Air carrier: Certificated provider of scheduled and nonscheduled services.

Chained dollars: A method to measure real changes in dollar values between years that uses chain-type indexes, rather than constant dollars. The method first calculates the real changes between adjacent years. Annual rates of real changes are then chained (multiplied) together to obtain the rate of real changes between nonadjacent years.

Class I railroad: Railroads earning adjusted annual operating revenues for three consecutive years of $250,000,000 or more, based on 1991 dollars with an adjustment factor applied to subsequent years.

Commercial waterway facilities: Waterway facilities, as defined by the U.S. Army Corps of Engineers, are piers, wharves, and docks. Not included are those facilities used exclusively for recreational or active military craft and generally those providing nonmaritime use.

Commuter rail: Urban/suburban passenger train service for short–distance travel between a central city and adjacent suburbs run on tracks of a traditional railroad system. Does not include heavy or light rail transit service.

Contracted service (purchased transportation): Transportation service provided to a public transit agency or governmental unit from a public or private transportation provider based on a written contract.

Current dollars: The market value reflecting prices and quantities of the period being measured.

Demand–response transit: A nonfixed–route, nonfixed–schedule form of transportation that operates in response to calls from passengers or their agents to the transit operator or dispatcher.

Directional route miles: The sum of the mileage in each direction over which transit vehicles travel while in revenue service.

Directly operated service: Transportation service provided directly by a transit agency, using their employees to supply the necessary labor to operate the revenue vehicles.

Draft: The depth of water a vessel draws, loaded or unloaded.

Enplaned passengers: Total number of revenue passengers boarding aircraft.

Ferry: Vessels that carry passengers and/or vehicles over a body of water. Generally steam or diesel-powered, ferryboats may also be hovercraft, hydrofoil, and other high-speed vessels. The vessel is limited in its use to the carriage of deck passengers or vehicles or both, operates on a short run on a frequent schedule between two points over the most direct water routes other than in ocean or coastwise service, and is offered as a public service of a type normally attributed to a bridge or tunnel.

For-hire: Refers to a vehicle operated on behalf of or by a company that provides transport services to external customers for a fee. It is distinguished from private transportation services, in which a firm transports its own freight and does not offer its transportation services to other shippers.

Functionally Obsolete: Functional obsolescence is a function of the geometrics of the bridge not meeting current design standards.

General aviation: Civil aviation operations other than those air carriers holding a Certificate of Public Convenience and Necessity. Types of aircraft used in general aviation range from corporate, multi–engine jets piloted by a professional crew to amateur–built, single–engine, piston–driven, acrobatic planes.

Gross Domestic Product: The total value of goods and services produced by labor and property located in the United States. As long as the labor and property are located in the United States, the suppliers may be either U.S. residents or residents of foreign countries.

Heavy rail transit: High-speed transit rail operated on rights–of–way that exclude all other vehicles and pedestrians.

Hybrid vehicle: Hybrid electric vehicles combine features of internal combustion engines and electric motors. Unlike 100% electric vehicles, hybrid vehicles do not need to be plugged into an external source of electricity to be recharged. Most hybrid vehicles operate on gasoline.

Large certificated air carrier: Carriers operating aircraft with a maximum passenger capacity of more than 60 seats or a maximum payload of more than 18,000 pounds. These carriers are also grouped by annual operating revenues: majors—more than $1 billion; nationals—between $100 million and $1 billion; large regionals—between $20 million and $99,999,999; and medium regionals—less than $20 million.

Light rail transit: Urban transit rail operated on a reserved right-of-way that may be crossed by roads used by motor vehicles and pedestrians.

Light duty vehicle long wheelbase: Large passenger cars, vans, pickup trucks, and sport/utility vehicles with wheelbases larger than 121 inches.

Light duty vehicle short wheelbase: Passenger cars, light trucks, vans and sport utility vehicles with a wheelbase equal to or less than 121 inches.

Light truck: Trucks of 10,000 pounds gross vehicle weight rating or less, including pickup trucks, vans, truck-based station wagons, and sport utility vehicles.

Long–distance travel: Long-distance trips are trips of 50 miles or more from home to the farthest destination traveled and include the return component as well as any overnight stops and stops to change transportation mode.

Metric ton: A unit of weight equal to 2,204.6 pounds.

North American Industry Classification System (NAICS): NAICS (established in April 1997) replaced the Standard Industrial Classification (SIC) and groups producing and nonproducing economic activities into 20 sectors and 1,170 industries in the United States version. It was developed to provide common industry definitions for Canada, Mexico, and the United States to facilitate analyses of the economies of the three countries.

Nonself–propelled vessels: Includes dry cargo, tank barges, and railroad car floats that operate in U.S. ports and waterways.

Particulates: Carbon particles formed by partial oxidation and reduction of hydrocarbon fuel. Also included are trace quantities of metal oxides and nitrides, originating from engine wear, component degradation, and inorganic fuel additives.

Passenger-mile: One passenger transported one mile. For example, one vehicle traveling 3 miles carrying 5 passengers generates 15 passenger–miles.

Pedalcyclist: A person on a vehicle that is powered solely by pedals.

Personal communication: Involves contacting the source for data if not publicly available.

Real gross domestic product (GDP): Real gross domestic product is the inflation adjusted value of the output of goods and services produced by labor and property located in the United States.

Self–propelled vessels: Includes dry cargo vessels, tankers, and offshore supply vessels, tugboats, pushboats, and passenger vessels, such as excursion/sightseeing boats, combination passenger and dry cargo vessels, and ferries.

Serious injury: An injury that requires hospitalization for more than 48 hours, commencing within 7 days from the date when the injury was received; results in a bone fracture (except simple fractures of fingers, toes, or nose); involves lacerations that cause severe hemorrhages, nerve, muscle, or tendon damage; involves injury to any internal organ; or involves second- or third-degree burns or any burns affecting more than 5 percent of the body surface.

Short ton: A unit of weight equal to 2,000 pounds.

Structurally Deficient: Structural deficiencies are characterized by deteriorated conditions of significant bridge elements and reduced load-carrying capacity.

Ton-mile: A unit of measure equal to movement of one ton over one mile.

Truck: Single unit—A large truck on a single frame with at least two axles and six tires. Combination—A power unit (truck or truck tractor) and one or more trailing units.

Vehicle-mile: One vehicle traveling one mile.