Glossary
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
Abbreviations | Traffic Operations Manual
A
Activity - The protected work area of a vehicle-related roadway incident that is shielded by the block from apparatus and other emergency vehicles.
Adaptation – Process by which the visual system becomes accustomed to different light intensity or different light colors than it was exposed to previously. It results in a change in the sensitivity of the eye to light.
Advance Warning - Notification procedures that advise approaching motorists to transition from normal driving status to that required by the temporary emergency traffic control measures ahead of them.
Ambient Lighting – General lighting used to provide visibility in a built environment. Ambient lighting includes both artificial and natural lighting and does not include task lighting and accent lighting.
Arterial – See Roadway Classification – Major
Average Daily Traffic (ADT) – The average calculated for up to five years after the roadway is opened to traffic.
Ballast – Device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current, and waveform) for starting and operating.
Bicycle Path - Facilities for the exclusive use of bicyclists and pedestrians with cross flows by vehicles minimized.
Bicycle Ramp – Allows bicyclists to exit and enter the roadway in advance of the circulatory roadway. Roundabouts usually incorporate bicycle facilities.
Bicyclist Overcrossing or Undercrossing – Facility that provides a connection between bikeways or roads open to bicyclists.
Bikeway – Any road, street, path, or way that in some manner is specifically designated as being open to bicycle travel, regardless of whether such facilities are designated for the exclusive use of bicycles or are to be shared with other transportation modes.
Block - Positioning a response vehicle (typically a fire engine) on an angle to the lanes of traffic creating a physical barrier between upstream traffic and the work area. Includes 'block to the right' or 'block to the left.'
Brightness – See luminance and subjective brightness.
Buffer Strip – Area between the circulatory roadway and the sidewalk that separates vehicles and pedestrians and helps guide pedestrians to designated crossing locations.
Buffer Zone - The space between personnel and vehicles in the protected work zone and nearby moving traffic.
C
Calculation Point Spacing – Distance between points where vertical illuminance levels are calculated in lighting software.
Center Island – The center of a roundabout around which traffic circulates. The center island does not necessarily need to be circular.
Circulatory Roadway – The path vehicles use to travel counterclockwise around the center island of a roundabout.
Clear Recovery Zone – Unobstructed, relatively flat area provided beyond the traveled way to permit the recovery of cars that accidentally run off the road.
Conflict – Occurs when the paths followed by traffic diverge, merge, or cross.
Conflict Area – Area of a roadway where the motorist's special attention is required to interpret the functional features (e.g., bullnose) and/or activities (e.g., pedestrians, turning vehicles, railroad grade crossing) of the roadway, to decide on their driving routine. It is that area which encompasses all the conflict points.
Continuous Lighting – Lighting system designed to provide a uniform level of illuminance throughout a specified section of roadway.
Contrast – See luminance contrast.
Conventional Highway – Highway without control of access that may or may not be divided. Grade separations at intersections or access control may be used when justified at spot locations.
Correlated Color Temperature (CCT) – Unlike the color rendering index (CRI), which describes how faithfully a light source represents other objects, the correlated color temperature (CCT) describes the color output of the lamp itself. Some common CCT values include:
- 2700K to 3000K, with a warm tinge of yellow that creates appealing and relaxing environments.
- 4000K, a neutral white tone that strikes just the right balance between relaxation and concentration.
- 6500K, with a slight tinge of blue, which has an energizing effect.
Although the correct technical term is correlated color temperature, it is often shortened to only color temperature. It is also important to note that the CCT is not the real operating temperature of a lamp; it is the temperature to which you would have to heat a black body to make it glow with the same color. For example, an LED bulb with a CCT of 5000K glows in the same color as a black body heated to a real temperature of 5000K, but the LED bulb itself does not reach that temperature.
Crosswalk – Area designated by markings for pedestrians to cross the roadway.
D
Darkness – Any time from one-half hour after sunset to one-half hour before sunrise and any other time when visibility is not sufficient to render clearly discernible any person or vehicle on the highway at a distance 1,000 feet.
Discomfort Glare – Glare producing discomfort. It does not necessarily interfere with visual performance or visibility.
Downstream - The direction that traffic is moving as it travels away from the incident scene.
E
Expressway – Highway with partial control of access that may or may not be divided or have grade separations at intersections.
F
Fend-off Position - The location of the fire truck that is placed at a 30-degree angle to the road to deflect any errant vehicles that might strike the fire truck accidently.
Footcandle, fc – Unit of illuminance when a foot is taken as the unit of length. It is the illuminance on a surface that is one square foot in area, on which there is a uniformly distributed flux of one lumen. Or it is the illuminance produced on a surface of all points that are one foot from a directionally uniform point source of one candela.
Freeway – A divided arterial highway with full control of access and with grade separations at intersections.
G
Glare – Sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort, or loss in visual performance and visibility. Visual impairment caused by a bright source of light, directly visible or reflected by a surface. There are two types of glares:
- Discomfort glare causes an instinctive reaction to close the eyes and look away. This is the type of glare felt when exposed to a potent HID light or when the sun is directly visible through a window.
- Disability glare impairs vision but does not cause the same reaction as discomfort glare. If a light source gets reflected on your laptop screen, for example, it does not bother your eyes but distinguishing objects on the screen may be impossible.
H
Headway - The amount of time between two transit vehicle arrivals at a stop.
High Mast Lighting – Illumination of a large area by means of a group of luminaires that are designed to be mounted in fixed orientation at the top of a high support or pole (generally 20 meters or higher).
High-Intensity Discharge (HID) – Type of lighting often used for industrial and outdoor settings due to its powerful output. Some examples of HID lighting are mercury-vapor, metal-halide, xenon, high-pressure sodium, and low-pressure sodium lamps.
High-Pressure Sodium (HPS) – Subtype of HID lighting where excited sodium vapor is the source of light. The lighting output of HPS lamps is characterized by its warm yellow hue and are commonly used in cobra-head streetlights.
Highway – A public right of way for the purpose of travel or transportation, as defined in the Caltrans Highway Design Manual.
I
Illuminance – Density of luminous flux incident on a surface, measured in footcandles, or fc (or lux, lx). One footcandle is the illumination of a surface one square foot in area on which there is a uniformly distributed luminous flux of one lumen. One footcandle is 10.76 lux. The illuminance requirements of built environments are determined by their intended purpose, and there are two common units of measurement:
- Lux - Equivalent to one lumen per square meter.
- Footcandle - Equivalent to one lumen per square foot.
Higher illuminance levels make surfaces appear brighter to the human eye and improve visibility.
Illuminating Engineering Society of North America (IESNA) – Technical authority in the lighting industry, with dozens of publications to its credit. IESNA has members and recognition throughout the world.
Incident - FHWA has defined an incident as: "Any non-recurring event that causes a reduction of roadway capacity of an abnormal increase in demand."
Incident (Reportable) - CHP and Caltrans have defined a reportable incident as: "An unplanned non-recurring event that reduces highway capacity that requires both agencies to respond to the incident scene."
Incident Clearance Time - The interval defined as the time between the first recordable awareness of the incident and the time at which the last responder has left the scene.
Incident Commander - the incident commander has overall responsibility for managing the entire incident. Specifically, for ensuring incident safety, providing information services to internal and external stakeholders, and establishing and maintaining liaison with other agencies participating in the incident.
Interchange –Road junction that uses grade separation, and typically one or more ramps, to permit traffic on at least one highway to pass through the junction without interruption from other crossing traffic streams.
Intersection – General area where two or more roadways (highways) join or cross, including the roadway and roadside facilities for traffic movement within it.
Isolated Interchange – Separated roadway crossing with one or more ramp connections between the crossing roadways, which is illuminated and is not part of a continuous roadway system.
Isolated Intersection – Area in which two or more non-continuously illuminated roadways join or cross.
J
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K
Kelvin (K) – Measurement unit for temperature, although in the lighting industry it is more commonly used to indicate the CCT of light sources.
Kilowatt (kW) – Measurement unit for electric power, equivalent to 1000 watts; thus, a 10kW light = 10,000 watts. This term should not be confused with kilowatt-hour. See watt.
Kilowatt-Hour (kWh) – Measurement unit for energy consumption. As implied by its name, it is equivalent to the amount of energy consumed by a one-kilowatt appliance running for one hour. Electric utility bills are often calculated based on kilowatt-hour consumption per month. This term should not be confused with kilowatt.
L
L70: Extrapolated life in hours of the luminaire when the luminous output depreciates 30 percent from the initial values.
Lamp – A generic term for an artificial source of light.
Lateral – Across the roadway (perpendicular to the travel lane).
Lateral Buffer Zone - Created when the front bumper of the fire truck is positioned at least 2 feet from the longitudinal pavement marking line. Designed to reduce encroachment into designated traffic lanes.
LED (Light-Emitting Diode) – Solid-state component that emits light when exposed to electric current. LED lighting represents the state-of-the-art in the industry, outclassing most other types of lighting in terms of energy efficiency, design flexibility, and colors of light available.
Light – Visually evaluated radiant energy.
Light Loss Factor (LLF) – Multiplier used to predict performance (maintained illuminance) based on the initial rated output of a luminaire. Typically, a 0.9 LLF is used for SHS lighting analysis.
Lighting Standard – Pole and mast arm supporting the luminaire.
Longitudinal –Along the direction of travel of the roadway (parallel to the travel lane).
Lumen – Measurement unit for the lighting output of lamps or fixtures. The total lumens emitted, and their spatial distribution are of paramount importance when creating appealing and luxurious indoor spaces. In lighting, lumens can be compared to miles traveled and watts can be compared to fuel consumption. Radiometrically, it is determined from the radiant power.
Photometrically, it is the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela.
Luminaire –Includes the lamp, the ballast or driver, internal wiring, reflectors, lens, and any additional components required to deliver light. A complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and to connect the lamps to the power supply. Sometimes includes ballasts and photocells.
Assembly that houses the light source and controls the light emitted from the light source.
Luminaire Spacing – Distance between successive luminaires along the roadway, walkway, or bikeway.
Luminance (Photometric Brightness) –Quantity of luminous flux emitted, reflected, or transmitted from a surface in a direction, measured in cd/feet2
or cd/m2. This is the property of light we can visibly see with our eyes.
Luminance, L (cd/m2) – Quotient of the luminous flux at an element of the surface surrounding the point and propagated in directions defined by an elementary cone containing the given direction, by the product of the solid angle of the cone and area of the orthogonal projection of the element of the surface on a plane perpendicular to the given direction. The luminous flux may be leaving, passing through, and/or arriving at the surface. Note: In common usage the term "brightness" usually refers to the strength of sensation which results from viewing surfaces or spaces from which light comes to the eye. This sensation is determined in part by the measurable luminance defined above and in part by conditions of observation such as the state of adaptation of the eye.
Luminous Flux – Luminous flux is the measure of the total amount of energy radiated per second from a light source in all directions. It is measured in lumens. One lumen is defined as the luminous flux of the uniform point light source having a luminous intensity of 1 candela.
Luminous Flux Density at a Surface – Luminous flux per unit area at a point on a surface. Note: this need not be a physical surface; it may be a mathematical plane.
Luminous Intensity – Lighting emission in a specific direction, measured in candelas. Luminous intensity changes depending on the viewing angle. Not to be confused with luminous flux.
Lux – SI unit for illuminance, or lumens per unit of area. One lux is equivalent to one lumen per square meter. A key component of lighting design is achieving a suitable illuminance level depending on the application. It is the illuminance on a surface one square meter in area on which there is a uniformly distributed flux of one lumen, or the illuminance produced at a surface all points that are at one meter from a uniform point source of one candela. Conversion Formula: fc x 10.8 = Lux.
M
Mercury Lamp – Subtype of HID lamp that produces its lighting output by stimulating mercury vapor, hence its name. Mercury lamps may use a phosphor coating to enhance lighting performance and are commonly used in outdoor and industrial lighting applications.
Mounting Height – Vertical distance between the roadway surface and the center of the apparent light source of the luminaire.
N
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O
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P
Pedestrian and Bicycle Overcrossings – A facility that provides a connection between pedestrian walkways/bikeways or roads open to pedestrian walkways/bicycling.
Pedestrian Classification:
- High (≥ 100) – Areas with significant numbers of pedestrians expected to be on the sidewalks or crossing the streets during darkness. Examples are downtown retail areas, near theaters, concert halls, stadiums, and transit terminals.
- Medium (11 to 99) – Areas where lesser numbers of pedestrians use the streets at night. Typical are downtown office areas with libraries, apartments, neighborhood shopping, industrial, older city areas, and streets with transit lines.
- Low (10 ≤) – Areas with very low volumes of night pedestrian usage. These can occur in any of the cited roadway classifications but may be typified by suburban single-family streets, very low- density residential developments, and rural or semi-rural areas.
Pedestrian Overcrossing or Undercrossing – Facility that provides a connection between pedestrian walkways.
Pedestrian Path – Paved walkway along the side of the street that is specifically designed for walking. It is a facility that is physically separated from the roadway and intended for pedestrian use.
Pull Box – Box with a cover that is installed in an accessible place in a conduit run to facilitate pulling in wires or cables.
Q
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R
Roadway Classification:
- Major (≥ 3,500 ADT) – Roadway that serves as the principal network for through-traffic flow. They connect areas of principle traffic generation and important rural roadways entering and leaving the city. They are often known as arterials, throughfares, or peripherals.
- Collector (1,501 to 3,499 ADT) – Roadway that serves traffic between major and local streets. It may be used for truck or bus movement and give direct service to abutting properties. It does not handle long, through trips.
- Local (100 to 1,500 ADT) – Roadway that primary provides direct access to residential, commercial, industrial, or other abutting property. They make up a large percentage of the total street system but carry a small proportion of vehicular traffic.
Roadway Clearance Time - The interval between the first recordable awareness of an incident (detection, notification, or verification) by a responding agency and the first confirmation that all lanes are available for traffic flow.
S
Safe-Positioning - The positioning of emergency vehicles at an incident in a manner that attempts to protect both the responders performing their duties and road users traveling through the incident scene, while minimizing, to the extent practical, disruption of the adjacent traffic flow.
Secondary Incidents - Unplanned incidents beginning with the time of detection of the primary incident where a collision occurs either a) within the incident scene or b) within the queue, including the opposite direction, resulting from the original incident.
Splitter Island – Area on an approach that separates entering traffic from exiting traffic.
State Highway System (SHS) – Network of highways that are owned and maintained by the California Department of Transportation.
Subjective Brightness – Subjective attribute of any light sensation given rise to the perception of luminous intensity, including the whole scale of qualities of being bright, lightness, brilliant, dim, or dark.
Surface Street – Street that is not a freeway and has at-grade intersections with other surface streets.
T
Taper - The action of merging several lanes of moving traffic into fewer moving lanes.
Temporary Traffic Control Zone - An area of a highway within which emergency personnel perform their fire, EMS, and rescue takes at a vehicle-related incident, where road user conditions are changed by the use of temporary traffic control devices, flaggers, uniformed law enforcement officers, or other authorized personnel.
Transition Zone - The lanes of a roadway within which approaching motorists change their speed and position to comply with the traffic control measures established at an incident scene.
Truck Apron – Portion of an island or exterior portion along the traveled way that is raised above the travel lanes but traversable by large vehicles.
Tunnel – As defined by the American Association of State Highway and Transportation Officials (AASHTO) Technical Committee for Tunnels (T-20) are enclosed roadways with vehicle access that is restricted to portals regardless of the structure type or construction method. The committee further defines road tunnels not to include enclosed roadways created by highway bridges, railroad bridges, or other bridges. This definition applies to all types of tunnel structures and tunnels, mined and bored tunnels in rock and soft ground, and immersed tunnels.
U
Upstream - The direction that traffic is traveling from as the vehicle approaches the incident sence.
V
Visibility – Quality or state of being perceivable by the eye. In many outdoor applications, visibility is sometimes defined in terms of the distance at which an object can be just perceived by the eye. In indoor and outdoor applications, it is usually defined in terms of the contrast or size of a standard test object, observed under standardized viewing conditions, having the same threshold as the given object.
W
Walkway – Passage or path for walking such as a sidewalk or pedestrian path.
Warrant – Threshold condition based upon average or normal conditions that, if found to be satisfied as part of an engineering study, must result in analysis of other traffic conditions or factors to determine whether a traffic control device or other improvement is justified. Warrants are not a substitute for engineering judgment. The fact that a warrant for a traffic control device is met is not conclusive justification for the installation of the device.
Watt – Measurement unit for the electric power consumption of lighting fixtures, or any other appliance that runs with electricity. In lighting, lumens can be compared to miles traveled and watts can be compared to fuel consumption.
X
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Y
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Z
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