Chapter 4A. General
Section 4A.01 Types
Support:
The following types and uses of highway traffic signals are discussed
in Part 4: traffic control signals; pedestrian signals; emergency-vehicle
traffic control signals; traffic control signals for one-lane, two-way
facilities; traffic control signals for freeway entrance ramps;
traffic control signals for movable bridges; lane-use control signals;
flashing beacons; and in-roadway lights.
Section 4A.02 Definitions
Relating to Highway Traffic Signals
Standard:
The following technical terms, when used in Part 4, shall be defined
as follows:
- Accessible Pedestrian Signal—a device that communicates
information about pedestrian timing in nonvisual format such
as audible tones, verbal messages, and/or vibrating surfaces.
- 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-rail grade crossings or highway-light
rail transit grade crossings.
- Actuated Operation—a type of traffic control signal
operation in which some or all signal phases are operated on
the basis of actuation.
- Actuation—initiation of a change in or extension of
a traffic signal phase through the operation of any type of
detector.
- Approach—all lanes of traffic moving towards an intersection
or a midblock location from one direction, including any adjacent
parking lane(s).
- Average Day—a day representing traffic volumes normally
and repeatedly found at a location, typically a weekday when
volumes are influenced by employment or a weekend day when volumes
are influenced by entertainment or recreation.
- Backplate—see Signal Backplate.
- Beacon—a highway traffic signal with one or more signal
sections that operates in a flashing mode.
- Conflict Monitor—a device used to detect and respond
to improper or conflicting signal indications and improper operating
voltages in a traffic controller assembly.
- Controller Assembly—a complete electrical device mounted
in a cabinet for controlling the operation of a highway traffic
signal.
- Controller Unit—that part of a controller assembly
that is devoted to the selection and timing of the display of
signal indications.
- 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, and in the absence of a sidewalk on one side of the
roadway, the part of a roadway included within the extension
of the lateral lines of the sidewalk at right angles to the
centerline; (b) any portion of a roadway at an intersection
or elsewhere distinctly indicated as a pedestrian crossing by
lines on the surface, which may be supplemented by a contrasting
pavement texture, style, or color.
- Cycle Length—the time required for one complete sequence
of signal indications.
- 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.)
- Detector—a device used for determining the presence
or passage of vehicles or pedestrians.
- Dual-Arrow Signal Section—a type of signal section
designed to include both a yellow arrow and a green arrow.
- Emergency Vehicle Traffic Control Signal—a special
traffic control signal that assigns the right-of-way to an authorized
emergency vehicle.
- Flasher—a device used to turn highway traffic signal
indications on and off at a repetitive rate of approximately
once per second.
- Flashing—an operation in which a highway traffic signal
indication is turned on and off repetitively.
- Flashing Mode—a mode of operation in which at least
one traffic signal indication in each vehicular signal face
of a highway traffic signal is turned on and off repetitively.
- Full-Actuated Operation—a type of traffic control signal
operation in which all signal phases function on the basis of
actuation.
- Highway Traffic Signal—a power-operated traffic control
device by which traffic is warned or directed to take some specific
action. These devices do not include signals at toll plazas,
power-operated signs, illuminated pavement markers, warning
lights (see Section
6F.78), or steady-burning electric lamps.
- 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
users to slow down and/or come to a stop.
- Intersection—(a) the area embraced within the prolongation
or connection of the lateral curb lines, or if none, the lateral
boundary lines of the roadways of two highways that join one
another at, or approximately at, right angles, or the area within
which vehicles traveling on different highways that join at
any other angle might come into conflict; (b) the junction of
an alley or driveway with a roadway or highway shall not constitute
an intersection.
- Intersection Control Beacon—a beacon used only at an
intersection to control two or more directions of travel.
- Interval—the part of a signal cycle during which signal
indications do not change.
- Interval Sequence—the order of appearance of signal
indications during successive intervals of a signal cycle.
- Lane-Use Control Signal—a signal face displaying signal
indications to permit or prohibit the use of specific lanes
of a roadway or to indicate the impending prohibition of such
use.
- Lens—see Signal Lens.
- Louver—see Signal Louver.
- Major Street—the street normally carrying the higher
volume of vehicular traffic.
- Malfunction Management Unit—same as Conflict Monitor.
- Minor Street—the street normally carrying the lower
volume of vehicular traffic.
- 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 Signal—a highway traffic signal installed
at a movable bridge to notify traffic to stop during periods
when the roadway is closed to allow the bridge to open.
- Movable Bridge Warning Gate—a type of traffic gate
designed to warn, but not primarily to block, vehicle and/or
pedestrian traffic when placed in the appropriate position.
- Pedestrian Change Interval—an interval during which
the flashing UPRAISED HAND (symbolizing DONT WALK) signal indication
is displayed. When a verbal message is provided at an accessible
pedestrian signal, the verbal message is "wait."
- Pedestrian Clearance Time—the time provided for a pedestrian
crossing in a crosswalk, after leaving the curb or shoulder,
to travel to the far side of the traveled way or to a median.
- Pedestrian Signal Head—a signal head, which contains
the symbols WALKING PERSON (symbolizing WALK) and UPRAISED HAND
(symbolizing DONT WALK), that is installed to direct pedestrian
traffic at a traffic control signal.
- Permissive Mode—a mode of traffic control signal operation
in which, when a CIRCULAR GREEN signal indication is displayed,
left or right turns are permitted to be made after yielding
to pedestrians and/or oncoming traffic.
- Platoon—a group of vehicles or pedestrians traveling
together as a group, either voluntarily or involuntarily, because
of traffic signal controls, geometrics, or other factors.
- Preemption Control—the transfer of normal operation
of a traffic control signal to a special control mode of operation.
- Pretimed Operation—a type of traffic control signal
operation in which none of the signal phases function on the
basis of actuation.
- Priority Control—a means by which the assignment of
right-of-way is obtained or modified.
- Protected Mode—a mode of traffic control signal operation
in which left or right turns are permitted to be made when a
left or right GREEN ARROW signal indication is displayed.
- 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.
- 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.
- Red Clearance Interval—an optional interval that follows
a yellow change interval and precedes the next conflicting green
interval.
- Right-of-Way (Assignment)—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.
- Roadway Network—a geographical arrangement of intersecting
roadways.
- Semiactuated Operation—a type of traffic control signal
operation in which at least one, but not all, signal phases
function on the basis of actuation.
- Separate Left-Turn Signal Face—a signal face for controlling
a left-turn movement that sometimes displays a different color
of circular signal indication than the adjacent through signal
faces display.
- Shared Left-Turn Signal Face—a signal face, for controlling
both a left turn movement and the adjacent through movement,
that always displays the same color of circular signal indication
that the adjacent through signal face or faces display.
- Signal Backplate—a thin strip of material that extends
outward from and parallel to a signal face on all sides of a
signal housing to provide a background for improved visibility
of the signal indications.
- Signal Coordination—the establishment of timed relationships
between adjacent traffic control signals.
- Signal Face—that part of a traffic control signal provided
for controlling one or more traffic movements on a single approach.
- Signal Head—an assembly of one or more signal sections.
- Signal Housing—that part of a signal section that protects
the light source and other required components.
- Signal Indication—the illumination of a signal lens
or equivalent device.
- Signal Lens—that part of the signal section that redirects
the light coming directly from the light source and its reflector,
if any.
- Signal Louver—a device that can be mounted inside a
signal visor to restrict visibility of a signal indication from
the side or to limit the visibility of the signal indication
to a certain lane or lanes, or to a certain distance from the
stop line.
- 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 assembly of a signal housing, signal
lens, and light source with necessary components to be used
for providing one signal indication.
- Signal System—two or more traffic control signals operating
in signal 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 direct 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.
- Speed Limit Sign Beacon—a beacon used to supplement
a SPEED LIMIT sign.
- Steady (Steady Mode)—the continuous illumination of
a signal indication for the duration of an interval, signal
phase, or consecutive signal phases.
- Stop Beacon—a beacon used to supplement a STOP sign,
a DO NOT ENTER sign, or a WRONG WAY sign.
- Traffic Control Signal (Traffic Signal)—any highway
traffic signal by which traffic is alternately directed to stop
and permitted to proceed.
- Vibrotactile Pedestrian Device—a device that communicates,
by touch, information about pedestrian timing using a vibrating
surface.
- Visibility-Limited Signal Face or Signal Section—a
type of signal face or signal section designed (or shielded,
hooded, or louvered) 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.
- 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."
- Warning Beacon—a beacon used only to supplement an
appropriate warning or regulatory sign or marker.
- Yellow Change Interval—the first interval following
the green interval during which the yellow signal indication
is displayed.
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