USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Terminology for the Transportation Services Index

Tuesday, March 5, 2024


Aggregate A total created from smaller units. For instance, the population of a county is an aggregate of the populations of the cities, rural areas, and so forth, that make up the county.

Aggregate data Data that have been combined from data for components. (See Disaggregate data.)

Air taxi Air carriers that transport persons, property, and mail using small aircraft (under 30 seats or a maximum payload capacity of 7,500 lb).

Air Transport Association A trade association for the air transport industry. It supports and assists its members by promoting the air transport industry, advocating common industry positions before state and local governments, and conducting designated industry-wide programs.

American Trucking Associations, Inc. (ATA) A major national federation of trucking industry associations. ATA's membership includes associations covering carriers in most trucking industry segments.

Association of American Railroads (AAR) A trade association that represents the major freight railroads of the United States, Canada, and Mexico. Amtrak and some regional commuter railroads are also members of the AAR. In addition, the AAR has associate members including smaller freight railroads, railway suppliers, and other companies with an interest in railroads.

Arima process AutoRegressive Integrated Moving Average

Autoregressive moving average model A statistical time series model that uses a regression relationship based on historical time series values to predict future time series values.

Average trip length (transit) The average distance ridden for an unlinked passenger trip, which is computed as passenger-miles traveled divided by the number of unlinked passenger trips.


Barrel (petroleum) 42 U.S. gallons of petroleum.

Bus (transit) A transit mode consisting of rubber-tired passenger vehicles operating on routes and schedules over roadways.

Business cycle A long-term pattern of periods of real economic growth alternating with periods of economic decline.


Carload (rail) A shipment of freight that fills a rail car.

Chaining In the context of indexing, calculating the index number of any period relative to the base period as the final product of the multiplication of the changes between consecutive periods from the base period to the period for which the index number is calculated. For example, the index number of 2003 from base year 2000 is calculated as the product of the consecutive multiplication of the change of 20002001, the change of 2001-2002, and the change of 20022003.

Coincident indicator Tends to move along with GDP; that is, when GDP increases, it increases, and vice versa. (See Lagging indicator and Leading indicator.)

Certificated air carrier Air carrier holding a Certificate of Public Convenience and Necessity issued by the U.S. Department of Transportation to conduct scheduled services interstate. These carriers may also conduct nonscheduled or charter operations.

Commercial air carrier An air carrier certificated in accordance with Federal Aviation Regulations (FAR) Part 121 or 127 to conduct scheduled services on specified routes. These air carriers may also provide nonscheduled or charter services as a secondary operation.

Commuter air carrier For economic regulations and reporting requirements, commuter air carriers are those carriers that operate aircraft of 60 or fewer seats or a maximum payload capacity of 18,000 pounds or less. These carriers hold a certificate issued under section 298C of the Federal Aviation Act of 1958, as amended.

Commuter rail (transit) A transit mode that is an electric- or diesel-propelled railway for urban passenger train service consisting of local, short-distance travel operating between a central city and adjacent suburbs.

Crude oil A mixture of hydrocarbons that exists in liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities. Crude oil is refined to produce a wide array of petroleum products, including heating oils; gasoline, diesel and jet fuels; lubricants; asphalt; ethane, propane, and butane.


Data dictionary A collection of data element definitions and may cover the whole organization, a part of the organization, or a database.

Deseasonalized data A series of data points over time that are adjusted, using statistical techniques, to remove increases or decreases due to time of year. Also referred to as seasonally adjusted data.

Deseasonalized time series A time series that has had the effect of seasonal variations removed by dividing each original time series observation by the corresponding seasonal index.

Disaggregate data Data that are separated into units, not combined. (See Aggregate data.)

Domestic commerce (maritime) Contiguous and noncontiguous states and territories constitute the geographical space on which domestic commerce may be transported. This includes Hawaii, Alaska, the 48 contiguous states, Puerto Rico and the Virgin Islands, Guam, American Samoa, Wake Island, and the U.S. Trust Territories.



Fisher ideal price index The geometric mean of the change in the average price with the quantities of the base period as the weights and the change in the average price with the quantities of the current period as the weights. (See Aggregation and Chaining in the TSI Methodology.)

Foreign commerce (maritime) Foreign commerce is waterborne imports, exports, and intransit traffic between the United States, Puerto Rico, and the Virgin Islands and any foreign country. These statistics do not include traffic between Guam, Wake Island, and American Samoa and any other foreign country. Foreign waterborne imports and exports statistics are derived primarily from data furnished to the U.S. Army Corps of Engineers by the Census Bureau and the U.S. Customs Service. Intransit statistics are derived primarily from data purchased from the Port Import Export Reporting Service, Inc. and supplemented by data provided by Customs and Census. Import and export shipments for the use of the United States Armed Forces abroad are not reported to the Waterborne Commerce Statistics Center (WCSC).

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.

Form EIA-812 (Energy Information Administration), Monthly Product Pipeline Report Form used to collect data on end-of-month stock levels and movements of petroleum products transported by pipeline. Intermediate movements for pipeline system operating in more than two Petroleum Administration for Defense Districts (PADDs) are included. Included are all product pipeline companies that carry petroleum products (including interstate, intrastate, and intracompany pipelines) in the 50 states and the District of Columbia. Approximately 80 respondents report on the Form EIA-812.

Form EIA-813, Monthly Crude Oil Report Form used to collect data on end-of-month stocks of crude oil held at pipeline and tank farms (associated with the pipelines) and terminals operated by the reporting company. Also, crude oil consumed by pipelines and on leases as pump fuel, boiler fuel, and so forth, is reported. Data are reported on a PADD basis and by all companies that carry or store 1,000 barrels or more of crude oil. Included in this survey are gathering and trunk pipeline companies (including interstate, intrastate, and intracompany pipelines), crude oil producers, terminal operators, storers of crude oil (except refineries), and companies transporting Alaskan crude oil by water in the 50 states and the District of Columbia. Approximately 175 respondents report on the Form EIA-183.

Frame Elements representing the subject population in a statistical study.


Gross Domestic Product (GDP) The net value of goods and services produced by labor and property in the United States, regardless of nationality of ownership.



Index Any series of numbers indicating quantitative changes over time in a given statistical aggregate (e.g., prices, costs), with reference to an arbitrary base (usually 100) that represents the status of the aggregate at a specified previous time or period.

In-house service When a firm uses its own assets and labor to transport its own products or inputs. In contrast to for-hire transportation service.

Input-output (I-O) analysis Analysis that breaks down the use of any given industry's outputs by consuming industries (including retail trade) and the sources of each industry's inputs by supplying industries.

Intermodal Transportation movements involving more than one mode, such as shipments of containers on truck and rail.

Intermodal traffic The movement of truck trailers or containers by rail and at least one other mode of transportation, usually trucks. (This has been the fastest growing rail segment over the past 10 years, although it does not account for a major part of traffic.)

Intermodal unit (rail) A trailer or container unit for intermodal traffic.

Internal/inland (maritime) Vessel movements (origin and destination) that take place solely on inland waterways. An inland waterway is located within the boundaries of the contiguous 48 states or within the boundaries of the State of Alaska.

Intransit merchandise (maritime) Merchandise coming into the United States from a foreign country and shipped to a foreign country without being recorded as an import.

Intraport (maritime) Movement of freight within the confines of a port whether the port has one or several arms or channels included in the port definition. This traffic type does not include car ferries and general ferries moving within a port. The term internal traffic also applies to these vessel movements: those that involve carriage on both inland waterways and Great Lakes; those occurring between offshore areas and inland waterways (e.g., oil rig supplies and fish); and those taking place within Delaware Bay, Chesapeake Bay, Puget Sound, and San Francisco Bay, which are considered internal bodies of water rather than arms of the ocean.

I-O (input-output) industry classification system System for classifying industries in the I-O accounts so that output typically represents the total output of all establishments in an industry. This system is based on the Standard Industrial Classification (SIC) or North American Industrial Classification System (NAICS). Both are adjusted to attain a common input structure for commodities produced by an I-O industry. The adjustments are referred to as redefinitions.




Lagging indicator Tends to follow fluctuations in GDPwhen GDP goes up, this measure ultimately goes up, and when GDP goes down, it tends to later decline. (See Coincident indicator and Leading indicator.)

Leading indicator Portends changes in GDP; that is, when this indicator goes up, GDP tends to go up some time later; when it goes down, GDP tends to eventually drop. (See Coincident indicator and Lagging indicator.)


Market data (aviation) Also referred to as on-flight origin-destination (O&D) data and summarizes passenger and freight data according to origin airport of enplanement and destination airport of deplanement.

Moving averages A method of smoothing a time series by averaging each successive group of data points. The moving averages method is a component of the ARIMA process.

Multimodal Referring to or incorporating multiple modes of transportation. Multimodal data are data that reflect activity in more than one mode of transportation.


National Income and Product Accounts (NIPA) Accounts of national economic production by industry, developed by the Bureau of Economic Analysis. They enable us to weight the different components of transportation by their relative weights in gross domestic product.

Navigable waters U.S. waters subject to the ebb and flow of the tide, and/or are presently used, or have been used in the past, or may be used to transport interstate or foreign commerce.

Nonsampling error, random On average and over time, values are as likely to be overestimated as they are to be underestimated. Therefore, over time, random errors do not bias the data but will likely give an inaccurate portrayal at any point in time. (See Nonsampling error, systematic and Sampling error.)

Nonsampling error, systematic A source of bias in data caused by the repetition of error patterns. (See Nonsampling error, random, and Sampling error.)


Outlier A data point located far from the rest of the data.

Output For the purposes of the TSI, the output of the transportation sector is equal to the economic value added of transportation carriers, that is, the difference between their revenues and the costs of their inputs. In the case of transit, total payroll is used as a proxy for economic value added.


Passenger-mile The movement of one passenger a distance of one mile.

Petroleum Administration for Defense Districts (PADDs) Geographic aggregations of the 50 states and the District of Columbia into five districts by the Petroleum Administration for Defense in 1950. These districts were originally defined during World War II for purposes of administering oil allocation.

Petroleum products Petroleum products are obtained from the processing of crude oil (including lease condensate), natural gas, and other hydrocarbon compounds. Petroleum products include unfinished oils, liquefied petroleum gases, pentanes plus, aviation gasoline, motor gasoline, naphtha-type jet fuel, kerosene-type jet fuel, kerosene, distillate fuel oil, residual fuel oil, petrochemical feedstocks, special naphthas, lubricants, waxes, petroleum coke, asphalt, road oil, still gas, and miscellaneous products.

Pipeline (petroleum) Crude oil and product pipelines used to transport crude oil and petroleum products respectively (including interstate, intrastate, and intracompany pipelines) within the 50 States and the District of Columbia.



Revenue freight ton-miles (aviation) One short ton (2,000 lb) of freight transported one mile by air.

Revenue passenger-miles (aviation) One revenue passenger transported one mile by air.


Sample In a statistical survey, a set of elements drawn from a population and analyzed to estimate the characteristics of the subject population.

Sampling error The difference between a sample estimate and a population value. (See Nonsampling error.)

Seasonally adjusted data A series of data points over time that are adjusted, using statistical techniques, to remove increases or decreases due to time of year. Also referred to as deseasonalized data.

Segment data (aviation) Summarizes information by nonstop portions of a flight.

Short ton A unit of weight equal to 2,000 pounds, in contrast to a metric ton (2,204.6 lb) .

Standard deviation A statistic used to measure the variation in a distribution. It is the square root of the variance. (See Variance.)


T-1 dataset The T-1 dataset includes information on all U.S. commercial air carriers, except air taxis. The dataset does not include foreign air carriers, entities that provide commercial services illegally, inhouse air transportation (e.g., corporate jets), general aviation, and air taxis.

T-2 dataset A quarterly summary of U.S. large certificated air carrier's monthly T-100 traffic and fuel data by carrier entity and aircraft type and across all airports.

T-3 dataset Also called the Quarterly U.S. Air Carrier Airport Activity Statistics, it summarizes large certificated carrier's monthly T-100 traffic data with supplemental information on civilian and military charters and all-cargo operations.

T-100 dataset The T-100 databases include data reported by U.S. carriers operating between airports located within the boundaries of the United States and its territories. These data fields contain information on passengers, freight, and/or mail enplaned at the origin airport and deplaned at the destination airport.

T-100f dataset A data system for foreign carriers to report their U.S. traffic, including foreign point of last departure for the United States and foreign point of first landing after the United States.

Ton-miles (maritime) For domestic movements, ton-miles equal the cargo tonnage multiplied by the distance between the point of loading on the water and point of unloading on the water. For U.S.Canada movements on the Great Lakes, ton-miles equal the tonnage multiplied by the distance between the U.S. and Canadian locations. For overseas imports and exports, foreign ton-miles are computed by multiplying the cargo tonnage by the miles carried on U.S. waterways and channels. Ton-miles are rounded to the nearest million.

Ton-miles (other than maritime) The movement of one ton of freight one mile.

Tonnage The physical weight of a transported commodity.

Train-mile The movement of a train a distance of one mile. Mileage measurement is not increased because of the presence of multiple locomotives in the train.


Unlinked passenger trips (transit) The number of passengers who board public transportation vehicles. Passengers are counted each time they board vehicles no matter how many vehicles they use to travel from their origin to their destination.

U.S. Class I railroad Railroads earning revenues of at least $289.4 million in 2004 , as defined by the Surface Transportation Board.


Value added Industry gross output less purchased materials and purchased services. Used together with input-output analysis.

Variance A measure of how spread out a distribution is. It is the sum of the squared deviations of n measurements from their mean divided by (n1).

Volume The total physical measure of transportation movement for a mode.


Weighted aggregate When different things are combined together to form a new category, such as putting apples and oranges together to be called fruit, the quantity of the new category often can not be measured as the sum of the quantities of its components because the components are measured in different units. One way to overcome this is to assign weights to the components, which puts the different units of the components on a comparable basis according to the relative importance of the components to the aggregate category. Weighted aggregate is the sum of the products of components' quantities multiplied with their corresponding weights.





Air Transport Association, About us? available at (link is external)as of January 2024.

American Trucking Associations, What is ATA? available at (link is external)as of January 2024.

The Association of American Railroads, About AAR Who is the AAR ? available at (link is external)as of January 2024.

Burlington Northern Santa Fe, Glossary of Railroad Terminology and Jargon, available at (link is external)as of January 2024.

The Conference Board, Glossary, available at (link is external)as of Dec. 23, 2003.

Mishken, Frederic S., The Economics of Money, Banking, and Financial Markets, 3rd Edition, Mishken Economics, Inc. (New York: 1992).

Sweeney, Dennis J., David R. Anderson, and Thomas A. Williams, Quantitative Methods for Business, 7th Edition, South-Western College Publishing (Cincinnati, OH: 1998).

U.S. Department of Commerce, Bureau of Economic Analysis, Glossary Index, available at (link is external)as of Dec. 23, 2003.

U.S Department of Energy, Energy Information Administration, Petroleum Supply Monthly, available at (link is external) as of January 2024.

U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Statistics Annual Report 2001, BTS02-07 (Washington, DC: 2002).

U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Expressions 1996 (Washington, DC: 1996).

Webster Comprehensive Dictionary, Encyclopedic Edition, Volume One, J.G. Ferguson Publishing Co. (Chicago, IL: 1988).

Webster's II New College Dictionary. Houghton Mifflin Co. (Boston, MA: 1999).