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Intermodal freight transport

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An intermodal train carrying both shipping containers and highway semi-trailers in "piggyback" service, on flatcars, passes through the Cajon Pass in February, 1995.
An intermodal train carrying both shipping containers and highway semi-trailers in "piggyback" service, on flatcars, passes through the Cajon Pass in February, 1995.

Intermodal is a term that refers to more than one mode of transport. For example, passenger stations which provide transfers between buses and trains are described as intermodal (see: intermodal passenger transport). This article describes intermodal as applied to the transportation of freight in a container or vehicle, using multiple modes of transportation (rail, ocean carrier, and truck), without any handling of the freight itself when changing modes. The advantage of utilizing this method is that it reduces cargo handling, and so improves security, reduces damages and loss, and allows freight to be transported faster.



Pallets made their first major appearance during World War II, when the United States military assembled freight on pallets, allowing fast transfer between warehouses, trucks, trains, ships, and aircraft. Because no freight handling was required, fewer personnel were required and loading times were decreased.

Truck trailers were first carried by railway before World War II, an arrangement often called "piggyback", by the small Class I railroad, the Chicago Great Western in 1936. The Canadian Pacific Railway was a pioneer in piggyback transport, becoming the first major North American railway to introduce the service in 1952.

While rudimentary freight containers, then known as lift vans, were used in the United States as early as 1911, it was not until the 1950s that containers started to revolutionize freight transportation. One pioneering railway was the White Pass and Yukon Route, who acquired the world's first container ship, the Clifford J. Rogers, built in 1955, and introduced containers to its railway in 1956. Starting in the 1960s the use of containers increased steadily. Standards for containers were issued by the International Organization for Standardization (ISO) between 1968 and 1970, ensuring interchangeability between different modes of transportation worldwide. The containers became known as ISO containers for this reason.

In the United States of America, rail intermodal traffic tripled between 1980 and 2002 according to the Association of American Railroads (AAR), from 3.1 million trailers and containers to 9.3 million.

Origins of double-stacked container transport in USA

Intermodal ship-to-rail transfer of containerized cargos at the Port in Long Beach, California.
Intermodal ship-to-rail transfer of containerized cargos at the Port in Long Beach, California.

The introduction of double-stack rail technology in 1984 — which could never have occurred without the advent of containerization — has been one of the boldest and most productive applications of containerization imaginable. It has changed the entire intermodal freight distribution industry in North America forever; it has resulted in more cost-effective, secure, and reliable freight shipments, and provided domestic intermodal rail capacity that could not otherwise have been possible.

The double-stack rail car's unique design also significantly reduced damage in transit, and provided greater cargo security by cradling the lower containers so their doors cannot be opened. And a succession of large, new domestic container sizes was introduced to further enhance shipping productivity for customers. As early as the 1970s, doublestack designs and equipment were introduced, but the cars were heavy and uneconomical to operate.

While always deflecting credit to the many contributors who enabled the introduction of Stacktrain rail service, the chief executive of Pacer International, Inc. (Concord CA), Don Orris, is widely considered the "Father of Stacktrain Service." He earned that moniker for his role in the early 1980s, as the head of APL's intermodal department, in sponsoring the development and implementation of lightweight, fuel-efficient equipment and the first successful operating network.

With this system, launched in 1984, container trains were finally able to break cost, capacity and service barriers by using specially engineered rail cars that could carry two tiers of containers instead of one -- significantly reducing the locomotive power, track capacity and train crews required by conventional intermodal trains to move a comparable payload.

In 1999, Pacer International acquired the original double-stack network that Don and his colleagues had helped develop, and named it Pacer Stacktrain. Pacer remains the largest wholesale provider of double-stack rail service in North America, and now carries (2006) more than one million containers per year. The company accounts for more than 20 percent of all domestic container moves in North America. Overall, the double-stack market has grown more than 100-fold since 1984, and now accounts for about 70 percent of intermodal shipments.


Containers, also known as intermodal containers or as ISO containers because the dimensions have been defined by the ISO, are the main type of equipment used in intermodal transport, particularly when one of the modes of transportation is by ship. Containers are eight feet (2438 mm) wide by eight feet (2438 mm) high. Since introduction, there have been moves to adopt other heights, such as eight feet six inches (2591 mm), nine feet six inches (2896 mm) and ten feet six inches (3200 mm). The most common lengths are 20 feet (6096 mm), 40 feet (12192 mm), 48 feet (14630 mm) and 53 feet (16154 mm), although other lengths exist. They are made out of steel and can be stacked on top of each other (a popular term for a two-high stack is "double stack"). On ships they are typically stacked up to seven units high. They can be carried by truck, rail, container ship, or aeroplane. When carried by rail, containers can be loaded on flatcars or in container well cars. In Europe, stricter railway height restrictions (smaller loading gauge and structure gauge) prohibit containers from being stacked two high, and containers are hauled one high either on standard flatcars or other railroad cars.

A portion of a "double stack" container train operated by Pacer Stacktrain
A portion of a "double stack" container train operated by Pacer Stacktrain

Some variations on the standard container exist. Open-topped versions covered by a fabric curtain are used to transport larger loads. A container called a "tanktainer," consisting of a tank fitted inside a standard container frame, allows liquids to be carried. Refrigerated containers are used for perishables. There is also the swap body, which is typically used for road and rail transport, as they are built too lightly to be stacked. They have folding legs under their frame so that they can be moved between trucks without using a crane.

Truck trailers are often used for freight that is transported primarily by road and rail. Typically, regular semi-trailers can be used, and do not need to be specially designed. When travelling by rail, semi-trailers are transported on railway flatcars, an arrangement called "piggyback."

In North America, containers are often shipped by rail in container well cars. These cars resemble flatcars but the newer ones have a container-sized depression, or well, in the middle (between the bogies or "trucks") of the car. This depression allows for sufficient clearance to allow two containers to be loaded in the car in a "double stack" arrangement. The newer container cars also are specifically built as a small articulated "unit", most commonly in components of three or five, whereby two components are connected by a single bogie as opposed to two bogies, one on each car (The photo above under "Equipment" shows an example of the new setup.) Double stacking is also used in parts of Australia. A newer method of transporting trailers has been developed by RoadRailer Corporation, which is owned by Norfolk Southern Railway. When the trailers are transported on rail, railway wheel assemblies are placed between the trailers, in effect turning the trailers into one large articulated railway car. This method is faster than carrying trailers on flatcars and requires no extra railway cars, but the trailers need to be specially designed (strengthened).

Container ships

The 300-meter-long container ship CMA CGM Balzac
The 300-meter-long container ship CMA CGM Balzac

Container ships are used to transport containers by sea. These vessels are custom-built to hold containers. Some vessels can hold thousands of containers. Their capacity is often measured in TEU or FEU. These initials stand for "twenty feet equivalent unit," and "forty feet equivalent unit," respectively. For example, a vessel that can hold 1,000 40-foot containers or 2,000 20-foot containers can be said to have a capacity of 1,000 FEU or 2,000 TEU. In the year 2005, the largest container ships in regular operation are registered to carry in excess of 8,000 TEUs.

See also

Look up Intermodal freight transport in
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  • DeBoer, David J. (1992). Piggyback and Containers: A History of Rail Intermodal on America's Steel Highway. Golden West Books, San Marino, CA. ISBN 0-87095-108-4.

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