Glossary

Air control facility: A station that provides air traffic control service to aircraft operating on an IFR (instrument flight rule) flight plan within controlled airspace and principally during the en route phase of flight.

Aircraft sequencing: Automation technology that helps air traffic controllers maximize runway space by managing aircraft arrival and departure rates.

Airlift: Both the means of delivery and the sustainable lifeline for troops by air until sea lines of communication can be established.

Alternative fuels: Methanol, denatured ethanol, and other alcohols, separately or in mixtures of 85 percent by volume or more (or other percentage not less than 70 as determined by Department of Energy rule) with gasoline or other fuels. Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), Liquefied Petroleum Gas (LPG), hydrogen, coal-derived liquid fuels, fuels other than alcohols derived from biological materials, electricity, or any other fuel determined to be substantially not petroleum.

Anthropogenic interference: Of, relating to, or resulting from the influence of human beings on nature.

Arterial (highway): A major highway, primarily for through traffic, usually on a continuous route.

Avionics: Aviation communications, navigation, flight controls, and displays.

A-weighted scale: Scale that measures those sound frequencies humans can most easily hear. Measurements of decibels are nonlinear; a 10-decibel increase in sound on a scale of A-weighted decibels (dBA) represents a perceived doubling of sound. A vacuum cleaner operating 10 feet away is audible at 70 to 75 dBA. Noise becomes annoying at 65dBA and painful at 128 dBA.

Ballast (rail): Cinders, crushed rock, or gravel placed on the roadbed to hold track ties in place and to promote uniform drainage.

Ballast (sea): Heavy substances loaded by a vessel to improve stability. Seawater ballast is commonly loaded in most vessels in ballast tanks.

Barge carriers: Ships designed to carry either barges or containers exclusively, or some variable number of barges and containers simultaneously. Currently, this class includes two types of vessels, the LASH and the SEABEE.

Barge: A nonmotorized water vessel, usually flat-bottomed and towed or pushed by a tugboat or pushboat.

Beam: The width of a ship. Also called breadth.

Berth: A place in which a vessel is moored or secured.

Bilateral Agreement: A concurrence reached between two states.

Bilge keel: One of a pair of longitudinal plates that, like fins, project from the sides of a ship or boat and run parallel to the center keel. They are intended to check rolling. On large ships the outward projections of the bilge keels may be slight; on small yachts they may be comparatively deep.

Bill of lading: A document by which the master of a ship acknowledges having received in good order and condition (or the reverse) certain specified goods. A bill of landing specifies the name of the master, the port and destination of the ship, the goods, the consignee, and the rate of the freight.

Biometric identification systems: Identification systems involving voice recognition, handprint, and face scans.

Blind spot: Areas around a commercial vehicle that are not visible to the driver either through the windshield, side windows, or mirrors.

Break bulk: The process of assimilating many small shipments into one large shipment at a central point so that economies of scale may be achieved; to commence discharge of cargo.

Breakbulk vessel: A cargo ship that carries a variety of products of nonuniform sizes, often bound on pallets to facilitate loading and unloading.

Brownfield sites: Abandoned, idled, or underused industrial and commercial facilities/sites where expansion or redevelopment is complicated by real or perceived environmental contamination. They can be in urban, suburban, or rural areas. The Environmental Protection Agencys Brownfields initiative helps communities mitigate potential health risks and restore the economic viability of such areas or properties.

Bulk Carrier: Vessels designed to carry dry-bulk cargo such as grain, fertilizers, and ore.

Cabotage: The carriage of goods or passengers for remuneration taken on at one point and discharged at another point within the territory of the country.

Car capacity: Load limitation, by volume or weight, of a rail freight car.

Carload: A shipment of not less than 10,000 pounds of one commodity from one consignor to another.

Circumferential commuting pattern: Commuting between suburban areas on the fringe of a city.

Civil Reserve Air Fleet: Provides a significant part of the nations mobility resource. Selected aircraft from commercial U.S. airlines are contracted to support Department of Defense emergency airlift requirements should airlift needs exceed military aircraft capabilities.

Class I railroads: A railroad with an annual gross operating revenue in excess of $250 million (1991 dollars).

Collector (highway): In rural areas, highway routes serving intra-county rather than statewide travel. In urban areas, roads providing direct access to neighborhoods as well as to arterials.

Commuter air carrier: A small certificated air taxi operator performing at least five round trips per week between two or more points according to published flight schedules that specify times, days of the week, and points between such flights.

Commuter rail (transit): Urban passenger train service for short-distance travel between a central city and adjacent suburb. Does not include rapid-rail transit or light-rail service.

Compact car: An automobile industry designation applied to cars with a wheelbase between 100 and 104 inches.

Container: A rectangular box used to transport freight by ship, rail, and highway. International shipping containers are 20 or 40 feet long, conform to International Standards Organization standards, and are designed to fit in ships holds. Off the ship, containers are transported on public roads on a container chassis towed by a tractor. Domestic containers, up to 53 feet long and of lighter construction, are designed for rail and highway use only.

Corporate Average Fuel Economy (CAFE): Originally established by Congress for new automobiles, and later for light trucks. CAFE standards require automobile manufacturers to produce vehicle fleets with a composite sales-weighted fuel economy that meets or exceeds the CAFE standards in a given year. For every vehicle that does not meet the standard, a fine is paid for every one-tenth of a mpg below the standard.

Culvert: A sewer or drain running under a road, railroad tracks, or an embankment.

Daymarker: An unlighted shore aid to navigation, either diamond, square, or triangle shaped.

DC traction motor: The motive power of the train is provided by a motor powered by direct current through overhead electrified wires.

Deadweight: The number of tons (metric or long) of cargo, stores, and bunker fuel that a vessel can transport. It is the difference between the number of tons of water a vessel displaces light and the number of tons it displaces when submerged to the load line.

Dependence ratio: The ratio of household members who are not of working age (either under 16 or over 65) to those of working age. This results in more persons living in households in which they are responsible for supporting only themselves as opposed to supporting dependents (i.e., children or aging parents).

Doppler effect: The apparent difference between the frequency at which sound or light waves leave a source and that at which they reach an observer, caused by relative motion of the observer and the wave source.

Doublestack rail services: Intermodal service characterized by shipping containers stacked two-high on railcars.

Dredge: The act of cleaning, deepening, or widening harbors and waterways with a machine equipped with a scooping or suction device. This equipment is also called a dredge.

Dry bulk: Cargo such as grain, fertilizers, and ore.

Dry-cargo ships: Large flat-bottomed, nonself-propelled vessels used to transport dry bulk materials such as coal and ore.

Dynamic routing: In demand-response transportation systems, the process of constantly modifying vehicle routes to accommodate service requests received after vehicles begin operations, as distinguished from predetermined routes assigned to a vehicle.

Enplanement: The total number of passengers boarding an aircraft and the total revenue tons of freight and mail loaded on an aircraft.

Environmental impact statement: A document required of federal agencies by the National Environmental Policy Act for major projects or legislative proposals significantly affecting the environment. The statement describes the positive and negative effects of the undertaking and cites alternative actions.

Environmental streamlining: The development and implementation of an environmental review process for highway and transit projects that coordinates the regulations of all agencies affected by the project. One element of the streamlining process is concurrent review, another is a review slated for completion within a cooperatively determined time period.

Ex-urban: Rural location on the fringes of a suburban area having residents who commute to work in urban areas.

Final approach spacing tools: The use of aircraft descent performance characteristics, position/track data, user preferences, and controller inputs to generate a recommended arrival/landing sequence for each plane.

Fixed-wing turbine aircraft: An aircraft with an internal-combustion engine to turn a turbine.

Flag of convenience: Sometimes referred to as flag of necessity; denotes registration of a ship to a nation, other than the nation of the vessels owner, that offers favorable tax structures, regulations, and other incentives.

Force deployment: The moving of military units outside the borders of a state.

Foreign flag air carrier: A foreign air carrier that makes stops within the borders of the United States.

Free flight phase 1: To be introduced by 2002, will use advanced airborne and ground-based technologies and new procedures to gain optimum tactical separation between planes, enabling more planes to fly and to take more efficient, more direct routes.

Free flight: a system using advanced technologies and procedures that give air crews more freedom to select flight paths, speeds, and altitudes that are the most direct or otherwise satisfy operational requirements.

Fuel cell: A device that produces electrical energy directly from the controlled electrochemical oxidation of the fuel. It does not contain an intermediate heat cycle, as do most other electrical generation techniques.

Gauge (rail): The distance measured between the inside edges of the running rails.

GDP (gross domestic product): Total market value of goods and services produced by a nations economy during a specific period of time (usually a year), plus the income accruing to a nations residents from investments abroad, minus the income earned in the domestic economy accruing to non-nationals located abroad (see GNP (gross national product)).

Geostationary orbit: Any orbit at an altitude of 23,000 miles above the equator traveling at a velocity and in a direction that keeps pace with the Earths rotation, making it appear to be stationery in the sky (see Geosynchronous).

Geosynchronous orbit: Any orbit that has a rotational period equal to that of the Earths rotational period and which may or may not be positioned over the equator. Geosynchronous orbits inclined to the equator pass over the same points of the Earth at the same time each day. Geosynchronous orbits over the equator appear to be stationary (see Geostationary).

GNP (gross national product): Total market value of the final goods and services produced by a nations economy during a specific period of time (usually a year), computed before allowance is made for the depreciation or consumption of capital used in the process of production (see GDP).

GWP (gross world product): Aggregate value of all final goods and services produced worldwide in a given year.

Hazardous material (Hazmat): A substance or material that has been determined to be capable of posing an unreasonable risk to health, safety, and property when transported in commerce.

Heavy rail (transit): An electric railway with the capacity for a heavy volume of traffic and characterized by exclusive rights-of-way, multicar trains, high speed and rapid acceleration, sophisticated signaling, and high platform loading. Also known as subway, elevated (railway), or metropolitan railway (metro).

High-occupancy vehicle lanes: Exclusive road or traffic lane limited to buses, vanpools, carpools, and emergency vehicles.

High-occupancy vehicle: A vehicle that can carry at least two passengers, for example, a car, bus, or van.

Highway Trust Fund (HTF): The source of funding for programs described in a particular Act. The HTF under the Transportation Equity Act for the 21st Century is composed of the Highway Account, which funds highway and intermodal programs, and the Mass Transit Account. Federal motor fuel taxes are the major source of income into the HTF.

Highway-rail grade crossings: A location where one or more railroad tracks cross a public highway, road, or street or a private roadway at grade, including sidewalks and pathways at, or associated with, the crossing.

Household-trip: One or more household members traveling together.

Hub: A central location to which traffic from many cities is directed and from which traffic is fed to other areas

Hull loss: Serious damage or destruction to an aircraft due to an accident.

Hybrid vehicle: A vehicle powered by both an internal combustion engine and an electric motor. The emission levels of hybrid vehicles are lower than vehicles powered solely by an internal combustion engine.

Hydrographic survey: Surveying of underwater features.

Intercity rail system: Transportation provided by Amtrak.

Intermodal: Pertaining to transportation using a combination of two or more land, sea, or air systems.

Joint Aviation Authorities: An associated body of the European Civil Aviation Conference representing the civil aviation regulatory authorities of a number of European states who have agreed to cooperate in developing and implementing common safety regulatory standards and procedures. This cooperation is intended to provide high and consistent standards of safety and a level playing field for competition in Europe. Much emphasis is also placed on harmonizing JAA regulations with those of the United States. The JAA Membership is based on signing the JAA Arrangements document originally signed by the then current member States in Cyprus in 1990.

Just-in-time: The principle of production and inventory control in which goods arrive when needed for production or use.

Lean-burn gasoline: Lean combustion engines were designed to enhance fuel efficiency without sacrificing power or drivability. All engines burn a mixture of air and fuel, but a lean-burn engine has a higher air-to-fuel ratio than conventional engines. This can mean significant savings in petrol, and thus in emissions like CO2.

Lighter aboard ship: An ocean ship that carries barges. These barges are loaded with cargo, often at a variety of locations, towed to the ocean ship, sometimes referred to as the mother ship, and lifted or, in some cases, floated on board. After the ocean crossing, the barges are off-loaded and towed to their various destinations. This type of ship eliminates the need for specialized port equipment.

Lightships: Navigation aids consisting of unmanned small vessels equipped with lights. Phased out in the early 1980s.

Line haul: The management of freight transported between cities, usually more than 1,000 miles apart.

Liner: A cargo-carrying ship that is operated between specified ports on a regular basis for an advertised price, versus a chartered ship that operates for single deliveries to a variety of ports.

Liner trade: The passage of ships between designated ports on a fixed schedule and at published rates.

Livable Communities Initiative: Aimed at broadening choices available to communities and empowering them to sustain prosperity and expand economic opportunity by strengthening local and regional economies, reclaiming brownfields, achieving a more favorable jobs to housing balance, and encouraging smart growth.

Loop detector: An inductive loop of insulated wire, usually embedded in a roadbed, that detects metal objects that cross its path. Used to control such devices as traffic lights, toll collection systems, and motorized gates and doors.

Load factor: Percentage of cargo or passengers carried in relation to total capacity, for example, 4,000 tons carried on a vessel of 10,000 ton capacity has a load factor of 40 percent.

Loran: An electronic navigational system by which hyperbolic lines of position are determined by measuring the difference in the time of reception of synchronized pulse signals from two fixed transmitters. Loran A operates in the 1,750-1,950 kHz frequency band. Loran C and D operate in the 100-110 kHz frequency band.

Maintenance-of-way equipment (rail): Machinery and rolling stock used to keep track and roadbed in good operating condition.

Manifest: A listing or invoice-of-charge for a particular shipment of goods and material.

Micro-bursts (air): A small downburst with outbursts of damaging winds extending 2.5 miles or less. In spite of its small horizontal scale, an intense microburst could induce wind speeds as high as 150 knots.

Multilateral agreement: Agreement reached between more than two states and to which all signatories are bound, example the World Trade Organization. Compare with Plurilateral.

Multimodal: See intermodal.

Narrowbody aircraft: A commercial passenger jet having a single aisle and maximum of three seats on each side of the aisle. Narrowbody aircraft include B727, B737, B757, DC9, MD80, MD90, and A320.

Oil sands: Deposit of loose sand or partially consolidated sandstone that is saturated with highly viscous bitumen. Oil recovered from tar sands is commonly referred to as synthetic crude and is a potentially significant form of fossil fuel.

Oil shale: Any sedimentary rock containing solid organic material that yields hydrocarbons, along with a variety of solid products, when subjected to pyrolysisa treatment that consists of heating the rock to about 500C.

Omega system: An area navigation (RNAV) system designed for long-range navigation based on ground-based electronic navigational aid signals.

On-demand air taxi: Use of an aircraft operating under Federal Aviation Regulations, Part 135, passenger and cargo operations, including charter and excluding commuter air carrier.

Over-the-road bus: A bus characterized by an elevated passenger deck located over a baggage compartment, more commonly known as an intercity bus or motorcoach.

Paratransit: Comparable transportation service required by the American Disabilities Act for individuals with disabilities who are unable to use fixed-route transportation systems.

Park-and-ride: An access mode to transit in which patrons drive private automobiles or ride bicycles to a transit station, stop, or carpool/vanpool waiting area and park the vehicle in the area provided for the purpose. They then ride the transit system or take a car or vanpool to their destination.

Particulates: Carbon particles formed by partial oxidation and reduction of the hydrocarbon fuel. In the transportation sector, particulates are emitted mainly from diesel engines.

Pavement loops: Electronic devices installed beneath the surface of a road that can detect the passing of a car. Based on the frequency of passing cars, traffic flow can be monitored and controlled using computer-based traffic control systems. See loop detector.

Pedalcyclists: A person on a vehicle powered solely by pedals.

Person trip: Trip by one person using any mode of transportation. For example, four people traveling together in one auto equal four person trips.

Plurilateral agreement: Treaty between more than two states reached within the auspices of a multilateral agreement. However, not all multilateral signatories are bound to the plurilateral agreement unless they have specifically committed themselves to it.

Positive train controls (PTC): The application of digital data communications, automatic positioning systems, wayside interface units (to communicate with switches and wayside detectors), on-board and control center computers, and other advanced display, sensor, and control technologies to manage and control railroad operations. PTC can help reduce the probability of collisions between trains, collisions between trains and maintenance-of-way crews, and overspeed accidents. PTC systems can also improve the efficiency of railroad operations by reducing some train over-the-road delays, increasing running time reliability, increasing track capacity, and improving asset utilization.

Power Projection Platforms (PPP): U.S. military bases from which armed forces are moved to seaports for military deployment.

Radial commuting pattern: Commuting from suburban areas on the fringes of a city towards its center or core.

Ramjet: An air-breathing jet engine that operates with no major moving parts. It relies on the crafts forward motion to draw in air and on a specially shaped intake passage to compress the air for combustion. Ramjets work best at speeds of Mach 2 (twice the speed of sound) and higher.

Ramp metering programs: Control devices on entrance ramps that regulate the amount of traffic entering a freeway.

Regenerative brakes: A system wherein much of the braking and deceleration energy is recouped and returned to the battery to increase overall efficiency rather than being wasted as heat.

Revenue passenger miles: One passenger carried one mile generates one passenger-mile.

Revenue ton-miles: One ton of revenue cargo (including all baggage) transported one mile. Right of establishment: The right of airlines to create or purchase subsidiary airlines within a foreign nation.

Right-of-way: 1. The track, roadbed, and property alongside which is owned by the railroad. 2. The land acquired for and devoted to highway transportation.

Roll on/roll off vessel (water): Ships that are especially designed to carry wheeled containers or other wheeled cargo, and use the roll on/roll off method for loading and unloading.

Route sequencing (air): Process by which an air-traffic controller issues instructions to pilots on the proper flight headings, altitudes, and speeds to maintain separation from other aircraft and ensure safe and efficient order of arrivals, departures, and en route traffic.

Sealift: U.S.-controlled maritime or aviation shipping capacity used in times of military emergencies.

Seat-miles: The aircraft-miles flown between airports multiplied by the number of seats available on that flight for revenue passenger use. Seventy-five passengers flying 300 miles would equal 22,500 seat miles.

Smart growth: A concept intended to promote the quality of life in existing urban areas, limit urban sprawl, and promote a sense of community. Policies stemming from smart growth include the restoration of center cities and older suburbs, investment in transit and pedestrian forms of transportation, a greater mix of housing, commercial, and retail uses and the preservation of open space and many other environmental amenities.

Smart pigs: Devices that travel inside a pipe and are able to detect corrosion, metal loss, and mechanical gouges or dents.

Stages 2 and 3 aircraft: Under Federal Aviation Regulation Part 36, aircraft sound levels are categorized by stages. Stage 2 is the aircraft sound level needed to meet FAA 1969 noise regulations. Examples of Stage 2 aircraft include the B-727-200 and the DC 9. Stage 2 regulations are being phased out. Stage 3 refers to aircraft sound levels needed to meet FAAs more stringent 1975 noise regulations. Examples include the B-737-300, the B-757, the MD-80, and the A-310. Stage 3 aircraft noise levels range from 95 to 105 dBA.

Station cars: Electric vehicles driven to and from mass transit stations by transit riders. Typically, they are battery-powered, two-seat vehicles designed to transport transit users who cannot reach their final destinations by walking. They are intended to provide an option that could encourage transit use by those who otherwise would be compelled to drive their own vehicles.

Steel wheel (rail): The cast or forged steel wheel that rolls on the rail, carries the weight, and provides guidance for rail vehicles. The wheels are semipermanently mounted in pairs on steel axles and are designed with flanges and a tapered treat to provide for operation on track of a specific gauge. The wheel also serves as a brake drum on cars with on-tread brakes.

Supersonic combustion ramjet (scramjet): An air-breathing engine designed for speeds beyond Mach 6, which mixes fuel into air flowing through it at supersonic speeds, used in hypersonic aircraft.

Supply chain: A set of three or more organizations directly linked by one or more of the upstream and downstream flows of products, services, finances, and information from a source to a customer.

Supply chain management: The systematic, strategic coordination of traditional business functions within a particular company and across businesses within the supply chain for the purposes of improving the long-term performance of the individual companies and the supply chain as a whole.

Tanker: An oceangoing ship designed to haul liquid bulk cargo in world trade.

Tier II: Environmental Protection Agency (EPA) regulations that cover motor vehicles and the fuels they use. These standards require a reduction in tailpipe emissions and lower sulfur content. These regulations specify acceptable ranges for some fuel qualities (e.g., volatility, sulfur content). In areas of the country with severe ozone problems, EPA requires the use of gasoline that has been reformulated to meet a predicted level of emissions performance, based on a range of fuel characteristics.

Tractor: Truck designed primarily to pull a semitrailer by means of a fifth wheel mounted over the rear axels. Sometimes called a truck-tractor or highway tractor to differentiate it from a farm tractor.

Tractor-trailer: Tractor and semitrailer combination

Traffic calming techniques: Road design strategies to reduce vehicle speeds and volumes. Traffic calming projects can range from a few minor changes to neighborhood streets to major rebuilding of a street network. Impacts range from moderate speed reductions on residential streets to arterial design changes.

Traffic signal control system: A system that controls traffic flow by adjusting and coordinating traffic signals at intersections. The system can also monitor traffic conditions with vehicle detectors and cameras. These functions allow a traffic management agency to service traffic demand, share traffic status with other agencies and with the traveling public, and operate and maintain the traffic signal control system.

Trestle: A wooden bridge-like structure usually having all supporting members below the railway tracks.

Trip chaining: The incorporation of multiple stops in one trip, instead of several individual trips, thus reducing fuel consumption.

Trust funds: Accounts that are specifically designated by law to carry out specific purposes and programs. They are usually financed with earmarked tax collections.

Turbojet/turbofan: Jet engine in which a turbine-driven compressor draws in and compresses air, forcing it into a combustion chamber into which fuel is injected. Ignition causes the gases to expand and to rush first through the turbine and then through a nozzle at the rear. Forward thrust is generated as a reaction to the rearward momentum of the exhaust gases. During the 1960s, the turbofan, a modification of the turbojet, came into common use. The turbofan moves a much greater mass of air than the simple turbojet, providing advantages in power and economy.

Twenty-Foot Equivalent Unit (TEU): A measure of containers carrying capacity determined by calculating the length of that container divided by 20. A 48 ft container equals 2.4 TEU. Two-way end-of-train device: Provides an additional measure of safety to a trains braking system, particularly on steep grades, by enabling locomotive engineers to apply an emergency brake from both ends of the train.

U.S. flag carrier or American flag carrier (air): A class of air carriers holding a Certificate of Public Convenience and Necessity issued by the Department of Transportation, approved by the President, authorizing scheduled operations over specified routes between the United States (and/or its territories) and one or more foreign countries.

Unit train: A train with a specified number of railcars that remains as a unit for a designated destination or until a change in routing is made.

Unlinked passenger trips: The number of passengers who board public transportation vehicles. A passenger is counted each time he/she boards a vehicle even though he/she may be on the same journey from origin to destination.

Vehicle-miles of travel (VMT): A unit of measurement of vehicle travel made by a private vehicle, such as an automobile, van, pickup truck, or motorcycle. Each mile traveled is counted as one vehicle-mile regardless of the number of persons in the vehicle.

Vehicle occupancy: The number of persons, including driver and passenger(s) in a vehicle. Nationwide Personal Transportation Survey occupancy rates are generally calculated as person-miles divided by vehicle-miles.

Vessel feeder services: Cargo to/from regional ports are transferred to/from a central hub port for a long-haul ocean voyage.

Vessel sharing agreement: An agreement between ocean common carriers whereby a carrier or carriers agree(s) to provide vessel capacity for the use of another carrier or carriers in exchange for compensation or services.

Volatile organic compounds: Gases released into the air from certain solids or liquids such as gasoline, solvents, and paint thinner. They include a variety of chemicals that can have both short-term and long-term health effects as well as contribute to global warming.

Voluntary security consortia: Cooperative group established at 170 airports that brings together government agencies and airline industry representatives to assess and discuss security issues and work together to eliminate vulnerabilities.

Wake turbulence: Every aircraft in flight generates a wake of turbulent air. The disturbance created by the wake is caused by a pair of counter rotating vortices trailing from the wingtips of the aircraft. The vortices from large aircraft pose problems to encountering aircraft. and if encountered at close range, can damage aircraft components and equipment and cause deaths or injuries.

Watersheds: Area from which all precipitation flows to a single stream or set of streams.

Waybill: Freight car handling order identifying the shipper, receiver, routing, and contents of the car.

Weigh-in motion: The process of measuring the dynamic tire forces of a moving vehicle and estimating the corresponding tire loads of the static vehicle. Weigh-in-motion technology provides highway planners and designers with traffic volume and classification data by time of day and day of week.

Wet lease: An arrangement for renting an aircraft under which the owner provides, for example, crews, ground support equipment, and fuel.

Wetlands: Areas that are neither fully terrestrial nor fully aquatic. They range from the vast cypress swamps of the southern United States to shallow holes that retain water only a few weeks of the year. Wetlands can provide critical habitat for migratory waterfowl, control flooding, act as natural filters for drinking water, and provide recreation.

Widebody aircraft: A commercial passenger jet having a twin aisle, able to hold a greater number of passengers than narrowbody aircraft. Examples include Boeings 747, 777 and Airbuss A310.

Windshear: A sudden and dramatic shift in wind speed and direction.