double stack

Double-stack rail transport is a form of intermodal freight transport where intermodal containers are stacked two high on railroad cars. Introduced in North America in 1984, double stack has become increasingly common there, being used for nearly 70% of United States intermodal shipments. Using double stack technology, a freight train of a given length can carry roughly twice as many containers, sharply reducing costs per container. On most North American railroads, special well cars are used for double-stack to reduce the needed vertical clearance and to lower the center of gravity of a loaded car. In addition, the well car design significantly reduces damage in transit and provides greater cargo security by cradling the lower containers so their doors cannot be opened. A succession of larger container sizes have been introduced to further increase shipping productivity on shipments within North America.
Double-stack rail operations are growing in other parts of the world, but are often constrained by clearance and other infrastructure limitations.

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