the mast
arm by a flexible joint and connector to permit “free swinging”
between the signal and the mast arm.
Mast Arm, Rigid Mount A mast arm mount where the signal head is rigidly affixed to the
mast arm to prevent any relative movement between the signal
and the arm.
Master A control device for supervising and monitoring a system of
secondary (local) controllers, maintaining definite time
interrelationships, and or accomplishing other supervisory
functions. In the case of traffic responsive operation, the master
generally includes computation equipment and recording
equipment.
Master Control Centrally located equipment designed to supervise a number of
intersections and used to select programs on secondary control
equipment to best suit traffic needs.
Page -40-
Master Controller
Assembly
A controller assembly for supervising a system of secondary
controllers, maintaining definite time interrelationship, selecting
among alternate available modes of operations or accomplishing
other supervisory functions.
Master Secondary
Controller Assembly
A controller assembly operating traffic signals and providing
supervision of other secondary controller assemblies.
Max Extension Normally the MAX 1 and MAX 2 green times and Time Before
Reduction will begin at the start of phase green. If MAX EXT is
programmed, they will begin at the end of the initial interval. This
will prevent any added initial time from reducing the extension
time and prevent max-out at the wrong time.
Max Recall This shall place a constant call for service on a phase(s) which
shall cause the phase(s) to be serviced each cycle for an interval
equal to the Maximum Green time programmed for that phase(s),
regardless of detector inputs.
Max 2 Selection It shall be possible to program two separate maximum green
times for each phase on the front panel of its respective Phase
Timing module. Normal controller operation shall use the time
designated Max 1. Activation of this control signal shall cause the
controller to use the Max 2 time setting.
Maximum Added Initial In density actuated operation this shall be the upper limit to which
the added initial may extend as a result of added initial time.
Maximum Green Two separate maximum green intervals shall be programmable.
Normal controller operation shall use the Max 1 time to
determine the maximum time a phase shall be serviced in
actuated operation. An external control signal shall be provided to
cause the controller to use the Max 2 setting instead of Max 1.
Maximum Initial Portion The limit of the computed initial portion on volume density timed
controllers.
Maximum Overall Length In lamps, the distance from the extreme bottom of the base to the
extreme top of the envelope.
Maximum 1 (MAX 1) Usually refers to a time limit applied to traffic actuated controls to
terminate the right-of-way and prevent massive delays to
opposing vehicles during heavy traffic. Termination by maximum
usually results in a recall placement to prevent trapping of
vehicles.
Maximum 2 (MAX II) An optional feature usually associated with coordination methods.
Provides two possible maximum settings for cycle or right-of-
way interval total time before termination begins.
Maximum Variable Initial An actuated controller setting, associated with Variable Initial, its
longest possible extension given to MIN green operating in
Variable Initial. See Seconds Per Actuation (S/A).
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Measure of Effectiveness
(MOE)
Indices of the effectiveness of the system in improving traffic
flow. Common bases of comparison include: volume, occupancy,
delays, speed, stops, and queue length.
Median The portion of a divided highway or street separating the traveled
ways for traffic in opposite directions.
Megger A device used by power companies to measure very high
resistance to earth ground. It’s use to measure the leakage
resistance of a wire's insulation to ground.
Megohm One million ohms, which is the unit of electrical resistance.
Memory The capability of the controller to remember the vehicle calls it
receives.
Memory, Locking The retention of an actuation for future utilization by the
controller.
Memory, Non-Locking A mode of actuated controller operation which does not require
detector memory.
Memory Off See Non Locking.
Mercury Switch One internal component of a controller housing/cabinet that shuts
down the power to the housing when not properly positioned.
Mercury Vapor Luminaire A lighting unit containing a mercury vapor lamp mounted within
a housing with a metal frame glass lens and a reflector.
Messenger Wire A steel cable used to support signal equipment.
MGVD See Magnetic Gradient Vehicle Detection.
Micro Henry (uh) A measure of inductance. See Inductance.
Microprocessor A device that uses the flexibility of computer electronics on a
limited scale. Microprocessors are basically microminiaturized
central processing units (CPU’s)
Microwave Detector With microwave detectors microwave energy is beamed toward
an area of roadway from an antenna mounted overhead or in a
side-fire position on a pole. The antenna is angled toward traffic
to create a Doppler effect on the reflected signal. When a vehicle
passes through the beam, the energy is reflected back to the
sensing unit (antenna) at a different frequency. The detector,
electronic unit, senses the change in frequency which is an
indication of the passage of a vehicle. The operating frequency is
usually either K-band (24gHz) or X-band (10gHz).
Mid Mast Arm Mount A signal head mounted at some point on the mast arm between
the end of the mast arm and the pole.
Min Green The guaranteed green time of a phase. If a time setting control is
designated as minimum green, the green time shall not be less
than that setting.
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Min Recall This shall place a demand call for service on a phase when it is
not displaying green which shall cause the phase to be serviced
each cycle for at least the minimum initial time programmed for
the phase, regardless of detector inputs.
Min Red
(Also called
Red Revert Time)
If programmed for a ring, a phase in its yellow or red clearance
interval may return to its green state if demand occurs and there
are no opposing calls. The MIN RED time begins at the end of
yellow clearance and may include any red clearance time. MIN
RED is the minimum time a phase must indicate red before
reverting to green. This feature eliminates the possibility of
GREEN-YELLOW-GREEN phase sequence.
Minimum Gap This shall be the minimum allowable time between actuations to
maintain the right-of-way, or the limit to which the gap shall
reduce, overrides Passage Timer.
Minimum “Initial”
Lumen’s
A minimum value of initial light output below which no more
than a specified percentage of individual lamps will be permitted.
Minimum Green This shall be the shortest time the added initial interval may be
serviced green.
Minimum Initial Portion See Fixed Initial Portion.
Minimum Red Indication Provision within the controller unit to assure a minimum RED
signal indication in a phase following the YELLOW change
interval of that phase.
Minimum Vehicle
Standard
A test unit that produces the minimum change in input for which
the detector system must sense and indicate passage or presence.
NEMA specifies a Class 1 vehicle (small motorcycle).
Minor Street or Minor
Highway
The roadway approach or approaches at an intersection normally
carrying the minor volume of vehicular traffic.
Minor Movement
Controller Unit
A device that can be added to a controller assembly to provide
subordinate phase timing.
MIST Management Information System for Traffic.
Modification Kit A device which is installed in an intersection controller to allow it
to be controlled by a computer master.
Modular Design A design concept such that functions are sectioned into plug in
units which can be readily exchanged with similar units.
Monitor An operating system software program which provides a uniform
method for handling the real-time aspects of program timing such
as scheduling and basic input/output functions.
Page -43-
Motion Detector A detector that detects the motion of a vehicle passing through the
zone of detection of the detector at some minimum speed usually
2 to 3 mph (3.2 to 4.8 kph). Vehicles traveling slower than the
minimum speed or stopped in the zone of detection are not
detected. See Passage Detector.
Mounting Brackets A grouping of parts used to fix a signal head in the operating
position.
Movable Bridge
Resistance Gate
A type of traffic gate, which is located downstream of the
movable bridge warning gate, that provides a physical deterrent to
vehicle and/or pedestrian traffic when placed in the appropriate
position.
Movable Bridge Warning
Gate
A type of traffic gate designed to warn, but not primary to block,
vehicle and/or traffic when placed in the appropriate position.
Movement The term used to identify the direction of travel and the approach
of a vehicle at an intersection, i.e., left turn, through or right turn.
See Phase.
Movement Detector See Passage Detector.
MS Connector A military standard for specifying quality and durability of
connectors.
Multimeter A meter that will preform several types of test ( i.e., voltage,
resistance, and amps).
Multiplexed DC A multiplex method which uses a combination of DC voltage
amplitudes to transmit or receive a message.
Multiplexing A communications technique which allows more than one item of
information to be transmitted or received at essentially the same
time.
Multipoint Channels Communications links (cable runs) which are wired in parallel at
multiple sending/receiving stations. Every message to or from any
incorporated sending/receiving station is transmitted over the
same cable pair.
MUTCD Flash See Remote Flash.
N
Nano Henry One billionth of a henry, from the unit of measurement of
inductance.
NEMA National Electrical Manufacturers Association.
Network A series of intersecting arterial’s or streets that are part of a
coordinated signal system. Can be an Open Network or Closed
Network.
Node Each signalized intersection in a traffic signal system. Also, each
one-way traffic stream between nodes is a link. See Link.
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Noise Random variations of one or more characteristics of any entity
such as voltage, current, and data. Generally, any disturbance
tending to interfere with the normal operation of a device or
system.
Noise (BND) NEMA
Conflict Monitor
Constant noise on the field output signal (load switch) may affect
the integrity of the input sample (conflict monitor) if it occurs
exactly within the narrow sampling “window”. Depending on the
severity and repetition rate of the input noise , a BND error may
be detected after the samples have been corrupted for a period of
30 to 200 line cycles.
Nominal Operating
Voltage
The AC rms voltage, 120VAC, at which photometric
performance and power consumption are specified.
Non Locking A mode of actuated controller operation which does not require
detector memory.
Non-Actuated Refers to a control type generally in the pre-timed category, but
can be one phase in any control which does not employ a vehicle
call. Right-of-way timing for the non-actuated phase is fixed
regardless of traffic volume except for possible dwell.
Page -45-
NON-Actuated Operation Two external controls are provided to program selected phases to
operate in a non-actuated mode. (Call to non-act 1 and 2). Any
phase timing module may be programmed to respond to either or
both control signals, providing different non-actuated phase
combinations. If a phase is called to non-actuated, it will register
permanent pedestrian and vehicle calls. Phases not called to non-
actuated will service, on demand, in their normal sequence.
Any phase called to non-actuated will be serviced for a minimum
green interval during which it may not be terminated, except by
the external control signal INTERVAL ADVANCE. After the
minimum green interval the right-of-way phase will attempt to
terminate and service opposing calls. In the absence of opposing
calls, the right-of-way phase will advance to rest. The minimum
green interval of a non-actuated phase will be the maximum green
time programmed, (MAX 1 or MAX 2). If INHIBIT MAX
TERMINATION is activated, the minimum green interval will be
either the programmed MIN INTERVAL time or pedestrian
WALK interval, whichever is greater.
The termination and advancement of a non-actuated vehicle phase
depends upon its associated pedestrian (demand) service. During
the minimum green interval the phase in service will activate its
associated ped WALK indications. If there is a conflicting call at
the end of the minimum green interval, the vehicle phase will
remain green while the ped clears. After ped clearance phase
service will advance. In the absence of opposing calls, the ped
will rest in WALK. If a serviceable conflicting call is then
registered, the pedestrian service must time ped clearance before
the phase may advance. In the absence of an associated ped
service, the phase may advance immediately. In the event the
conflicting call is lost during the ped clearance interval, the ped
will continue to clear and rest in DON’T WALK. The vehicle
phase may advance from rest immediately to service an opposing
call.
Non-adjustable Signal
(Fixed Face Signal)
A signal having the faces mounted in a framework so that the
indications are presented at a fixed angle.
Non-Compensated
Magnetic Detector
Any magnetic detector other than compensated magnetic detector.
Non-Conflicting Phase Non-conflicting phases are two or more traffic phases which will
not cause interfering traffic movements if operated concurrently.
Non-Directional Detector A detector that is capable of being actuated by vehicles
proceeding in any direction.
Non-Directional Motion
Loop Detector
An induction loop detector which is capable of being actuated by
the passage of a vehicle over any portion of the loop.
Page -46-
Non-Interconnected
(isolated) Controller
A controller for operating traffic signals not under master
supervision.
NON-Lock A vehicle call will normally be registered and stored until the
calling phase receives service. If NON-LOCK is programmed
calls on the phase or phases will be stored only for the actual
duration of the call signal from the detector. This feature only
affects phase service and not detector counting functions.
Non-Locking Detection
Memory
A selectable feature of the circuit design for a controller phase
whereby the call of a vehicle arriving on red (or yellow) is
forgotten or dropped by the controller as soon as the vehicle
leaves the detection area.
NTCIP National Transportation Communication Interface Protocol
O
Object Markings Markings intended for use on obstructions within or adjacent to
the roadway.
Observe Gap For observation use only. Passage time in effect for that phase
timing. Should be equal to operator set passage time at the
beginning of green and reduce down to min gap time according to
TBR and TTR.
Occupancy The percentage of roadway occupied by vehicles at an instant in
time. In general use, it is a measurement based upon the ratio of
vehicle presence time (as indicated by a presence detector) over a
fixed period of total time.
Occupancy Controller
Assembly
A traffic actuated controller which responds to the presence of
vehicles within an extended zone of detection.
Off Line Descriptive of a system, peripheral equipment or a process not
under the control of the central processing unit. See On Line.
Offset The time difference or interval in seconds between the start of the
green indication at one intersection as related to the start of the
green interval at another intersection or from a system time base.
The relationship between two or more intersection controls along
an artery such that vehicles starting at a reference point may
proceed along the artery at a predetermined speed without
stoppage. Is Accomplished by resetting each intersection control
from a master control to select the artery green point capable of
true progression.
Offset Interrupter A method of offset seeking which distributes over two or more
cycle lengths, any time required for large offset changes.
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Offset Seeking A process performed by the local controller to get in step (in
sync) with the master controller. When in sync, the local cycle
zero point is offset from the master’s sync pulse by
programmable value determined by the active offset period.
Offset Selection Choosing one of several possible offsets either manually or
automatically either by time of day or in response to some
directional characteristic of traffic flow.
Ohm The unit of electrical resistance equal to the resistance through
which a current of one ampere will flow when there is a potential
difference of 1 volt across it.
Omit All Red Clearance Excludes from the sequence of service, any all red clearance
times programmed for the phases in one ring for the duration of
the signal.
Omit, Phase A command that causes omission of a phase.
On Line Descriptive of a system, peripheral equipment or a process under
control of the central processing unit. See Off Line.
On Line Optimization A method by which a process; i.e., traffic signal pattern, is
continually adjusted in real time to seek the best obtainable set of
operating conditions.
Open Bottom Tunnel
Visor
A visor which encircles the entire lens except a segment equal to
approximately 2 inches of circumference at the bottom of the
lens.
Open Network A network where the arterial’s do not intersect more than once
(i.e., there are no closed loops in the system).
Open Loop System Pertaining to a control system in which there is no self correcting
action or feedback as there is in a closed loop system.
Optical Unit An assembly of a lens, reflector, light source, and other
components if required, with the necessary supporting parts to be
used for providing a signal indication.
Optically Programmed
Signal
A signal head containing optical units projecting an indication
which is selectively veiled so as to be visible only within desired
viewing boundaries.
OS Operating System
Outbound The traffic condition wherein an imbalance exists when a heavier
flow away from central points. Also described as the P.M. peak
period.
Overall Length (O.L.) The total distance from the tip of the bulb to the tip of the base,
including solder on the base eyelet (does not apply to PAR type
lamps).
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Overlap A right-of-way indication that allows traffic movement when the
right-of-way is being assigned to two or more traffic phases.
Overlap card This card is used to program overlaps in a controller. Most newer
controllers are now programmed by keyboard entries.
Overlap Load Switch
Drivers
The controller shall provide three outputs per overlap phase to the
load switches to indicate GREEN, YELLOW or RED for each
overlap.
Overlap Phase Assigns parent phases to overlap. Overlap will be green whenever
assigned parent phase is green.
P
Panel A board within the controller cabinet upon which are mounted
field terminals, fuse receptacles or circuit breakers and other
portions of the controller assembly not included in the controller
unit or auxiliary devices.
Parameter (1) A quantity in mathematics that may be assigned any arbitrary
value and that remains constant during some calculation; (2) a
definable characteristic of an item, device, or system.
Parity Check A summation check in which the binary digits in a character or
word are added, and then sum checked against a single,
previously computed parity digit; i.e., a check of whether the
number of ones in a word is odd or even.
Passage The time allowed for a vehicle to travel at a given speed from the
detector to the nearest point of conflicting traffic.
Also, a term functionally equal to and often used interchangeably
with Unit Extension.
Passage Detection The ability of a vehicle detector to detect passage of a vehicle
moving through the detection zone and to ignore the presence of a
vehicle stopped within the detection zone.
Passage Detector Vehicle detector that has the ability to detect the passage of a
vehicle moving through the detection zone and to ignore the
presence of a vehicle stopped within the detection zone.
Passage Mode Detector mode in which an output is given as long as a vehicle
remains in the field of influence. Also called Presence Mode.
Passage Period The time allowed for a vehicle to travel at a selected speed from
the detector to the nearest point of conflicting traffic.
Passage Time The timing interval during the extensible portion which is
resettable by each detector actuation. The green right-of-way of
the phase may terminate on expiration of the unit extension time.
Also known as Vehicle Interval or Preset Gap.
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Pattern A unique set of traffic parameters (cycle, split, and offset)
associated with each signalized intersection within a predefined
group of intersections (a section or a sub-zone).
Pattern Generation The process of computing the traffic parameters forming a pattern
from accumulated traffic data and the area geometry.
Pattern Matching A technique used to select a pattern based on comparing
measured traffic data with stored data associated with stored
patterns.
Pattern Selection Choosing one of several different patterns from a library of
patterns either manually, automatically as a function of time-of-
day, or traffic responsively.
PCPHPL Passage Car unit Per Hour of green time Per Lane.
Ped Clearance The controller shall provide an output for each phase which shall
indicate the phase’s associated ped phase is in its clearance
interval.
Ped Detector Activation of this signal shall cause the controller to register a
pedestrian call for the programmed phases associated pedestrian
phase.
Ped Omit Excludes from the sequence of service, any pedestrian WALK
intervals associated with a phase. All excluded calls registered
during the activation of this signal will be stored for service after
the signal is released.
Ped Recycle Activation of this signal shall allow pedestrian service in the
programmed ring to recycle if there is a pedestrian call registered
on the phase in service or pedestrian recall is programmed for the
phase and there are no serviceable opposing calls. Ped Recycle
shall be active during actuated and non-actuated operation and
shall be subordinate to PED OMIT.
Pedestal Mount See Post Mount.
Pedestal, Traffic Signal
(Post)
A vertical support on top of which the signal head or controller
assembly is mounted.
Pedestrian Any person on foot.
Pedestrian Actuated
Controller Assembly
A controller assembly in which intervals, such as pedestrian
WALK and CLEARANCE intervals, can be added to or included
in the controller cycle by the actuation of a pedestrian detector.
Pedestrian Clearance The interval during which the “DON’T WALK” indication is
flashed, starting after a “WALK” indication and ending before
conflicting vehicles receive a green indication.
Pedestrian Clearance Time The time provided for a pedestrian crossing in a crosswalk, after
leaving the curb or shoulder, to travel to the center of the farthest
traveled lane or to a median.
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Pedestrian Change
Interval
An interval during which the flashing UPRAISED HAND
(symbolizing DON’T WALK) signal indication is displayed.
When a verbal message is provided at an accessible pedestrian
signal, the verbal message is “wait”
Pedestrian Detector A detector that is responsive to operation by or the presence of a
pedestrian. This traditionally has been of the push button type,
installed near the roadway and operated by hand. Preferably it
should have some form of pilot light to indicate upon actuation
that the unit is operating, but this is rarely provided because of
susceptibility to vandalism. Also NEMA does not provide an
output to illuminate this indicator.
Pedestrian Load Switch
Drivers
The controller shall provide two outputs per phase to the load
switches to indicate WALK and DON’T WALK for each
pedestrian phase.
Pedestrian Permissive
Period
Provides an independent permissive period for ped timing, which
usually requires more guaranteed time than the vehicle. See
Permissive’s.
Pedestrian Phase A traffic phase allocated to pedestrian traffic which may provide
a right-of-way pedestrian indication either concurrently with one
or more vehicular phases, or to the exclusion of all vehicular
phases.
Pedestrian Push Button A momentary switch place at an intersection to enable a person to
call for the right-of-way at a crosswalk.
Pedestrian Recall This shall place a pedestrian demand call on a phase while it is
not being serviced which shall cause the pedestrian phase to
service, pedestrian walk and clearance intervals in its normal
manner each cycle without necessity of a push button actuation.
Pedestrian Recycle Any pedestrian service that begins after the associated green
phase.
The ability of the controller when resting in green on a phase to
return to a pedestrian movement after it has left that pedestrian
movement.
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Pedestrian Service A pedestrian movement will be serviced during its associated
vehicle phase if there is WALK time programmed and a
pedestrian call is registered.
A pedestrian call may exist either because: a) there is an actual
pedestrian actuation, b) ped recall is programmed on the phase
timing module, c) the phase is called to Non-Actuated, or d) the
controller is in Manual Control Enable.
In the event a ped actuation is required to register a call, the
actuation must be registered prior to the associated vehicle phase
green in order to obtain service; unless the Ped Recycle is
activated for a non-actuated phase or the phase is in a rest state. If
the call is registered before the vehicle phase, the ped WALK
interval will begin the same time as the vehicle green. Ped calls
will remain registered until serviced; unless they are registered
during the walk phase of their associated ped service.
Ped service may recycle during its associated vehicle phase under
certain conditions. In actuated operations, the ped may recycle if
there is a ped call for that phase and it is received during ped
clearance or DON’T WALK, and if there are no conflicting calls
received; or if PED RECYCLE is activated for that phase and
FORCE-OFF and PED OMIT are not active. In non-actuated
operation, the ped may recycle if the ped is in DON’T WALK;
HOLD and PED RECYCLE are activated for that phase, and
FORCE-OFF and PED OMIT are not activated for that ring. A
phase which is called to non-actuated may rest in WALK if, at the
end of the WALK interval there are no conflicting calls; or if
HOLD is activated for the phase and FORCE-OFF is not
activated for the ring. If the ped is resting in WALK and there is a
change in any of the above conditions, the ped will advance to
ped clearance. Ped clearance may be terminated only by
INTERVAL ADVANCE.
Pedestrian Signal A traffic control signal which is erected for the exclusive purpose
of directing pedestrian traffic at signalized intersections.
Pedestrian Signal Head A signal head, which contains the symbols WALKING PERSON
(symbolizing WALK) and UPRAISED HAND (symbolizing
DON’T WALK), that is installed to direct pedestrian traffic at a
traffic control signal.
Pedestrian Walk This shall be the time the associated phase indicates WALK.
Percentage Used in lieu of expressing time in seconds since many intervals
(which see) are a portion of the total cycle. The total cycle length
can be changed due to coordination, 100 percent is used to
indicate the total cycle length and the splits and intervals as a
percentage of that total.
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Percentile Speed Information obtained from intersection warrants relating to
vehicle speeds in an approach. Example: 80th
percentile speed:
that speed above which 80% and below which 20% of the speed
occurred in the approach.
Permissive Left Turn A left turn that can be made when conflicting traffic movement
permits with a green ball indication. This type of turn lane
usually has a five (5) section signal head installed to control
traffic movement.
Permissive Mode A mode of traffic control signal operation in which, when a
CIRCULAR GREEN signal indication is displayed, left or right
turns may be made after yielding to pedestrians and/or oncoming
traffic.
Permissive Period Relates to selected periods during coordinated operation in which
a call from the opposing phase can be acknowledged.
Permit Phases allowed to go to a green condition. Can allow from 1 to 8
phases.
Phase The part of the cycle allocated to any traffic movements or
combinations of traffic movements simultaneously receiving
right-of-way during one or more intervals. The controller sees
each phase as individual movements. Total of (8) possible phases
can be designated at each intersection for left turn and through
movements. Concurrent phases are protected, non-conflicting
phases that are timed together, such as “1+5", represent phase
number 1 and number 5 running together at the same time.
A traffic signal phase has two different meanings in traffic signal
terminology, as follows:
A.) NEMA: A vehicular phase is a phase which is allocated to
one specific vehicular traffic movement (e.g., east bound through
traffic as timed by a dual ring controller unit). See Conflicting
Phases and Non-Conflicting Phases.
B.) Traditional: A part of the cycle allocated to any specific
traffic movement receiving the right-of-way or to any
combination of traffic movements receiving the right-of-way
simultaneously during one or more intervals.
Phase Copy When entering phase timing data copying timing data from one
phase to another can be accomplished through the keypad.
Phase Diagram A diagram illustrating the sequence of phases at a intersection,
with movement arrows indicated for each phase and showing
overlaps, concurrent timing, etc.
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Phase Green Control A scheme for controlling an intersection controller whereby a
control circuit causes the controller to dwell in Phase Green
Intervals until released by the Master Control Unit, Minimum
green times and all fixed intervals are timed by the local
controller; offset, split and cycle length are controlled by the
Master Controller.
Phase Interval A part of the signal cycle during which the signal indication does
not change.
Phase Modular Controller A controller constructed so that each timing module is associated
with only one independent phase. The addition or removal of
modules associated with one phase will not affect the operation of
the controller with respect to the other phases.
Phase Next A controller output, when active, the associated phase is
committed to be next in sequence. The output will remain active
until the phase becomes active. The phase next decision is made
at the end of the green interval, the output is activated during the
clearance interval of the terminating phase.
Phase Omit Causes a phase to be excluded from the normal sequence of
service and prevents calls from being serviced on that phase for
the duration of the signal. This may extend the Added Initial time.
See Omit.
Phase On An output is provided per phase which indicates the phase is
currently being serviced in either green, yellow change, or red
clearance intervals.
Phase Overlap Refers to a phase which operates concurrently with one or more
other phases. See Overlap.
Phase Reversal For an 8 phase dual ring controller, in some cases, phase 1 and 2
in ring 1 could be reversed. The existing 1+5 phase would
become 2+5.
Phase Sequence The order in which a controller cycles through all phases. See
Sequence.
Phase Shift Keying (PSK) A modulation method employed to transmit data. The technique
of differentially coherent phase modulation is generally used as it
eliminates the difficulty of deriving a reference phase. In such a
system, each signal element is stored one element at a time and
the phase change between successive elements provides system
coherence and the desired reference.
Photoelectric Control An automatic switch controlled by ambient skylight intensity to
turn sign lighting on or off according to the changes of night or
day.
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Pick Up Procedures The orderly process or operations which are performed to bring a
controller(s) under the supervision and control of the System
Master.
PIN Personal Identification Number
Platoon A group of vehicles in motion. Similar to a Queue but differs in
that the group of vehicles are in motion. Has become the desired
method of establishing coordination. Allows a group of vehicles
of a certain smooth right-of-way along an artery.
Pneumatic Detector A pressure sensitive detector that uses a pneumatic tube as a
sensor.
Point Detection The detection of a vehicle as it passes a point or spot on a street or
highway. See Small Area Detector.
Pole Cap The weather proof covering on the top of a steel strain pole.
Pole, Traffic Signal A vertical support to which structural items and hardware are
attached for supporting traffic signals.
Police Panel A small access door on the controller housing/cabinet where
police can place the intersection on flash or if equipped with a
manual control device can override the normal operational timing
of the intersection.
Polling System A communications system that uses a systematic method,
centrally controlled, for permitting stations on a multipoint circuit
to transmit without contending for the interconnect line.
Polychloroprene Chemical name for Neoprene. Used for jacketing wire and cable
that will be subject to rough usage, moisture, oil, greases,
solvents, and or chemicals. May also be used as a low voltage
insulating material.
Polyethylene A family of insulating materials derived from the polymerization
of ethylene gas.. All members of the family are excellent
dielectrics. Electrically they are far superior to any other extruded
dielectric in use today. It has high insulation resistance, high
dielectric strength, and good abrasion resistance. Polyethylene is
being widely used for insulation on signal and detector wire and
cable. They are suitable for direct burial.
Polyolefins A family of plastics including cross linked polyethylene and
various ethylene copolymers which shrinks when heat is applied.
Commonly used in splicing.
Polypropylene A thermoplastic with good electrical characteristics, high tensile
strength, and resistance to heat.
Polysulfone A polymer highly resistant to mineral acid, alkali, and salt
solutions.
Page -55-
Polyurethane Enamel that has excellent moisture resistance, easily soldered,
and excellent winding properties.
Polyvinyl Chloride (PVC) A family of insulating compounds whose basic ingredient is
either polyvinyl chloride or its copolymer with vinyl acetate. Can
be either rigid as used in conduit for preformed detector loops or
flexible as used in duct tubing to encase detector wire. It is also
widely used as insulation material on wire known as type T and
TW used in detector applications. Known as PVC or Vinyl.
Post Mount A signal head mounted on the top of a post.
Power Consumption The electrical power in Watts consumed by an LED signal
module when operated at nominal operating voltage and ambient
operating temperature range.
Power Factor (PF) PF equals Watts divided by Volt-Ampere (VA) or the ratio of
power consumption in Watts to Volt-Amperes.
Power Head A small 3 x 6 ft (0.9 x 1.9 m) loop installed at the stop line end of
a long loop in order to improve the detection of small vehicles. It
usually has multiple turns of wire and may have an angle
configuration.
Power Line Switch A manual switch for disconnecting power to the controller
assembly and traffic control signals.
Pre-timed Control Refers to a type of intersection control where interval times are
not related to vehicle detector actuations but remain a fixed
percentage of the total cycle length.
Pre-Timed Controller
Assembly
A controller assembly for the operation of traffic signals with
predetermined : 1.) Fixed cycle length(s), 2.) Fixed interval
duration(s), and 3.) Interval sequence(s).
Preemption The term used when the normal signal sequence at an intersection
is interrupted and or altered in deference to a special situation
such as the passage of a train, bridge opening, or the granting of
the right of way to an emergency vehicle, or for other special
needs.
Pre-emptor The device used to accomplish preemption (i.e., Opticom).
Preferred Sequence Preferred sequence is the normal order of phase selection within a
ring with calls on all phases.
Prepare to Stop When
Flashing (PTSWF)
An integrated sign on the approach to the intersection that gives
an advance warning that the intersection is about to change from
the green to the yellow interval.
Presence Controller See Occupancy Controller Assembly.
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Presence Detector The ability of a vehicle detector to sense that a vehicle, whether
moving or stopped, has appeared in its field. The sensor may
cover a large area or be a series of small sensors wired together in
series, parallel, or series/parallel. True presence is when the pulse
duration is equal to the actual time the vehicle remains in the
detector field of influence.
Presence Holding Time The time that a detector system will continue to indicate the
presence of a vehicle over one of its loops without adjusting to
consider the vehicle a new environment. Upon making this
adjustment the actuation is terminated. NEMA requires that a
Class 2 vehicle (large motorcycle) be detected for a minimum of
3 minutes.
Presence Loop Detector An induction loop detector which is capable of detecting the
presence of a standing or moving vehicle in any portion of the
effective loop area.
Presence Mode Detector mode in which an output is given as long as a vehicle
remains in the field of influence. Also called Passage Mode.
Preset Gap See Passage Time.
Pressure Sensitive
Detector
A detector capable of sensing the pressure exerted by a vehicle
passing over the surface of its sensor. A detector used for well
over 40 years that consisted of two metal plates separated by
spacers. When a vehicle tire passed over the detector, it
compressed the spacers and allowed the two plates to make
contact, thereby closing an electrical circuit. This type of detector
normally produced two or more pulses per vehicle because each
axle would cause a contact.
Printed Circuit A conductive material applied to a non-conductive face to provide
a path for interconnection of electrical or electronic parts.
Priority of Input Function The priority of input functions shall be in the following order : 1.)
Power up, 2.) External start, 3.) Phase omit, 4.) Pedestrian omit,
5.) Interval advance, 6.) Stop timing, 7.) Manual control enable,
8.) Force off, 9.) Hold.
Priority Traffic Phase
Selection
A means by which, upon demand from priority traffic, the right-
of-way for such traffic is obtained or modified.
Probe The sensor form that is commonly used with a magnetometer type
detector.
Program A preset signalization sequence(s) from a master in the system
concept. May be electro-mechanically produced or Traffic
Adjusted by appropriate equipment and or computer.
Page -57-
Program Selection The process of selecting the appropriate program for a given set
of conditions. It can be accomplished manually or automatically
either by time-of-day or in response to some characteristic or
traffic flow.
Programmable Read Only
Memory (PROM)
A device which stores data that cannot be altered by computer
instructions. Data is stored “burned” into this device externally by
an electronic process. Some PROM’s can be erased and
programmed through special physical processes.
Progression Refers to coordination method based upon offsets between
intersections along an artery. Determined by time required to
travel from one controlled intersection to the next and adjusted to
give artery right-of-way without delay.
Progressive Flow Coordinated movement along an arterial at a given speed is
termed progressive flow.
Protected Left Turn A left turn that can only be made when a green arrow indication is
lite. This type of left turn lane has a three (3) section head with a
red indication.
Protected Mode A mode of traffic control signal operation in which left or right
turns may be made when a left or right GREEN ARROW signal
indication is displayed.
Protected Pedestrian
Clearance
This shall be the time the associated pedestrian phase indicates
the pedestrian clearance interval.
Pull Box A container usually at least 1 cubic ft. in size that is placed
underground with a removable cover flush with the ground
surface. Splices between lead in cable and loop lead in wires are
located here.
Pulse Mode The detector produces a short output pulse (between 100 and 150
ms) when a vehicle enters the sensor loop zone of detection. This
occurs even though the vehicle remains in the detection zone for a
longer time. See Detector Mode.
Pushbutton A button to activate pedestrian timing.
Pushbutton Locator Tone A repeating sound that informs approaching pedestrians that they
are required to push a button to actuate pedestrian timing and that
enables pedestrians who have visual disabilities to locate the
pushbutton.
Q
Q See Quality Factor.
Page -58-
Quadrupole A loop configuration that adds a longitudinal saw slot along the
center of the rectangle, so that the wire can be installed in a figure
eight pattern, thereby producing four electromagnetic poles
instead of the normal two. The design improves the sensitivity to
small vehicles and also minimizes splash over. Also spelled
Quadrapole and Quadripole in various documents.
Quality Factor A numerical index for rating the quality of a resonant circuit. A
higher number indicates less losses and increased detection
sensitivity in a resonant type detector system.
Queue A platoon or group of vehicles waiting at an intersection.
Queue Detector Component of a traffic control system which senses the presence
(or number) of vehicles waiting in a queue at an intersection or on
a freeway ramp.
Queue Length Number of vehicles that are stopped or slowly moving in a line
where the movement of each vehicle is constrained by that of the
lead vehicle.
R
Rack Mounted Detectors Detector units that have no enclosing case and, therefore, must be
placed in the controller cabinet by inserting its printed circuit
board into a wired receptacle or “rack” made for the purpose.
Compare Shelf Mounted Detectors.
Radar Detector A vehicle detector installed above or adjacent (side mounted) to
the roadway capable of being activated by the passage of a
vehicle through its field of emitted microwave energy.
Radio Frequency Detector A vehicle detector consisting of a loop of wire embedded in the
roadway that is tuned to receive a preselected radio frequency
from a transmitter located on a vehicle.
Radio Interference
Suppressor
A device inserted in the power line in the controller cabinet that
minimizes the radio interference transmitted back into the power
supply line, which interference may be generated by the
controller unit or other mechanisms in the cabinet.
Raised Pavement Markers
(R.P.M.’s)
Low profile housings incorporating recessed plastic inserts and
convex bottoms with parallel ridges which are epoxy bonded to
matching pavement positions prepared with an arbored concavity
and saw cuts.
Rake Strain poles adjusted initially out of plumb but drawn to
verticality under the span wire tensioning.
Ramp A traffic way usually inclined, over which traffic passes to make
connections with other ways.
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Ramp Control Signal A highway traffic signal installed to control the flow of traffic
onto a freeway at an entrance ramp or at a freeway-to-freeway
ramp connection.
Ramp Meter see Ramp Control Signal.
Random Access Memory
(RAM)
A storage device with both read and write capabilities that will
allow random access to stored data.
Rated “Initial” Lumen’s The average amount of luminous flux (light) produced by
statistically acceptable sample of lamps on operation at rated
voltage after having been seasoned to one half to one percent of
rated life.
Rated Life The (arithmetic) average of burning hours for a sample number of
lamps operated at rated volts and defined operating conditions.
Rated Voltage The nominal or design operating voltage of the lamp; the voltage
at which rated watts, lumen’s, and life are determined.
Rated Watts The average initial power (watts) consumed when the lamp is
operated at rated volts.
Re phase The process of resetting, after a pulse actuation, to enable another
pulse actuation should another vehicle enter the detection area.
Can also be used as a verb: “The detector shall re phase 2 seconds
after initiating an output pulse.”
Reactance The reactance (ohms) of a circuit component is the product of the
voltage across the component and the sine of the phase angle
between the voltage and the current divided by the current
through the component assuming sinusoidal operation.
Read Only Memory
(ROM)
A storage device not alterable by computer instructions, for
example, magnetic core storage with a lock out feature or punch
paper tape. ROM requires a masking operation during production
to permanently record programs or data patterns in it.
Synonymous with non-erasable storage, permanent storage, and
read only storage.
Real Time Batch Monitor
(RBM)
A system or device which monitors the demands of the real time
system (foreground processing) so that as time becomes available,
the system will be automatically freed to begin batch processing
(background processing).
Real Time Clock A clock which indicates the passage of actual time of day rather
than a clock set by the computer to measure an arbitrary interval
of time (same as time of day clock).
Real Time Control The processing of information or data in a sufficiently rapid
manner so that the results of the processing are available in time
to influence the process being monitored or controlled.
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Recall An operational mode for an actuated controller whereby a phase,
either vehicle or pedestrian, is displayed each cycle whether
demand exists or not. Usually in a temporary or emergency
situation. If recalls are not selected, internally or externally, the
controller will advance to a rest state in the absence of actuations.
If Recall is programmed, a call will automatically be registered if
a conflicting phase is serviced. See MIN Recall, MAX Recall,
PED Recall, Soft Recall, Extendable Recall, and CNA.
Recall Switch A manual switch which causes the automatic return of the right-
of-way to its associated phase regardless of the operation of a
detector in that street.
Receiver A part of the communication system which accepts and translates
(decodes) signals into command or data functions in a control
system.
Red Clearance Interval A clearance interval, which may follow the yellow change
interval, during which both the terminating phase and the next
right-of-way phase display red.
RED FAIL indicator
(NEMA)
The RED FAIL indicator will be illuminated when an absence of
signal (dark signal head) is detected on a channel(s). The Channel
Status display will show all channels on which the fault occurred.
Red Lock Locks in vehicle call placed on a phase when in red condition.
Red Out A means used to satisfy the conflict monitor observation of a
channel without having to place a signal lamp on the field
terminal.
Red Rest Activation of this signal shall cause the phases in the programmed
ring to indicate RED when in the rest condition. This signal shall
be effective for its duration and shall not be effective during non-
actuated operation.
A feature whereby, in the absence of demand, the controller will
return to all red instead of resting in green of the last serviced
phase.
Red Revert The minimum amount of time the controller can leave the red
indication of a phase and return to the green indication of the
same phase.
Reel A spool of tape, generally magnetic tape.
Reference Offset Point for which offset is calculated from the start of coordination
phases 2 or 6 or, phases 4 or 8.
Reflector A contoured reflective surface which redirects the light from the
light source toward the lens.
Register A device used for the temporary storage of one or more words to
facilitate arithmetic, logical or transferral operations.
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Rejection (Adjacent Lane) The ability of a detector not to output an unwanted actuation
caused by a vehicle in a lane adjacent to that in which the detector
is located.
Relay An electromagnetic switching device, having multiple electrical
contacts, energized by electrical current through its coil. It is used
to complete circuits.
Reluctance The opposition which a magnetic material or magnetic circuit
offers to the passage of magnetic lines of force. Reluctance is the
reciprocal of permeability (the ability of a metal to conduct lines
of force) and permeance (the measure of that conductivity).
Therefore, reluctance is related to permeability and permeance in
much the same way as resistance is related to conductance in
electric circuits.
Remote Flash An input, when energized, causes normal signal operation to be
discontinued and specified signal light to be operated in a flashing
manner.
Remote Terminal An input/output unit physically removed from the central facility
but connected by means of a communication line.
Repeater A device used to amplify and/or reshape signals.
Reset The action in an intersection control which causes the control to
begin its cycle at a new position in time in relation to a reference.
Resetting a control assures a desired offset between intersections
in a progression system at all times.
Resin An organic substance that is non-conductor of electricity. Resins
are widely used for insulation and encapsulation.
Resistance The opposition that a device or material offers to the flow of
direct current, equal to the voltage drop across the element
divided by the current through the element. (R=V/I)
Resonant Frequency The natural vibration frequency of a loop and its lead-in wire, to
which the detector unit must tune.
Response Time The time a detector takes to respond to the initiation of a
detection by a vehicle.
Responsive Mode A system operation wherein the selection of signal timing
programs is based on current traffic data as input by vehicle
sensors within the network.
Rest The state in which the controller unit remains until called out of
that phase.
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Restart NEMA controllers may be programmed to restart in FLASH,
ALL RED, and or first phase GREEN or YELLOW. If FLASH or
ALL RED are programmed the controller will restart in the
selected mode for the time programmed in FLASH / ALL RED
time. If both FLASH and ALL RED are programmed, the
controller will restart in flash for the time programmed. Restart
places a recall to minimum green on all phases and associated
pedestrian phases.
The phase or phases to be serviced first may be selected and
service will commence with the programmed phase first. It will
be serviced either green or yellow as programmed. Any phase on
the same side of the barrier in the opposite ring, programmed
under first phase will service concurrently.
If allowable phases in the opposite ring are not programmed the
phases in that ring will begin with the first in order. If start up in
YELLOW is programmed, only the first phases programmed and
their associated overlap phases will start in yellow for their
programmed yellow change time. If both YELLOW and GREEN
are programmed, the first phase or phases will start in yellow.
After the first phases are serviced the remaining phases will be
serviced in order and normal controller operation will resume.
RESTART will commence with restoration of power after a
power down, or it may be initiated by the EXTERNAL
RESTART control signal. Activation of this signal will cause the
controller to stop timing all intervals, releasing the signal will
initiate RESTART.
Restrictive Phase Assign two phases from Side 1 and/or two phase from Side 2.
When assigned, these phases will not be allowed to be on at the
same time. The assigned phases should be a lead phase from one
ring and the lag phase from the other ring. The other two phases
on the side should be on recall. (W4IKS)
Right-Of-Way The permitting of vehicles and/or pedestrians to proceed in a
lawful manner in preference to other vehicles or pedestrians by
the display of signal indications.
A movement has the right-of-way on a green signal with some
legitimacy during the yellow clearance interval.
Rigid Mast Arm Mount A mast arm mount where the signal head is rigidly affixed to the
mast arm to prevent any relative movement between the signal
and the arm.
Ring A ring consists of two or more sequentially timed and
individually selected conflicting phase so arranged as to occur in
an established order.
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Roadway Network A geographical arrangement of intersecting roadways.
RR Railroad
RS-232 Interface Standard interface between data terminal equipment and data
communication equipment employing serial binary data
interchange.
RTC Real Time Clock.
RTS Ready to Send.
RXD Receive Data
S
Sag The amount of deflection at the lowest point of span wire used for
the mounting of signal heads.
Sample Rate The rate at which measurements of physical quantities are made;
e.g., the number of times each second that a computer senses the
status of a data sensor as a loop detector.
Sampling Detector Any type of vehicle detector used to obtain representative traffic
flow information and transmits data to a computer for evaluation.
Sampling Period The length of time between each sample of a sensor. (Equal to
1/sampling rate.)
Scanning Detector A multi-channel detector in which the loop(s) of each channel are
energized in sequence, one at a time, in quick succession.
Scanning System A system which senses the status of multiple points, such as
detectors, and/or transmits commands to multiple points such as
slave controller units in a predetermined sequence and time
schedule.
Schematic Diagram A drawing using symbols to indicate the point to point connection
of all electrical or electronic parts.
Sealant The material used in a saw slot of a loop detector to seal the wires
in the slot.
Secondary Controller
Operation (slave)
A method of operating the traffic signals under the supervision of
a master controller.
Secondary Coordinator A device used to supervise the cycle of an associated traffic
actuated controller to permit synchronization and operation
allowing passage of platoons of vehicles in a progressive traffic
system.
Secondary or Local
Controller
See Controller.
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Seconds Per Actuation
(S/A)
An actuated controller setting, associated with variable initial.
When a vehicle passes over a detector, a tabulation begins (S/A
amount for each actuation), each successive actuation adding to
the previous. The S/A amount is compounded until it overrides
the MIN green period, and at that point becomes the new MIN
green. See Maximum Variable Initial.
Section Blank Door A section which closes the face of the housing (signal head
section) but does not support a lens, i.e., closes a housing in
which no optical unit is used.
Section Door The part of a signal section (signal head) which closes the face of
the housing and supports the optical unit lens.
Section Housing The part of a signal section which encloses, protects, and supports
the optical unit.
SE Special Event
Self Powered Vehicle
Detector (SPVD)
A detector buried in the pavement that uses a self contained
battery for power and transmits the detector information to the
controller without the need for direct connection (lead-in cable).
Self Tracking Detector A loop detector unit, not necessarily self tuning, that includes
electronics that compensate for environmental drift.
Self Tuning Loop
Detector Unit
One that is capable of adapting its operation to the resonant
frequency of the loop and lead-in wire without any manual
adjustment required. The term applies particularly to the start-up
of the detector’s operation, upon turn-on. Compare Self Tracking
Detector.
Semi Actuated Identifies type of intersection control with one or more phases
lacking vehicle detector input capability.
Semi-Actuated Controller
Assembly
A type of traffic actuated controller assembly in which means are
provided for traffic actuation on one or more but not all
approaches to the intersection.
Semiconductor A conductor whose resistivity is between that of metals and
insulators in which electrical charge carrier concentration
increases with increasing temperature over a specific temperature
range.
Sensing Zone See Zone of Detection.
Sensitivity As it relates to a loop system the change in total inductance of a
system caused by a minimum vehicle at one loop, expressed as a
percentage of the total inductance. As it relates to a detector, is
the minimum inductance change in percent required at the input
terminals to cause the detector to actuate.
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Sensor Loop An electrical conductor arranged to encompass a portion of the
roadway to provide a zone of detection and designed in such a
way that the passage or presence of a vehicle in the zone causes a
decrease in the inductance of the loop that can be sensed for
detection purposes.
Sensor (System and
Local)
Traffic detection devices (detectors) that permit the system master
or a local controller to obtain information as to the traffic flow
characteristics in the area of the sensor. (See Detector.) NEMA
limits the meaning of “sensor” to the sensing element of a
detector.
Sequence The order in which signal intervals are displayed around an
intersection on a pre-timed control or with calls all around on an
actuated control.
Sequential Phase will time passage after Min Initial has timed out, also Max
time starts after Min Initial. Passage will also be timed after
Flashing Don’t Walk.
Sequence, Interval The order of appearance of signal indications during successive
intervals of a cycle.
Sequence (short or absent
Yellow) Monitoring
This function detects the absence of a minimum period of an
active Yellow field signal output during a Red to Green to Yellow
to Red sequence. A sequence (short or absent Yellow) fault, if
enabled, will trip the monitor into a fault condition placing the
signal on a flashing operation.
Sequential Timing The arrangement of phases at multi-phase intersections into a
sequence in which the phases will occur consecutively. (1-2-3-4-
5-6-7-8)
Series-Parallel Type of electrical interconnection of four 6 x 6 ft (1.8 x 1.8 m)
loops, usually 9 ft (2.7 m) apart and installed in a line in one lane
to give a 51 ft (15.3 m) length of detection area. This
interconnection scheme gives a combined inductance close to
optimum.
Service Disconnect Switch See Power line switch.
Serviceable Conflicting
Call
A call which: a) occurs on a conflicting phase not having the
right-of-way at the time the call is placed; b) occurs on a
conflicting phase which is capable of responding to a call; or c)
when occurring on a conflicting phase operating in an occupancy
mode, remains present until given its right-of-way.
Sheath The outer covering or jacket over the insulated conductors to
provide mechanical protection for the conductors.
Shelf Mounted Detectors Units that have an enclosing case and, therefore, can be located in
the cabinet by placing them on a shelf. They can stand alone.
Compare Rack Mounted Detectors.
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Shield A conductive material surrounding the twisted pair(s) of wires in
the lead-in cable of a loop detector installation, so that outside
electrical interferences will not induce noise into the twisted
pair(s).
Short Yellow A term used to describe one function of the NEMA plus conflict
monitor. When the yellow clearance interval of the traffic
controller fails to time at least the minimum 2.7 - 3.0 seconds of
yellow clearance require by NEMA.
Shorted Turn Model A shorted turn model is a lossless shorted, single turn loop with
size and shape equal to the perimeter of the vehicle located above
the loop at the average vehicle undercarriage height.
Side Fire Detector A vehicle detector with its sensor located to one side of the
roadway, such as on a pole, rather than directly over the roadway.
Side Mount A signal mounting arrangement where the signal head is mounted
parallel to the vertical axis of a pole. See Bracket Mount.
Single Entry A mode of operation in a dual ring traffic controller that permit
the timing of a single phase where no demand is needed on the
permitted other phase(s).
Signal An optical device which is electrically operated by a controller
and visually communicates a prescribed action or actions to
traffic.
Signal Bus The termination point of the field wiring in a controller housing
for signal heads. When energized by the load switch 110 volts
AC is present at these terminals.
Signal Coordination The establishment of timed relationships between adjacent traffic
control signals.
Signal Face A section or combination of sections, each capable of displaying
its indication in one direction.
That part of a signal head provided for controlling traffic in a
single direction. Turning indication arrows may be included in a
signal face.
The front part of a signal head.
Signal Hardware A grouping of parts used to fix signal faces in relation to each
other to make a signal head.
Signal Head An assembly containing one or more signal faces together with
the associated signal housings, which may be designated as one-
way, two-way, etc.
Signal Housing That part of a signal section that protects the light source and
other required components.
Page -67-
Signal Indication The illumination of a traffic signal lens or a combination of
several lenses at the same time.
Signal Installation All of the equipment and material involved in the control of
traffic at one or more intersections by a single controller
assembly.
Signal Lamp A rugged bulb with extended hours of life, used in traffic signal
heads.
Signal Lamp Orientation In order for the signal lamp to reflect light correctly the bulbs
must be installed with the open end of the filament facing up.
This also helps the heat generated by the lamps to escape
extending the life of the lamps.
Signal Lens That part of the signal section that redirects the light coming
directly from the light source and its reflector, if any.
Signal Load Switch A device used to switch power to the signal lamps.
Signal Phase The right-of-way, yellow change, and red clearance intervals in a
cycle that are assigned to an independent traffic movement or
combination of movements.
Signal Section The optical unit and housing capable of displaying one indication.
Signal Shut Down Switch A manual switch to discontinue the operation of traffic control
signals without affecting the power supply to other components in
the control cabinet.
Signal Support The physical means whereby a signal head is supported in a
particular location.
Signal System Two or more signal installations operating in coordination.
Signal Timing The amount of time allocated for the display of a signal
indication.
Signal Visor That part of a signal section that directs the signal indication
specifically to approaching traffic and reduces the effect of
directed external light entering the signal lens.
Signal Warrant A threshold condition that, if found to be satisfied as part of an
engineering study, shall result in analysis of other traffic
conditions or factors to determine whether a traffic control signal
or other improvement is justified.
SIGOP (Traffic Signal
Optimization Program)
A computer program for determining optimum traffic signal
timing for street networks. The SIGOP system consists of six
program blocks written in FORTRAN IV language.
Simulation A pseudo-experimental analysis of an operating system by means
of mathematical or physical models that operate in a time
sequential manner similar to the system itself.
Page -68-
Simultaneous Coordination method whereby all signals along an artery give the
same indications to given street at the same time.
Simultaneous Gap-Out If Simultaneous Gap is programmed in dual ring operation, a
phase may re-extend out of green rest in response to a demand,
providing the phase in the opposite ring is not in gap-out, max-out
or a green rest state. Both phases must be in the gap-out, max-out
or rest states together before they will advance.
Simultaneous Gap Out
Inhibit
A feature that disallows a phases’s passage timer from starting up
again once it has timed out.
Single Entry Single entry is a mode of operation (in a dual ring controller unit)
in which a phase in one ring can be selected and timed alone if
there is no demand for service in a non-conflicting phase on the
parallel ring.
Single Ring Controller
Operation
A controller unit that operates two or more sequentially timed and
individually selected conflicting phase so that they occur in an
established order.
Skip Phasing The ability of a controller to omit a phase from its cycle of
operation in the absence of demand or as directed by a master
control.
Slave A local control device whose interval timing and sequence of
operation is controlled by a sub-master in a distributed system.
Slip-fitter A mounting bracket which provides for mounting a signal head
onto the top of a post or pedestal.
Small Area Detector A detector intended to detect vehicles at a spot location upstream
of the stop line. They may detect more than one lane. The 6 x 6 ft
(1.8 x 1.8 m) loop detector is a prominent example. Also,
included are ultrasonic and radar units, whose detection areas
may be as long as 20 to 30 ft (6 to 9 m), because the length of
time the moving vehicle is in the detection zone is not used in the
intersection control logic. This detector is also referred to as a
Point Detector.
Socket The part of the optical unit which supports the lamp and is so
arranged as to fix the position of the light source with reference to
the focal point of the reflector.
Soft Recall A form of “extendable recall” except the phase is only served if
no other “real calls” exist. Real calls are those for which there is a
detector input actuation.
Software Programs that facilitate the efficient operation of a system, such
as data bases, operating systems, and application programs.
Solid Spreader A signal bracket having solid arms radiating from a hub and used
at the bottom of a multi-face signal.
Page -69-
Solid State Device A device which is characterized by electrical circuits, the active
components of which are semi-conductors, to the exclusion of
electro-mechanical devices or tubes.
Sonic Detector A vehicle detector which emits sound energy from a transducer at
a high frequency (one that is in the upper range of human
hearing) and that senses the reflection of its energy from a vehicle
in its field.
Sound Sensitive Vehicle
Detector
A detector that responds to sound waves generated by the passage
of a vehicle over the surface of the sensor.
Span Wire Clamp See Span Wire Hanger.
Span Wire Hanger A mounting bracket for supporting a signal head by clamping
onto the span wire.
Span Wire Mount A signal head suspended over the roadway on messenger wire.
Span Wire, Traffic Signal One or more cables used as a means of support for traffic control
devices.
Special Event
Programming
A traffic pattern timing routine stored in memory which is
activated to compensate for unusual traffic flow caused by a
special event, such as a football game. Also see Exception Days.
Speed Analysis System A type of hardware assembly composed of two loop detectors and
auxiliary logic. The two loops are in the same lane, a precise
distance apart. A vehicle passing over the loops produces two
actuations. The time interval between the first and the second is
measured, and a speed is computed.
Speed Limit Sign Beacon A beacon used to supplement a SPEED LIMIT sign.
Speed Trap Two or more detectors strategically positioned and spaced, to
permit the computation of vehicle speed by measuring the time
between actuations as a vehicle passes from one sensor to the
next.
Splash-over An unwanted actuation caused by a vehicle in a lane adjacent to
that in which the detector is located. Often occurs where long
loops are used.
Splice Box See Pull Box.
Splice Kit All the materials need to make a complete water proof connection
of two cables.
Split A percentage of the cycle length allocated to each of the various
phases in a signal sequence (normally expressed in percent).
Split Phase That portion of a traffic phase that is separated from the primary
movement to provide a special phase that is related to a parent
phase and characterized by the inability to rest in a minor phase.
Page -70-
Split Selection The process by which a split is selected or calculated by the
computer based on a measurement and comparison of directional
demand as directed by system sensors or predetermined by time
of day clock. Also see Adaptive Split Selection.
Split Selection Switch A device on solid state controller units which when operated
discontinues automatic selection of split changes which are
independent of cycle length changes and permits hand selection
of such split changes.
Spreader, Solid A signal bracket having solid arms radiating from a bud and used
at the bottom of a multi-face signal.
Spreader, Tubular A signal bracket having tubular arms radiating from a hub
through which wiring can be passed to provide electrical
interconnection of the signal faces supported by the signal
bracket.
SPVD See Self Powered Vehicle Detector.
SRAM Static Random Access Memory
Standard Visor See Cutaway Visor.
Standby Mode A mode of operation whereby the controllers operate
independently of the central computer, usually in an emergency
condition, but is capable of responding to central computer
control when necessary.
Standby System Local control components which operate the intersection signals
upon failure of the communications link to the computer or when
the intersection is in standby mode.
Standby Transition The act of changing to or from a standby mode. See Drop
Procedures, Pick Up Procedures.
Start up Green First phases turned on after the restart from a long power failure.
Steady (Steady Mode) The continuous illumination of a signal indication for the duration
of an interval, signal phase, or consecutive signal phase.
Steady Burning Electric
Lamps
A series of low-wattage yellow electric lamps used to mark
obstructions or hazards in construction and maintenance work
areas.
Stop Bar See Stop Line.
Stop Beacon A beacon used to supplement a STOP sign, a DO NOT ENTER
sign, or a WRONG WAY sign.
Stop Line A line which indicates where vehicles should stop when directed
by a traffic control device
Page -71-
Stop Timing An external command that causes the controller to cease timing
all intervals currently being timed in a ring. Ring signalization
will dwell in the same state as long as STOP TIMING is
activated. Upon release of the signal, all intervals that were
stopped will be re-timed completely and normal controller
operation will resume.
Stops The number of times vehicles stop in the system. Used as a
measure of effectiveness to assess the effectiveness of a timing
pattern. A computer controlled system goal is to minimize stops.
Storage Area The area, usually expressed in terms of the number of vehicles,
between the stop line and the detector located upstream. In pre-
timed control it may be the number of vehicles arbitrarily used to
determine green time.
Stored Pattern A traffic control timing routine, stored in the computer memory,
which is activated on a time-of-day basis or when sensed traffic
demand conditions warrant.
Strain Bolts The large bolts used to secure the steel strain poles to the concrete
foundations.
Strain Pole A vertical support to which messenger wire and hardware are
attached for supporting traffic signals.
Street Equipment That equipment or hardware that is located “on the street” such as
an intersection controller assembly, signal heads, and detectors.
Stretch Detector See Extended Call Detector.
Sub-master A control unit capable of supervising a group of local control
units (slaves) according to commands from the central computer
master. Sub-masters are normally employed in distributed
systems.
Subordinate Phase (Minor
Phase)
A traffic phase in which the right-of-way is dependent on the
related operation (leading or lagging) of a specific independent
phase. A subordinate phase cannot occur independently of its
associated phase (parent phase).
Summator (1) A parallel to serial convertor. (2) An electronic or electro-
mechanical device that can take simultaneous (parallel) inputs
from loop detectors (or other contact output devices) and feed
them out one at a time (serial). (3) A device that eliminates
problems caused by coincidental input pulses (caused by two or
more vehicles simultaneously actuating different detectors
feeding one counter or controller) by momentary electronic
storage of the pulses until the counter can accept them.
Sun Phantom The effect of an outside light source entering the optical unit and
being returned in such a manner as to present the appearance of
the optical unit being illuminated.
Page -72-
Supervisory Refers to master control equipment which generates programs to
several intersection controls based upon clock, computer or other
traffic adjusted equipment.
Support, Traffic Signal The physical means whereby a signal head is supported in a
particular location.
Suppressor, Radio
Interference
A device inserted in the power line in the controller assembly
(cabinet) that minimizes the radio interference transmitted back
into the power supply line, which interference may be generated
by the controller or other mechanisms in the cabinet.
Surveillance The process of observing traffic performance through the use of
detectors.
Switch, Auto-Manual A device which, when operated, discontinues normal signal
operation and permits manual operation.
Switch, Flash Control A device which, when operated, discontinues normal signal
operation and causes the flashing of any predetermined
combination of signal indications.
Switch, Power Line A manual switch for disconnecting power to the controller
assembly and traffic control signals.
Switch, Signal Shut Down A manual switch to discontinue the operation of traffic control
signals without affecting the power supply to other components in
the controller cabinet.
Synchronization (1) Refers to motors or cam switches which are designed to
remain in step or in the correct rotational relationship at all times.
(2) Internal circuitry used to be sure several circuits begin actions
from the same reference point.
Synchronous-Motor
Controller
A controller operated by a synchronous motor which maintains a
constant speed determined by the frequency of the alternating
current power supply.
Synchronous Data
Transmission
A type of data transmission in which each character consists of 5
to 8 information bits depending on the code structure. There are
no start and stop bits. Timing is derived through synchronizing
characters at the beginning of each message or block of data. Also
see Asynchronous Data Transmission.
Synchronous Motor
Controller Unit
A controller unit operated by a synchronous motor which
maintains a constant speed determined by the frequency of the
power supply circuit.
System Two or more traffic control devices operating in coordination.
System Detector Detectors located to provide information to central control
computers selecting appropriate control programs to meet the
traffic demands.
Page -73-
System Management The act of directing, coordinating and/or controlling the design
and implementation phases of a system.
System Shutdown (1) Emergency system shutdown involves the failsafe turning off
of some or all system components due to power failure or
equipment failures. (2) Planning system shutdown consists of the
turning off of some or all system components by manual or
automatic means, usually for maintenance or off line tasks.
System Status The operational condition of each monitored remote control unit
or data sensing station in the system as indicated by a display or a
printout.
T
Table Look-Up (1) A process of obtaining information previously stored rather
than creating information based on calculations; (2) in control
systems, the process of selecting pre-stored timing programs
rather than generating timing programs based on real time
calculations.
Tape Switch A temporary detector consisting of two strips of metal encased in
a flat ribbon that is temporarily affixed to the roadway. When a
vehicle tire crosses the tape switch, the two metal strips make
contact closing an electrical circuit.
TBC Time Base Coordination.
TDM See Time division Multiplexing.
Telegraph Grade Circuit A circuit in which the maximum signaling rate is 75 baud,
generally considered sufficient for teletypewriter transmission.
Telemetry The automatic transmission of data over long distances.
Terminal Any fitting used for making a convenient electrical connection.
Terminal Blocks, Field Devices for connecting all wires entering the controller cabinet.
Terminal Bracket See Terminal Compartment.
Terminal Bus The blocks where wires are terminated.
Terminal Compartment A compartment having a terminal block for connecting signal
control conductors and which may support the signal face.
Terminate Applies most frequently in traffic control to the end of a timing
interval. Termination of right-of-way begins in an active phase
when a call is received from an inactive phase in a full actuated
control; right-of-way termination must always include adequate
intervals.
Test Input (Two per Unit) Test input, two per unit, for manufacturer’s use only, not
specified. Labeled Test input A and B.
Page -74-
TF The UL designation for fixture wire, solid soft copper conductor,
insulated with thermoplastic.
TFF Same as TF, except has stranded copper conductor.
THHN Building wire, plastic insulated, 90 degree Celsius, 600 volt,
nylon jacketed.
This Phase Next See Phase Next.
Three Bolt Clamp The device used to clamp span wires together.
Threshold A preset level (value) of a parameter which indicates that a
change of activity will occur if the current value is above or
below this level.
Through Band The time in seconds elapsed between the passing of the first and
last possible vehicle in a group of vehicles moving in accordance
with the designed speed of progressive signal system. See Green
Band or Band Width.
Through Movement A movement at an intersection which continues in a straight line
and across the intersection; does not turn in any direction.
THW Building wire, plastic insulated, heat, flame, and moisture
resistant, 75 degree Celsius.
THWN Same as THW with overall nylon jacket.
Tie Rod See Braced Type Mast Arm.
Time Base Coordination
(TBC)
Coordinated operation in response to internally generated time
clock commands selecting cycle, split, and offset.
Time Before Reduction
(TBR)
This shall be the interval between the beginning of the phase
green and the time the reducible gap function begins. If Max
Extension is programmed, then Time Before Reduction shall not
begin until the end of the INITIAL period. During the process of
GAP REDUCTION, it is the time period before the Gap reduction
process takes place.
Time Clock A device for the automatic selection of modes of operation of
traffic signals in a manner prescribed by a predetermined time
schedule.
Time Division
Multiplexing (TDM)
A technique for transmitting several different messages over one
communication channel by dividing a fixed interval of time into
several time slots and sending a discrete message within each
time slot.
Time Headway The time separation between vehicles approaching an
intersection, measured from the front of a vehicle to the next
vehicle.
Time of Day Patterns Signal timing plans selected according to the time of day.
Page -75-
Time Reference Point A point in time which serves as the time reference signal; i.e., in
the signal system for any one street, the time-space diagram is
normally expressed in terms of the offset between each signal in
the system and one particular signal which serves as the time
reference signal. The start of the green time reference signal on
this street is defined at the time reference point.
Time Share The use of a device for two or more purposes during the same
overall time interval, accomplished by interspersing component
actions in time.
Time Space Diagram A semi-pictorial presentation of two or more intersections being
coordinated that shows the offset, cycle, distance relationships.
Time Switch A device for the automatic selection of modes of operation of
traffic signals in a manner prescribed by a predetermined time
schedule.
Time To Reduce This shall be the interval over which the allowable gap between
actuations is shortened from Preset Extension to a Minimum
Extension by the Reducible Gap feature.
Time Zero The reference point used in coordinated systems to identify
offsets along the artery.
Timer The timing unit in a controller cabinet. Most often referred to as
the controller. Also see Controller Unit.
Timer Gear One of a set of different diameter gears determining the cycle
time of a timer dial when inserted into the drive train.
Timing, Analog Pertaining to a method of timing that measures continuous
variables such as voltage or current.
Timing Control A calibrated device that provides a time setting for a interval or
portion of a interval.
Timing Dial That part of a controller which times one cycle length and its
associated split(s) and offset(s).
Timing, Digital Pertaining to a method of timing that operates by counting
discrete units usually based on the frequency of the power source.
Timing Intervals A general term used to describe that portion of time given to the
green, yellow, red, passage, etc. of a traffic controller.
Timing Plan The complete timing program for a signalized traffic intersection.
TOD Time of Day.
Tone An audio frequency signal.
Total Harmonic Distortion
(THD)
THD is the ratio of the root-mean-square (rms) value of the
harmonics to the amplitude of the fundamental component of the
ac waveform.
Page -76-
TOY Time of Year.
Traffic Actuated A type of traffic control signal in which the intervals are varied in
accordance with the demands of traffic as registered by the
actuations of detectors.
Traffic Actuated
Controller Assembly
A controller assembly for supervising the operation of traffic
control signals in accordance with the varying demands of traffic
as registered with the controller by detectors.
Traffic Adjusted Term used in master supervisory systems where vehicle
actuations and other data are fed to the master for effecting
signalization changes at several intersections rather than at each
intersection independently.
Traffic Adjusted System A system in which an analog computer controls cycle length at
special local controllers. Changes are based on threshold levels as
sensed by vehicle controllers.
Traffic Button An object extending above the roadway surface for the purpose of
channelizing traffic movement.
Traffic Control Signal A device by which traffic is alternately assigned the right-of-way
to the various movements at an intersection or other roadway
location.
Traffic Counter A device (usually portable) used to register the passage of
vehicles on a counting mechanism, giving one count for each
vehicle.
Traffic Detector A device by which vehicles, street cars, trolley buses, or
pedestrians are enabled to register their presence with a traffic
actuated controller.
Traffic Lane A strip of roadway intended to accommodate the forward
movement of a single line of vehicles.
Traffic Markings All lines, patterns, words or other devices except signs, set into
the surface of, applied upon or attached to the pavement or
curbing or to objects within or adjacent to the roadway, officially
placed for the purpose of regulating, warning or guiding traffic.
Traffic Phase Those right-of-way, change and clearance intervals in a cycle
assigned to any independent movement(s) of traffic.
Traffic Responsive Signal See Fully Actuated or Semi-Actuated signal.
Traffic Responsive
System
A system in which a master controller (analog or digital) specifies
cycle and offset based on the real time demands of traffic as
sensed by vehicle detectors.
Traffic Signal Mast Arm A structural support over the roadway, extending from a pole for
the purpose of supporting the signal head(s).
Page -77-
Traffic Signs A device mounted on a fixed or portable support whereby a
specific message is conveyed by means of words or symbols,
officially erected for the purpose of regulating, warning or
guiding traffic.
Trailing Car The vehicle behind the last car upon which gap-out expired in a
density controller. Gap-out occurs because the time headway
between the last car and trailing car exceeds the allowable gap
imposed by the controller.
Train Approach Signal A highway traffic signal which indicates to highway traffic the
approach and passage of railroad trains at a railroad highway
grade crossing.
Transceiver A communications device used to transmit and receive
information. A transmitter and receiver on a common chassis.
Transducer A sensor which transmits energy to the detection zone and
interprets the signal received from the detection zone. A device
that is actuated by power from one system and supplies power
usually in another form to a second system.
Transfer Rate The speed at which data may be read from or written to the
device.
Transition The process whereby the computer and the local intersection
controllers change from one program to another.
Transmission Line See Lead In Cable.
Transmitter That portion of a detector which transmits energy to a sensor.
Transyt An off line traffic signal grid optimization program developed in
England.
Truss Type Mast Arm A mast arm consisting of an assemblage of members forming a
rigid framework in the vertical plane.
TTR (Time To Reduce) During the process of Gap Reduction, it is the total time period
for the reduction process to take place.
Tube Type Mast Arm A mast arm consisting of a single tubular member.
Tubular Bracket Arm A signal bracket, for bracket mount applications, of tubular
construction through which wiring can be passed to provide
electrical connection of the signal faces supported by the bracket.
Tubular Spreader A signal bracket having tubular arms radiating from a hub
through which wiring can be passed to provide electrical
interconnection of the signal faces supported by the signal
bracket.
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TW The UL designation for thermoplastic insulated wire for use in
conduit and underground and wet locations. It is a common
building wire having a soft copper conductor, which may be
either solid or stranded.
Twisted Pair Two insulated conductors twisted together and coded.
Two Coil Magnetic
Detector
This describes a magnetic detector with two coils. This detector is
capable of serving as a directional detector.
TXD Transmit Data.
Type 170 (179) Controller One of the two major types of traffic signal controllers. Hardware
is standardized with the actual control being provided by
specialized software.
U
UL Underwriter’s Laboratories, Inc., is chartered as a non-profit
organization to maintain and operate laboratories for the
examination and testing of devices, systems and materials relative
to life, fire and casualty, hazards, and crime prevention.
UL Approved A product that has been tested and approved to Underwriter’s
Laboratories standards.
Ultrasonic Detector Ultrasonic detectors use the same principle as the microwave
detectors. A transducer transmits a beam of energy into an area
and receives a reflected beam from a vehicle. The sonic detector
transmits pulses of ultrasonic energy (20 to 50 kHz at 20 to 25
times/sec) through a transducer. The passage of a vehicle causes a
beam to be reflected to the transducer at a different frequency.
The transducer senses the change in frequency and converts it to
electrical energy. This energy is relayed to a transceiver, which
then sends an impulse to the controller unit to denote passage of a
vehicle.
Unconditioned Line A voice grade private line data channel (such as the 3002 type
channel) without compensation to minimize attenuation in the
audio frequency bank. See Voice Grade Line.
Upstream The roadway portion of an intersection which precedes the stop
line.
V
Vacuum Tube An electronic tube having its components encased and evacuated
to a high degree of vacuum, used primarily in timing circuits and
power supplies in electronic controllers, and as amplifiers in
detector circuits.
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Variable Initial A feature which allows the minimum green period to be extended
depending on the size of the waiting vehicle queue. See Seconds
per Actuation (S/A), Maximum Variable Initial, and Volume
Density.
Variable Initial Interval A controller design feature which adjusts the duration of initial
interval for the number of vehicles in the queue.
Vehicle Call The registration of a demand for right-of-way by traffic vehicles
to the controller timer.
Vehicle Detector Activation of this signal shall cause the controller to register a
vehicle call for the programmed phase.
Vehicle Detector System A system for indicating the presence or passage of vehicles. See
Detector System.
Vehicle Recall A locked call will be placed on an active phase automatically
when leaving green.
Vehicle Standard A test unit that produces a change in the loop inductance
equivalent to a conventional American Sedan.
Vehicular Phase A vehicular phase is a phase which is allocated to vehicular traffic
movement as timed by the controller unit.
Veiling (shielding) Regulating the light from a signal by mechanical or optical means
to restrict the visibility from a desired portion of the roadway.
Vibrotactile Pedestrian
Device
A device that communicates, by touch, information about
pedestrian timing using a vibrating surface.
Video Imaging Detector
System (VIDS)
A detection system that analyzes a video image of an approach
and by pattern matching identifies and classifies vehicles in that
approach. See also Wide Area Detection System.
Visibility Limited Signal
Face or Signal Section
A type of signal face or signal section designed to restrict the
visibility of a signal indication from the side, to a certain lane or
lanes, or to a certain distance from the stop line.
Visor (Hood) The part of a signal section which protects the lens face from
direct ambient light and screens the indication from traffic not
intended to view it.
Voice Grade Lines A channel suitable for transmission of speech, digital, analog, or
facsimile data, generally in the frequency range of 300 to 3000
Hz.
Volatile Memory A storage medium in which information is destroyed when power
is removed from the system.
Volt-Amperes The product of root-mean-square (rms) line voltage and rms line
current measured with true rms meter.
Voltage Monitor
(NEMA) controller
This output shall indicate that the power supplied to the internal
logic of the controller is within specified limits.
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Voltage Monitor
Indicators (NEMA)
CVM / Watchdog, 24V-1, 24V-2. One or more of these indicators
will be illuminated, on the conflict monitor, if the corresponding
voltage input is below the minimum specified level. If the
Voltage Monitor Latch (VM LATCH) option is enabled and the
unit is triggered by a improper voltage condition, the
corresponding indicator(s) will remain illuminated until the unit
receives a reset command from the manual reset or external reset
input.
Voltage Monitor Latch
(NEMA)
When the Voltage Monitor Fault Latch option is enabled by the
front panel switch, the absence of the proper voltage level, at
either CVM input or the two 24VDC inputs (24V-1 & 24V-2),
will place the conflict monitor into a fault mode, the
corresponding indicator(s) will remain illuminated until the unit
receives a reset command from the manual reset or external reset
input.
Volume The quantity in units of traffic.
Volume Density A process used with detectors located at, or at sufficient distance
in advance of, the intersection which makes use of vehicle
actuation quantities and time-of-waiting of the vehicles to vary
green interval portions for increased capacity and minimized
delays.
Volume Density
Controller
An actuated controller which, in its two phase model, has three
gap reduction factors, (namely, Time Waiting, Cars Waiting, and
Density), based on opposing phase vehicle time waiting.
Volume Extension Mode A manner of operation of a multiple detector design in which the
green is extended by heavy traffic operating at a speed below the
Design Speed. The speed is so slow that the extension is
attributable to the heavy volume.
W
W4IKS Actuated 170 Local Software Program (Wapiti Micro Systems
Corp’s).
W7OSM 170 On Street Master Software Program (Wapiti Micro Systems
Corp’s).
W9FT Fixed Time 170 Local Software Program (Wapiti Micro Systems
Corp’s).
Walk “2" An additional walk time called into effect by Time Of Day or Day
Of Week.
Walk Interval An interval during which the WALKING PERSON (symbolizing
WALK) signal indication is displayed. When a verbal message is
provided at an accessible pedestrian signal, the verbal message is
“walk sign.”
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Walk Rest Modifier This input when true shall modify non-actuated operation only.
With this input active, non-actuated phases shall remain in the
timed out WALK state (rest in WALK) in the absence of a
serviceable conflicting call without regard to the HOLD input
status. If this input is active, the controller unit shall recycle the
pedestrian movement when reaching state DON’T WALK in the
absence of a serviceable conflicting call. With this input non-
active (normal state) non-actuated phases shall not remain in the
timed out WALK state unless the HOLD input is active.
Warning, Advance See Advanced Warning.
Warning Beacon A beacon used only to supplement an appropriate warning or
regulatory sign or marker.
Warrants The results of actual surveys made at an intersection to determine
if signalization is needed or requires change. Refer to Uniform
Manual for suggested methods and determining factors.
Watch Dog This optional "Flashing Logic" output, from the cabinet controller
circuitry, is monitored by the conflict monitor it reports the health
of the control unit. The cabinet controller should toggle the
watchdog output’s logic state once every 100msec.
Watch Dog Timer Timing device designed to detect faults due to lack of response
from a remote controlled machine.
Water Blocked Impervious to water entrance and migrations as a water blocked
lead-in cable or water blocked splices.
Week Program A program used to determine the time of operation according to a
weekly schedule which may be preset to vary from day to day.
Weekly Programmer A device used to determine the time of operation of programs on
traffic control equipment according to a weekly schedule which
may be preset to vary from day to day.
Weigh In Motion (WIM) A system of detectors and weighing devices that weigh vehicles
while they are in motion over the detectors.
Weighted Sensor Data Information received from a detector which has been adjusted
according to a preset value. For example, the information
received from a detected lane is adjusted to reflect traffic on
adjacent, undetected lanes as well.
Wide Area Detector
System (WADS)
Video interpretation to provide detection over a wide area of an
approach. A micro-processor evaluates a video image of the
approach to determine the presence of vehicles. Later
developments are referred to as VIDS.
Wire Gauge See AWG.
X
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XHHW Cross-linked Polyethylene insulated wire, rated at 90 degree
Celsius in dry, and 75 degree Celsius in wet locations.
Y
Yellow Change Interval The first interval following the green right-of-way interval in
which the signal indication for that phase is yellow.
Yellow Clearance See Yellow Change Interval.
Yellow Lock Locks in vehicle call placed on phase anytime phase is not green.
Yellow-Red Flash
Terminals
Terminals which are wired to give the operation of flashing either
yellow or red on each traffic signal face by rearranging jumpers
and or field wires.
Yield The action of allowing a semi-actuated controller, or an actuated
controller operation in the semi-actuated mode, to terminate the
main street phase to begin satisfying existing cross street
demands. Also see Hold.
Yield Point The earliest point at which the coordinated phase may end to give
right of way to one or more of the opposing phases.
Related to permissive period but more specifically a point in the
cycle of a coordination system where the opposing phases are
permitted to give right-of-way to one or more of the opposing
phases.
Z
ZM Zone Master
Zone Detection See Detection Zone.
Zone of Detection That area of the roadway within which a vehicle is to be detected
by a vehicle detector system.
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Compiled from:
Report Number FHWA-IP-90-002 (July 1990)
Report Number FHWA-SA-93-061 (July 1993)
Report Number FHWA/TX-95/1255-2F (August 1995)
Manual of Traffic Signal Design (James Kell)
NEMA TS-1 Standards 1983
Multisonics 911 Controller Manual
Inspector’s Manual for Traffic Signal Construction (August, 1985)
Traffic Signal Manual (IMSA)
ITE Specification for LED signal heads
MUTCD manual, (chapter 4)
DRS nema class terms and definitions
ODOT’s Construction guideline manual for Traffic Control Devices
Oasis User’s Manual
W4IKS User’s Manual
W7OSM User’s Manual
EDI documentation, SSM-6E/12E Conflict Voltage Monitor
Crouse-Hinds DM series digital controller units
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