Office of Operations Freight Management and Operations

Freight and Air Quality Handbook

Glossary of Terms

Air Pollutant – Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. They may be in the form of solid particles, liquid droplets, gases, or in combination thereof. Generally, they fall into two main groups (1) those emitted directly from identifiable sources and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation. Air pollutants are often grouped in categories for ease in classification; some of the categories are solids, sulfur compounds, volatile organic chemicals, particulate matter, nitrogen compounds, oxygen compounds, halogen compounds, radioactive compound, and odors.

Air Pollution – The presence of contaminants or pollutant substances in the air that interfere with human health or welfare, or produce other harmful environmental effects.

Air Toxics – Any air pollutant for which a national ambient air quality standard (NAAQS) does not exist (i.e. excluding ozone, carbon monoxide, PM10, sulfur dioxide, nitrogen oxide) that may reasonably be anticipated to cause cancer; respiratory, cardiovascular, or developmental effects; reproductive dysfunctions, neurological disorders, heritable gene mutations, or other serious or irreversible chronic or acute health effects in humans.

Airborne Particulates – Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets. Chemical composition of particulates varies widely, depending on location and time of year. Sources of airborne particulates include dust, emissions from industrial processes, combustion products from the burning of wood and coal, combustion products associated with motor vehicle or non-road engine exhausts, and reactions to gases in the atmosphere.

Arterial – Major streets or highways, many with multilane or freeway design, serving high-volume traffic corridor movements that connect major generators of travel. While they may provide access to abutting land, their primary function is to serve traffic moving through the area.

Attainment Area – A geographic area in which levels of a criteria air pollutant meet the health-based primary standard (national ambient air quality standard, or NAAQS) for the pollutant. An area may have on acceptable level for one criteria air pollutant, but may have unacceptable levels for others. Thus, an area could be both attainment and nonattainment at the same time. Attainment areas are defined using federal pollutant limits set by regulatory agencies.

Backhaul – The process of a transportation vehicle (typically a truck) returning from the original destination point to the point of origin. A backhaul can be with a full or partially loaded trailer.

Barge – The cargo-carrying vehicle that inland water carriers primarily use. Basic barges have open tops, but there are covered barges for both dry and liquid cargoes.

Belly Cargo – Air freight carried in the belly of passenger aircraft.

Bottleneck – A section of a highway or rail network that experiences operational problems such as congestion. Bottlenecks may result from factors such as reduced roadway width or steep freeway grades that can slow trucks.

Breakbulk Cargo – Cargo of non-uniform sizes, often transported on pallets, sacks, drums, or bags. These cargoes require labor-intensive loading and unloading processes. Examples of breakbulk cargo include coffee beans, logs, or pulp.

Bulk Cargo – Cargo that is unbound as loaded; it is without count in a loose unpackaged form. Examples of bulk cargo include coal, grain, and petroleum products.

Cabotage – A national law that requires costal and intercostal traffic to be carried in its own nationally registered, and sometimes built and crewed ships.

Capacity – The physical facilities, personnel and process available to meet the product of service needs of the customers. Capacity generally refers to the maximum output or producing ability of a machine, a person, a process, a factory, a product, or a service.

Carbon Dioxide (CO2) – A naturally occurring gas fixed by photosynthesis into organic matter. A by-product of fossil fuel combustion and biomass burning, it is also emitted from land-use changes and other industrial processes.

Carbon Monoxide (CO) – A colorless, odorless, poisonous gas, produced by incomplete burning of carbon-based fuels, including gasoline, oil, and wood. When carbon monoxide gets into the body, the carbon monoxide combines with chemicals in the blood and prevents the blood from bringing oxygen to cells, tissues, and organs. High-level exposures to carbon monoxide can cause serious health effects, with death possible from massive exposures. Symptoms of exposure to carbon monoxide can include vision problems, reduced alertness, and general reduction in mental and physical functions. Carbon monoxide exposures are especially harmful to people with heart, lung, and circulatory system diseases.

Carload – Quantity of freight (in tons) required to fill a railcar; amount normally required to qualify for a carload rate.

Carrier – A firm which transports goods or people via land, sea, or air.

Catalytic Converter – An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen.

Chassis – A trailer-type device with wheels constructed to accommodate containers, which are lifted on and off.

Class I Railroad – Railroads which have annual gross operating revenues over $266.7 million.

Class II Railroad – See Regional Railroad.

Class III Railroad – See Shortline Railroad.

Clean Air Act – Originally passed in 1963, although the 1970 version of the law is the basis of today's U.S. national air pollution program. The 1990 Clean Air Act Amendments are the most far-reaching revisions of the 1970 law, and are usually referred to as the 1990 Clean Air Act.

Climate Change (also referred to as "global climate change") – A change in the mean state or variability of the climate, whether due to natural variability or as a result of human activity, that persists for an extended period, typically decades or more. In some cases, "climate change" has been used synonymously with the term "global warming"; scientists however, tend to use the term in the wider sense to also include natural changes in climate.

Coastal Shipping – Also known as short-sea or coastwise shipping, describes marine shipping operations between ports along a single coast or involving a short sea crossing.

Combustion – Burning of fuels such as coal, oil, gas, and wood. Many important pollutants, such as sulfur dioxide, nitrogen oxides, and particulates (PM-10) are combustion products.

Commodity – An item that is traded in commerce. The term usually implies an undifferentiated product competing primarily on price and availability.

Common Carrier – Any carrier engaged in the interstate transportation of persons/property on a regular schedule at published rates, whose services are for hire to the general public.

Concentration – The relative amount of a substance mixed with another substance. Examples are 5 parts per million (ppm) of carbon monoxide in air.

Conformity – A process in which transportation plans and spending programs are reviewed to ensure they are consistent with federal clean air requirements; transportation projects collectively must not worsen air quality.

Container – A "box" typically ten to forty feet long, which is used primarily for ocean freight shipment. For travel to and from ports, containers are loaded onto truck chassis' or on railroad flatcars.

Container on Flatcar (COFC) – Containers resting on railway flatcars without a chassis underneath.

Containerization – A shipment method in which commodities are placed in containers, and after initial loading, the commodities per se are not re-handled in shipment until they are unloaded at destination.

Containerized Cargo – Cargo that is transported in containers that can be transferred easily from one transportation mode to another.

Criteria Air Pollutants – The 1970 amendments to the Clean Air Act required EPA to set National Ambient Air Quality Standards for certain pollutants known to be hazardous to human health. EPA has identified and set standards to protect human health and welfare for six pollutants ozone, carbon monoxide, total suspended particulates, sulfur dioxide, lead, and nitrogen oxide. The term, "criteria pollutants" derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants. It is on the basis of these criteria that standards are set or revised.

Deadhead – The return of an empty transportation container back to a transportation facility. Commonly-used description of an empty backhaul.

Distribution Center (DC) – The warehouse facility which holds inventory from manufacturing pending distribution to the appropriate stores.

Dock – A space used or receiving merchandise at a freight terminal.

Double-Stack – Railcar movement of containers stacked two high.

Drayage – Transporting of rail or ocean freight by truck to an intermediate or final destination; typically a charge for pickup/delivery of goods moving short distances (e.g., from marine terminal to warehouse).

Emission – Release of pollutants into the air from a source.

Emission Factor – The relationship between the amount of pollution produced and the amount of fuel consumed.

Emission Inventory – A listing, by source, of the amount of air pollutants discharged into the atmosphere of a community; used to establish emission standards.

Exhaust Gas Recirculation System (EGR) – The controlled diversion of some of the combustion gases back into the combustion chamber, lowering the combustion temperature and reducing nitrogen oxides in the engine. This is a very effective process, because oxides of nitrogen tend to rise disproportionately with increased combustion temperatures. There are two methods of exhaust gas recirculation: internally through overlap of valve opening times and externally with recirculation valves and manifolds.

Fossil Fuel – Fuel derived from ancient organic remains; e.g. peat, coal, crude oil, and natural gas.

Fuel Cell – An electrochemical engine (no moving parts) that converts the chemical energy of a fuel, such as hydrogen, and an oxidant, such as oxygen, directly to electricity. The principal components of a fuel cell are catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes.

Greenhouse Effect – The process by which the absorption of infrared radiation by the atmosphere warms the Earth. In common parlance, the term "greenhouse effect" may be used to refer either to the natural greenhouse effect, due to naturally occurring greenhouse gases, or to the enhanced (anthropogenic, or man-made) greenhouse effect, which results from gases emitted by human activities.

Greenhouse Gas – A gas, whether natural or man-made, that contributes to the greenhouse effect by absorbing and emitting radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth's surface, atmosphere, and clouds. Greenhouse gases include water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), ozone (O3), hydrofluorocarbons (HFC), and others.

Gross Vehicle Weight (GVW) – The combined total weight of a vehicle and its freight.

Hazardous Air Pollutants (HAPs) – Chemicals that cause serious health and environmental effects. Health effects include cancer, birth defects, and nervous system problems. HAPs are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, etc.).

Hydrocarbons (HC) – Chemical compounds that consist entirely of carbon and hydrogen.

Intermodal Terminal – A location where links between different transportation modes and networks connect. Using more than one mode of transportation in moving persons and goods. For example, a shipment moved over 1,000 miles could travel by truck for one portion of the trip, and then transfer to rail at a designated terminal.

Just-in-Time (JIT) – Cargo or components that must be at a destination at the exact time needed. The container or vehicle is the movable warehouse.

Laker – Large commercial ship operating on the Great Lakes carrying bulk cargo The Lakers are up to 1,000 feet long and can carry up to 66,000 tons of cargo. The large bulk Lakers stay within the Great Lakes because they are too large to enter the Saint Lawrence Seaway portion.

Lead (Pb) – A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Less-Than-Containerload/Less-Than-Truckload (LCL/LTL) – A container or trailer loaded with cargo from more than one shipper; loads that do not by themselves meet the container load or truckload requirements.

Level of Service (LOS) – A qualitative assessment of a road’s operating conditions. For local government comprehensive planning purposes, level of service means an indicator of the extent or degree of service provided by, or proposed to be provided by, a facility based on and related to the operational characteristics of the facility. Level of service indicates the capacity per unit of demand for each public facility.

Lift-on/Lift-off (lo/lo) Cargo – Containerized cargo that must be lifted on and off vessels and other vehicles using handling equipment.

Line Haul – The movement of freight over the road/rail from origin terminal to destination terminal, usually over long distances.

Liquid Bulk Cargo – A type of bulk cargo that consists of liquid items, such as petroleum, water, or liquid natural gas.

Logistics – All activities involved in the management of product movement; delivering the right product from the right origin to the right destination, with the right quality and quantity, at the right schedule and price.

Methane – A colorless, nonpoisonous, flammable gas created by anaerobic decomposition of organic compounds. It is the main component of natural gas and is a greenhouse gas.

Mobile Sources – Moving objects that release pollution; mobile sources include cars, trucks, buses, planes, trains, motorcycles, and gasoline-powered lawn mowers. Mobile sources are divided into two groups: on-road vehicles, which include cars, trucks and buses, and nonroad vehicles, which includes trains, planes, lawn mowers, and some portable equipment.

Neo-bulk Cargo – Shipments consisting entirely of units of a single commodity, such as cars, lumber, or scrap metal.

Nitric Oxide (NO) – A gas formed by combustion under high temperature and high pressure in an internal combustion engine. NO is converted by sunlight and photochemical processes in ambient air to nitrogen oxide. NO is a precursor of ground-level ozone pollution, or smog.

Nitrogen Dioxide (NO2) – The result of nitric oxide combining with oxygen in the atmosphere; major component of photochemical smog.

Nitrogen Oxides (NOx) – A criteria air pollutant. Nitrogen oxides are produced from burning fuels, including gasoline and coal. Nitrogen oxides are smog formers, which react with volatile organic compounds to form smog. Nitrogen oxides are also major components of acid rain.

Nonattainment Area – A geographic area in which the level of a criteria air pollutant is higher than the level allowed by the federal standards. A single geographic area may have acceptable levels of one criteria air pollutant but unacceptable levels of one or more other criteria air pollutants; thus, an area can be both attainment and nonattainment at the same time.

On-dock Rail – Direct shipside rail service. Includes the ability to load and unload containers/breakbulk directly from rail car to vessel.

Owner-operator – Trucking operation in which the owner of the truck is also the driver.

Ozone – A gas composed of three oxygen atoms bound together into an ozone molecule (O3). Ozone occurs in nature; it produces the sharp smell you notice near a lightning strike. High concentrations of ozone gas are found in a layer of the atmosphere – the stratosphere – high above the Earth. Stratospheric ozone shields the Earth against harmful rays from the sun, particularly ultraviolet B. Smog's main component is ozone; this ground-level ozone is a product of reactions among chemicals produced by burning coal, gasoline and other fuels, and chemicals found in products including solvents, paints, hairsprays, etc.

Particulates; Particulate Matter – A criteria air pollutant. Particulate matter includes dust, soot and other tiny bits of solid materials that are released into and move around in the air. Particulates are produced by many sources, including burning of diesel fuels by trucks and buses, incineration of garbage, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining operations, agricultural burning (field and slash burning), and operation of fireplaces and woodstoves. Particulate pollution can cause eye, nose and throat irritation, heart and lung disease, increased respiratory symptoms and disease, decreased lung function, and premature death.

Parts Per Billion (ppb)/Parts Per Million (ppm) – Units commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in water, land, or air.

Payload – The cargo carried in a vehicle exclusive of the vehicle itself.

Piggyback – A rail/truck service. A shipper loads a highway trailer, and a carrier drives it to a rail terminal and loads it on a flatcar; the railroad moves the trailer-on-flatcar combination to the destination terminal, where the carrier offloads the trailer and delivers it to the consignee.

PM10/PM2.5 PM10 is measure of particles in the atmosphere with a diameter of less than or equal to 10 micrometers. PM2.5 is a measure of particles less than or equal to 2.5 micrometers in diameter. Therefore, PM10 includes PM2.5.

Pool/Drop Trailers – Trailer that are staged at a facilities for preloading purposes.

Port Authority – State or local government that owns, operates, or otherwise provides wharf, dock, and other terminal investments at ports.

Radio Frequency (RFID) – A form of wireless communication that lets users relay information via electronic energy waves from a terminal to a base station, which is linked in turn to a host computer. The terminals can be placed at a fixed station, mounted on a forklift truck, or carried in the worker's hand. The base station contains a transmitter and receiver for communication with the terminals. When combined with a bar-code system for identifying inventory items, a radio-frequency system can relay data instantly, thus updating inventory records in so-called "real time."

Rail Siding – A very short branch off a main railway line with only one point leading onto it. Sidings are used to allow faster trains to pass slower ones or to conduct maintenance. Reefer Trailer – A refrigerated trailer that is commonly used for perishable goods.

Regional Railroad – Railroad defined as line-haul railroad operating at least 350 miles of track and/or earns revenue between $40 million and $266.7 million.

Reliability – Refers to the degree of certainty and predictability in travel times on the transportation system. Reliable transportation systems offer some assurance of attaining a given destination within a reasonable range of an expected time. An unreliable transportation system is subject to unexpected delays, increasing costs for system users.

Roll-on/Roll-off (ro/ro) Cargo – Wheeled cargo, such as automobiles, or cargo carried on chassis that can be rolled on or off vehicles without using cargo handling equipment.

Short Line Railroad – Freight railroads which are not Class I or Regional Railroads, that operate less than 350 miles of track and earn less than $40 million.

Short-sea Shipping – Also known as coastal or coastwise shipping, describes marine shipping operations between ports along a single coast or involving a short sea crossing.

Smog – A mixture of pollutants, principally ground-level ozone, produced by chemical reactions in the air involving smog-forming chemicals. A major portion of smog-formers comes from burning of petroleum-based fuels such as gasoline. Other smog-formers, volatile organic compounds, are found in products such as paints and solvents. Smog can harm health, damage the environment and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic, sunshine, high temperatures and calm winds or temperature inversion (weather condition in which warm air is trapped close to the ground instead of rising). Smog is often worse away from the source of the smog-forming chemicals, since the chemical reactions that result in smog occur in the sky while the reacting chemicals are being blown away from their sources by winds.

State Implementation Plan (SIP) – A detailed description of the programs a state will use to carry out its responsibilities under the Clean Air Act. State implementation plans are collections of the regulations used by a state to reduce air pollution in nonattainment areas. The Clean Air Act requires that EPA approve each state implementation plan. Members of the public are given opportunities to participate in review and approval of state implementation plans.

Sulfur Dioxide – A criteria air pollutant and gas produced by burning sulfur-containing fuels. Coal combustion (particularly for power plants) is the largest source, but it is also produced by paper production, metal smelting, and diesel fuel combustion. Sulfur dioxide is closely related to sulfuric acid, a strong acid. Sulfur dioxide plays an important role in the production of acid rain.

Switching and Terminal Railroad – Railroad that provides pick-up and delivery services to line-haul carriers.

Temperature Inversion – One of the weather conditions that are often associated with serious smog episodes in some portions of the country. In a temperature inversion, air does not rise because it is trapped near the ground by a layer of warmer air above it. Pollutants, especially smog and smog-forming chemicals, including volatile organic compounds, are trapped close to the ground.

Throughput – Total amount of freight imported or exported through a seaport measured in tons or TEUs.

Ton-mile – A measure of output for freight transportation; reflects weight of shipment and the distance it is hauled; a multiplication of tons hauled by the distance traveled. One ton of cargo transported one mile equals one ton-mile.

Trailer on Flatcar (TOFC) – Transport of trailers with their loads on specially designed rail cars.

Transloading – Transferring bulk shipments from the vehicle/container of one mode to that of another at a terminal interchange point.

Transshipment – Transferring any shipments from the vehicle/container of one mode to that of another at a terminal interchange point.

Truckload (TL) – Quantity of freight required to fill a truck, or at a minimum, the amount required to qualify for a truckload rate.

Twenty-foot Equivalent Unit (TEU) – The standard measure used for containerized cargo. The amount of cargo that would fill an eight-foot by eight-foot by 20-foot intermodal container.

Unit Train – A train of a specified number of railcars handling a single commodity type which remain as a unit for a designated destination or until a change in routing is made.

Vehicle Miles of Travel (VMT) – Each mile traveled by vehicle without regard to the contents of the vehicle. For example, a five-mile truck trip would generate five vehicle miles of travel.

Volatile Organic Compounds (VOCs) – Chemicals that produce vapors readily. At room temperature and normal atmospheric pressure, vapors escape easily from volatile liquid chemicals. Volatile organic chemicals include gasoline, industrial chemicals such as benzene, solvents such as toluene and xylene, and tetrachloroethylene (perchloroethylene, the principal dry cleaning solvent). Many volatile organic chemicals are also hazardous air pollutants; for example, benzene causes cancer.

Weigh-in-Motion – Defined by the American Society for Testing and Materials (ASTM) as "the process of measuring the dynamic tire forces of a moving vehicle and estimating the corresponding tire loads of the static vehicle." It allows truck weights to be determined without requiring the vehicle to stop.

Previous Section | Next Section | Top
Office of Operations