Intermodal is a term that refers to more than one mode of transport. For example, passenger stations which provides 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 using containers is that it reduces cargo handling, and so improves security, reduces damages and loss, and allows freight to be transported faster
History
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 aeroplanes. Because no freight handling was required, fewer personnel were required and loading times were decreased.
Truck trailers were first carried by railway after World War II, an arrangement often called "piggyback". The Canadian Pacific Railway was a pioneer in piggyback transport, becoming the first North American railway to introduce the service in 1952.
In the United States of America, rail intermodal traffic tripled between 1980 and 2002, according to the Association of American Railroads, from 3.1 million trailers and containers to 9.3 million.
Equipment
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 wide by eight feet six inches high. Their length is usually either 20 feet, 40 feet, or 45 feet, although other lengths exist. They are made out of steel and can be stacked on top of each other. They can be carried by truck, rail, container ship, or aeroplane.
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, 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.
A newer method of transporting trailers has been developed by Road-Railer 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.
Vehicles
In North America, containers are often shipped by rail in well cars. These cars resemble flatcars but have a container-sized depression, or well, in the middle of the car. This depression allows for sufficient clearance to allow two containers to be loaded in the car, one on top of the other. In Europe, stricter railway height restrictions prohibit containers from being stacked two high, and containers are hauled one high either on standard flatcars or other rail cars.
