A road train is a trucking concept used in remote areas of Argentina, Australia, Mexico, the United States and Canada to move freight efficiently. The term 'road train' is most often used in Australia. In the U.S. and Canada the terms 'triples,' 'turnpike doubles' and 'Rocky Mountain doubles' are commonly used for longer combination vehicles. A road train consists of a relatively conventional tractor unit, but instead of pulling one trailer or semi-trailer, a road train pulls two or more of them.
Here are pictures of some huge off-highway road trains.