Concept
Piggyback transportation refers to the transportation of goods where one transportation unit is carried on the back of something else. It is a specialised form of intermodal transportation and combined transport. Piggyback is a corruption of pickaback, which is likely to be a folk etymology alteration of pick pack (1560s), which perhaps is from pick, a dialectal variant of the verb pitch. Trailer-on-flatcar Rolling highwayModalohrRoadrailerWell carClass U special wagon#Intermodal container well wagonsWell wagon and Loading gauge In rail transport, the practice of carrying trailers or semi-trailers in a train atop a flatcar is referred to as "piggybacking". Early drawings of the Liverpool & Manchester Railway c1830 show road coaches being piggybacked on railway flat wagons. The rail service provided for trucks which are carried on trains for part of their journey is referred to as a rolling road, or rolling highway. A related transportation method is the rail transport of semi-trailers, without road tractors, sometimes referred to as "trailer on flatcar (TOFC)". In the United States, TOFC traffic grew from 1% of freight in 1957 to 5% in 1964 and 15% in 1986. A railway wagon of one track gauge can be carried on a flat wagon (transporter wagon or rollbock) of another gauge. In addition, an entire train of coupled wagons of one gauge can be carried on continuous rails on a train of flat wagons of another gauge. This was achieved by the Commonwealth Railways on the Marree railway line in South Australia between Telford Cut and Port Augusta in the mid-1950s. Japan Railways planned a similar "Train on Train" scheme, but at much higher speeds, to operate from 2016. Small ships of all kinds can be piggybacked on larger ships. Examples include lifeboats, landing craft, and minesweepers on motherships, as well as midget submarines on larger submarines, such as those used for the 1942 Japanese submarine attack on Sydney.
