Truck & Bus Forum - Wagon train.

http://www.youtube.com/watch?v=VVwTnJFRj5Q

Quote:

Roadrailers first appeared on American railroads in the 1950s. The trailers were built with integrated railroad wheelsets that could be lowered into position when the trailer was pulled behind a train. More modern roadrailers do not include integrated railroad wheels, but ride on specially-manufactured bogies that do double-duty, serving as articulation points between multiple trailers in a train. Each truck is equipped with two fifth wheels and at one end (or both ends) of a convoy there is an adaptor truck equipped with one fifth wheel and one regular AAR Type "E" or Type "F" automatic coupler. Each semi-trailer has one king pin at each end. Because the bogie is significantly lighter than a rail flatcar or well-car, roadrailer freight trains are much lighter and therefore are more energy efficient than traditional intermodal trains.