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Terms that are in use on this site.

There are 111 entries in this glossary.
All A B C D E F G H I L M O P R S T V W Z
Term Definition
AASHTO

American Association of State and Highway Transportation Officials - a nonprofit, nonpartisan association representing highway and transportation departments in the 50 states, the District of Columbia, and Puerto Rico. It represents all five transportation modes: air, highways, public transportation, rail ,and water. Its primary goal is to foster the development, operation, and maintenance of an integrated national transportation system.

ACCESS

The ability to enter or leave a residence, business, or parcel of land from a roadway by way of a connecting driveway.

ACCESS MANAGEMENT

Limiting the ability of traffic to enter, leave, or cross thoroughfares; regulating the spacing and design of driveways, medians, intersections, and traffic signals to promote the efficient flow of through traffic.

ACCESSIBILITY

The ability to reach destinations, activities, and services.

ADA

Americans with Disabilities Act - A set of guidelines passed in 1990 to assure a minimum level of accessibility to buildings and facilities for individuals with disabilities; Title III of the legislation deals with public accommodations.

ADT

Average Daily Traffic - The average number of vehicles passing a specific point on a roadway during 24 hour period.

AMENITY ZONE

A portion of the public right of way, typically adjacent to the sidewalk but outside the pedestrian walking area, including streetscape elements, landscaping, and street trees.  Amenity zones are more often seen in higher density, pedestrian-oriented areas such as retail or mixed-use developments.

APS

Accessible Pedestrian Signal - A device communicating information about pedestrian signal timing using a non-visual format, such as audible tones, verbal messages, or vibrating surfaces.

ARTERIAL

A controlled access highway designed for through traffic (longer trips, higher volume and speed); arterials are typically on a continuous route and are often divided; the right-of-way is usually 120 feet.

ARTICULATED BUSES

Buses with an “accordion” section in the middle allowing them to bend and flex; these buses have more passenger capacity than standard buses.

ARTICULATION

The division of a building façade into distinct sections; the materials, patterns, textures, and colors that add visual interest to a building or facade; areas with higher levels of articulation are typically more inviting pedestrian environments.

ATTACHED SIDEWALK

Sidewalk is immediately adjacent and attached to the street curb.

BACK-IN DIAGONAL PARKING

Increases the efficiency and number of on-street parking spaces; provides a more pedestrian and bicycle friendly design than traditional parallel parking.

BACKAGE ROAD

A local road, typically running parallel to a route with a higher functional classification, used to provide alternative access to properties.

BICYCLE DETECTOR

Sensors used to detect bicycles for traffic actuated signals at signalized intersections.

BICYCLE LANE

Portion of the street designated by striping, signing, or pavement markings for preferential or exclusive use by bicyclists.  Bike lanes are established with appropriate pavement markings and signing to delineate the right of way assigned to bicyclists and motorists, and to provide more predictable movements by each.  Bike lanes are usually paired one-way facilities located on both sides of streets with moderate to heavy traffic volumes.  Steeply sloped streets can have bike lanes on one side for climbing, while it may not be necessary to stripe lanes on the downhill side because bicycle speeds approach motor vehicles on these sections. The minimum width of a bike lane is 4 feet in most areas, or 5 feet when adjacent to on-street parking or if measured from the curb face.  Bicycle lane design at intersections must be treated carefully to minimize conflicts between bicycle and auto movements.

BIKE BOX

Designated, marked area at a signalized intersection that places bicycles at the front of the queue.  Bike boxes increase the visibility of bicyclists and allow them to enter/clear the intersection before motor vehicles.

BLOCK LENGTH

The longest dimension of a block, from one intersection to the next.  Shorter blocks create a denser network, which can help disperse traffic and create additional route choices for all modes.

BOULEVARD

A wide street, usually with a median or promenade, lined with trees.

BUFFER

Portion of the roadway between the curb or edge of the pavement and the sidewalk; used to separate pedestrians and vehicles.  Buffers often include landscaping, trees, or utility poles.

BULBOUT

An extension of the sidewalk or curb line into the parking lane to reduce the effective street width. Also known as curb bulb-outs or neckdowns, curb extensions significantly improve pedestrian crossings by reducing the pedestrian crossing distance, visually and physically narrowing the roadway, improving the ability of pedestrians and motorists to see each other, and reducing the time that pedestrians are in the street.  Curb extensions are only appropriate where there is an on-street parking lane. Curb extensions should not extend more than 6 feet from the curb, and must not extend into travel lanes, bicycle lanes or shoulders. The turning needs of larger vehicles, such as school buses, need to be considered in curb extension design.

CLEAR ZONE

The area adjacent to the street (measured from the edge of the travel lane) that is kept clear of major obstructions.

COG

Council of Governments - A group of local governments that voluntarily organizes and cooperates to create a more comprehensive, regional planning effort.

COLLECTOR

A two- to four-lane roadway providing mobility and access.  Collector streets can be found in residential neighborhoods, commercial and industrial areas, and central business districts.  Collectors usually have minimal access control, and the right-of-way is typically 80 feet.  Collectors are designed to move traffic from local roads to secondary arterials.

COLOR TEMPERATURE

A method used to characterize the spectral properties of a light source and specify the appropriate light source type in architectural design; light sources of the same color can vary in quality (CRI is used to describe light source quality); lower color temperatures are warmer (yellow/red) while high color temperatures are cooler (blue); the standard unit for color temperature is Kelvin, K (e.g. candlelight is 1500k, daylight at noon is 5500k).

CONTROLLED INTERSECTION

Intersection with a traffic light or other traffic control device.

CORRIDOR

Transportation pathway allowing movement between activity centers; a corridor may encompass single or multiple transportation routes and facilities, adjacent land uses, and the connecting street network.

COUNTDOWN CLOCK

Traffic signal feature notifying pedestrians of the time remaining to safely cross the intersection.

CRI

Color Rendering Index - A system used to describe the effect of a light source on the color/appearance of an object, compared to a reference source.  The index uses a scale from 0-100 and is used as a quality distinction.

CROSSWALK

Marked portion of the street designated for pedestrian crossing, either mid-block or at an intersection.  The most common markings are double parallel lines, ladder, and zebra stripes.

CURB EXTENSION

An extension of the sidewalk or curb line into the parking lane to reduce the effective street width. Also known as curb bulb-outs or neckdowns, curb extensions significantly improve pedestrian crossings by reducing the pedestrian crossing distance, visually and physically narrowing the roadway, improving the ability of pedestrians and motorists to see each other, and reducing the time that pedestrians are in the street.  Curb extensions are only appropriate where there is an on-street parking lane. Curb extensions should not extend more than 6 feet from the curb, and must not extend into travel lanes, bicycle lanes or shoulders. The turning needs of larger vehicles, such as school buses, need to be considered in curb extension design.

DAYLIGHTING

Strategies for increasing the percentage of illumination provided by natural light in a building, such as light shelves, toplighting, skylights, window, optimized building orientation and room layout, and devices used to redirect or transport light.

DENSITY

The number of dwelling units, buildings, or persons per unit of land, usually per acre (expressed as du/ac).

DESIGN VEHICLE

Vehicle that must regularly be accommodated on a roadway without encroachment into other travel lanes (e.g. an intersection on a transit route might be designed to accommodate the wide turning radius of the bus).

DETACHED SIDEWALK

A sidewalk separated from the curb by trees, grass, landscaping, lights, or other streetscape elements.

DIFFUSER

A device used to redirect of scatter light from a source.

EASEMENT

Contractual agreement allowing temporary or permanent access through and/or use of a property.

ENCLOSURE

Recognized as a key component of creating a satisfactory, comfortable space; spaces can be framed by landforms, fences, walls, structures, and trees/landscaping.

EXPRESSWAY

A divided highway, typically with a 150-200 foot right-of-way, with full or partial access control and interchanges at selected public roads.  Expressways may also have at-grade intersections spaced at 1500-2000 foot intervals.

FAR

Floor Area Ratio - The ratio of a building’s floor area to the area of the lot on which it is situated (Total building floor area / Total lot area); FAR is often used to determine the intensity of land use for zoning purposes.

FLUORESCENT

A low-pressure mercury electric discharge lamp.

FOOTCANDLE

A measure of the amount of visible light illuminating a surface from above;
1 fc = 10.764 lx, or lumens per square meter.

FREEWAY

A divided highway for through traffic with full access control and interchanges at selected public roads.

FUNCTIONAL CLASSIFICATION

A system for classifying streets and highways based on the nature of service they are intended to provide.

GLARE

A form of visual noise; an uncomfortably bright light source or reflection interfering with visual perception; glare can be described as direct, reflected, discomfort, disability, or blinding.

GREENWAY

A protected open-space area following a natural or man-made linear feature; greenways are often used for recreation, transportation, and conservation, and to link amenities.

HEADWAY

Scheduled time interval between two vehicles operating in the same direction on a transit route; may vary over the course of a day or week, with changes in rider demand.

HIGH INTENSITY DISCHARGE LAMP

An arc passing between two electrodes in a pressurized tube causes metallic additives to vaporize and produce light; HID lamps have a longer life and provide more lumens (light) per watt than many other light sources; available in mercury vapor, metal halide, and high/low pressure sodium.

HOV

High Occupancy Vehicle - A passenger vehicle carrying two or more persons; HOV lanes typically require a minimum number of occupants or charge a fee for a vehicle to use facilities.

HUMAN SCALE

Describes an area designed to allow pedestrians to comfortably walk from one location to another and interact with the built environment; an effort to create an appropriate relationship between human beings and the size/function of surrounding buildings; an emphasis on building features and characteristics which can be observed in close proximity, at the speed a pedestrian would travel.

HYDROLOGIC CYCLE

The cyclical movement of water between the earth and the atmosphere through precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transpiration.

IESNA

Illuminating Engineering Society of North American (IESNA) is the technical authority on illumination; the society seeks to promote good lighting practice, advance knowledge, and disseminate information through various publications.

IMPERVIOUS SURFACE

A hard surface which slows or prevents water from infiltrating the soil and/or causes water to run off the surface more rapidly or in greater quantities than under natural conditions, before development occurred.

INCANDESCENT LAMP

An element is headed to the point of incandescence by the passage of an electric current to produce light.

INFRASTRUCTURE

The built facilities required to serve a community’s development and operational needs, e.g. roads, water, and sewer systems.

INTERSECTION

The area where two or more roadways join or cross including the roadway and roadside facilities.

ITE

Institute of Transportation Engineers - An international association of transportation professionals that supports transportation-related education, research, professional development, public awareness programs, and facilitates the exchange of professional information.

LAND USE

The way in which a parcel of land is used or occupied, i.e. the types of buildings or activities, and/or the purpose for which it is designed, arranged, intended, or maintained.

LED

Light Emitting Diode - An electronic device that lights up when energy passes through it; LED’s can be blue, green, red, or white, are very energy-efficient, and have a long life.

LIGHT POLLUTION

Light directed to areas where it is not needed; light pollution directed into the sky makes it difficult to see stars at night.

LIGHT SHELF

A horizontal shelf positioned above eye level designed to reflect daylight onto the ceiling for daylighting purposes.

LOCAL STREET

Primary role is providing access to adjacent properties; local streets have low levels of mobility, and serve residential, commercial, and industrial areas.

LOS

Level of Service - A qualitative rating system used to describe the adequacy of the road network at a specific intersection or street segment, based on factors including travel time, freedom to maneuver, driver comfort, and interruptions; LOS A is used to describe the best traffic conditions while LOS F denotes gridlock.  LOS can also be used to describe transit and bicycle/pedestrian networks.

LPI

Leading Pedestrian Interval - An early WALK signal allowing pedestrians to begin crossing at an intersection before turning vehicles are released.

LUMINAIRE

A complete lighting unit or fixture.

MAJOR THOROUGHFARE

Major, multimodal streets in urban areas (arterials and collectors) which are designed to complement and support adjacent land uses.

MEDIAN

A raised barrier used to separate opposing traffic flow and control access and turning movements.  A median can also provide a pedestrian crossing refuge and streetscape enhancement.

MIXED-USE ZONING

Zoning allowing several types of uses (e.g. residential, commercial, office, and/or retail) within a single building or development.  The uses can be mixed vertically, with different uses stacked in a single building, or horizontally, with different uses adjacent to or near each other.

MOBILITY

Movement of people or goods within the transportation system.

MPO

Metropolitan Planning Organization - A federally required planning entity responsible for transportation planning and project selection in its region; every urbanized area with a population over 50,000 should have an MPO, designated by the governor.

MULTI-USE PATH

A bikeway physically separated from motorized vehicular traffic by an open space or barrier located either within the highway right-of-way or within an independent right-of-way.  Shared use paths may also be used by pedestrians, skaters, wheelchair users, runners, and other non-motorized users.

MULTIMODAL

A system or corridor providing a range of transportation options including walking, bicycling, driving, and transit.

MUTCD

Manual on Uniform Traffic Control Devices - The MUTCD defines the standards used for the installation and maintenance of traffic control devices (signs, signals, and pavement markings) nationwide; the manual is published by the Federal Highway Administration.

ON-STREET PARKING

Space for parking cars within the street right-of-way; on-street parking can improve access to nearby land uses, create a buffer between pedestrians and vehicles, and help reduce traffic speeds by narrowing the perceived right-of-way.

PEDESTRIAN CROSSING INTERVAL

The phases of a traffic signal cycle provided for a pedestrian to cross a roadway in a crosswalk, including the “walk” and “clearance” intervals.

PEDESTRIAN FRIENDLY

A built environment that emphasizes and is conducive to walking between destinations.  A pedestrian-friendly environment may include sidewalks, buffers, street trees, benches, fountains, transit stops, pedestrian-oriented signs and lighting, public art, and buildings that are visually interesting with high levels of transparency and articulation.

PEDESTRIAN RAMP

A sloped area of concrete connecting the street and the sidewalk to assist pedestrians crossing an intersection.

PEDESTRIAN REFUGE

A protected area between traffic lanes providing pedestrians with a safe place to wait for gaps in traffic.

PEDESTRIAN SCALE

Describes an area designed to allow pedestrians to comfortably walk from one location to another and interact with the built environment; an effort to create an appropriate relationship between human beings and the size/function of surrounding buildings; an emphasis on building features and characteristics which can be observed in close proximity, at the speed a pedestrian would travel.

PEDESTRIAN-ORIENTED

A built environment that emphasizes and is conducive to walking between destinations.  A pedestrian-friendly environment may include sidewalks, buffers, street trees, benches, fountains, transit stops, pedestrian-oriented signs and lighting, public art, and buildings that are visually interesting with high levels of transparency and articulation.

PHOTOVOLTAIC PANELS

Silicon panels collect sunlight and convert it into solar energy, which is then stored in special batteries, sent to a power inverter, and converted into a usable form; photovoltaic panels are joined together to create a solar array.

PLANTING STRIP

The area between the street right-of-way line and the sidewalk, intended to provide a buffer between pedestrians and vehicles.

REFUGE ISLAND

A protected area between traffic lanes providing pedestrians with a safe place to wait for gaps in traffic.

RIGHT-IN, RIGHT-OUT

A driveway or median where left turns are prohibited by physical or regulatory means.

ROAD DIET

Narrowing a roadway by reducing the number of lanes or lane width; a traffic calming strategy used to reduce vehicle speeds.  Road diets are often conversions of four-lane undivided roads into three lanes (two through lanes and a center two-way left turn lane (TWLTL). The ROW of the fourth lane may be used for bicycle lanes, sidewalks, and/or on-street parking.

ROADWAY

A thoroughfare at least twenty feet in width that has been dedicated to the public for transportation use; a section of the right-of-way that has been designed, improved, surfaced, or is typically used for motor vehicle travel.

ROUNDABOUT

A traffic calming device in which vehicles follow a circular path around a central island; upon approaching the roundabout, vehicles are expected to yield to traffic already in the circle.

ROW

Right-of-Way - Public strip of land on which streets, sidewalks, alleys, transit and railroad lines, and public utilities are built.

RUNOFF

Rainfall and other precipitation that flows into drainage facilities, bodies of water, and wetlands, or seeps through the soil to become shallow groundwater.

SAFE ROUTES TO SCHOOL

Programs designed to encourage and enable children to safely walk and bike to school. These programs often include education, encouragement and enforcement efforts in conjunction with a variety of site-specific engineering measures designed to improve safety for bicycling and walking.  See www.saferoutesinfo.org and http://safety.fhwa.dot.gov/saferoutes/ for more information.

SETBACK

The distance between a building and the property line or other buildings.

SHARED LANE

A wide outside/curb or shared lane (WCL) is the lane nearest the curb and is wider than a standard (12-foot) lane, providing additional space so that the lane may be shared more comfortably by motor vehicles and bicycles.  These lanes should be about 14 feet wide, as lanes wider than 15 feet can encourage the operation of two motor vehicles side by side.  If lanes become too wide, some motorists may also assume parallel parking is allowed, constricting the travel lane for bikes.

SHARED ROADWAY

A roadway that is open to both bicycle and motor vehicle travel - may be an existing roadway, street with wide curb/outside lanes, or road with paved shoulders. Shared roadways typically have no bikeway designation, but should be designed and constructed under the assumption that they will be used by bicyclists.  Lanes are typically 12 feet wide or less, allowing cars to safely pass bicyclists only by crossing the center line or moving into another traffic lane.

SHOULDER

The portion of the roadway to the right of the rightmost travel lane, excluding curbs, buffers, and sidewalks; shoulders can be paved, gravel, dirt, or grass, and serve a number of different purposes, (bicycle and pedestrian travel, structural roadway support, space for emergency vehicles to pass, stopped/disabled vehicle pull-off, space for vehicles to slow and turn right) typically dictated by their width and composition.

SIDEPATH

A type of multi-use path running adjacent and parallel to a roadway, like an extra wide sidewalk.  Sidepaths have special design challenges, as motor vehicles may not expect bikes to be entering an intersection from outside the travel lanes.  AASHTO discourages two-way paths located immediately adjacent to roadways due to the operational and safety issues that can occur.  Sidepaths should not be considered a substitute for street improvements even when the path is located adjacent to a highway, as many bicyclists find these paths less convenient than on-street facilities, particularly for utilitarian trips.

SIGHT DISTANCE

The distance a driver is able to see ahead; adequate sight distance is important to give drivers time to perceive and react to hazards or prepare to make decisions and maneuvers.

SIGNED SHARED ROADWAY

A shared roadway that has been designated with signing as a preferred route for bicycle use to provide continuity to other bicycle facilities, or to designate preferred routes through high-demand corridors.

STORMWATER

Water that runs off impervious surfaces (e.g. rooftops, pavement) during or after precipitation, car washing, over-watering laws, etc.

STREET FURNITURE

Fixtures installed along the roadway, at or above grade level, including lamp posts, pedestrian lighting, fire hydrants, street signs, benches, trash cans, bike racks, newspaper boxes, water fountains, and planters.

STREETSCAPE

The elements within and along the street right-of-way that define its appearance, identity, and functionality, including adjacent buildings and land uses, street furniture, landscaping, trees, sidewalks, and pavement treatments, among others.

SUBSTANTIVE SAFETY

Using the actual crash performance of geometric design choices, instead of relying solely on design standards, to evaluate safety.

TIP

Transportation Improvement Program - A short-term, three-year program of transportation projects which are expected to be federally funded; these projects are drawn from and should be consistent with the long-range transportation plan.

TOD

Transit Oriented Development - Development in which land uses are designed and sited to maximize transit ridership and the use of alternative forms of transportation; TOD’s are typically also mixed-use developments.

TRAFFIC CALMING

Transportation techniques, facilities, or programs designed to slow the movement of motor vehicles.  Traffic calming typically involves changes in street alignment, installation of barriers and other physical measures to reduce traffic speeds and/or cut-through volumes in the interest of safety, livability, and other public interests.  Physical treatments may include speed tables, raised crosswalks, textured pavement, roundabouts, chicanes, curb extensions, partial roadway closures, diagonal diverters and median barriers.

TRANSPARENCY

Requirement that a certain percentage of the façade between 2’ and 8’ above the adjacent walkway include clear or lightly tinted glass; transparency helps to create a more comfortable and inviting pedestrian environment.

TRAVELED WAY

The public right-of-way between curbs, including parking lanes, travel lanes (including bus and bicycle), medians, transit stops, curb and gutter, and loading/unloading zones.

VMT

Vehicle Miles Traveled - The number of vehicle miles traveled within a specified geographic area during a given period of time; one vehicle traveling one mile constitutes one vehicle mile, regardless of its size or the number of passengers.

WARRANT

The standardized conditions under which a traffic management technique is justified.

WATER TABLE

The upper level of the saturated/groundwater zone; the area where all open spaces are filled with water, just above groundwater.  The water table often functions as a transition zone, with a configuration similar to that of the overlying terrain.

WIDE OUTSIDE LANE

A wide outside/curb or shared lane (WCL) is the lane nearest the curb and is wider than a standard (12-foot) lane, providing additional space so that the lane may be shared more comfortably by motor vehicles and bicycles.  These lanes should be about 14 feet wide, as lanes wider than 15 feet can encourage the operation of two motor vehicles side by side.  If lanes become too wide, some motorists may also assume parallel parking is allowed, constricting the travel lane for bikes.

ZONING

Classification system based on permitted and prohibited land uses, densities, and intensities used to promote land use compatibility.

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