During an intermediate phase of the conversion of the Port Pirie to Marree railway from a narrower gauge 1,067 mm (3 ft 6 in) to a standard gauge, train lengths of standard gauge flat wagons were fitted with narrow gauge rails, to allow a narrow gauge coal trains to by pass the difficult Flinders Ranges then affected by washaways.
The rails on the lower wagons were continuous, so that the upper train was moved on and off in one piece.
The narrower gauge air brakes were connected to the standard gauge train's air brakes, to allow some flexing around curves. The narrower gauge train was also coupled to a buffer stop at one end of the standard gauge train.
A short ramp was installed to raise the narrow gauge trains about a metre onto the deck of the standard gauge train. There were no tight overbridges (overpasses) or tunnels to restrict operation of these double deck trains.
The standard gauge track was in this instance brand new and of a heavier standard with gentler curves and gradients than the narrow gauge track it replaced, so it is not clear whether a narrow gauge train could have transported a standard gauge train in reverse. It is noted that with a Weltrol well wagon, the load has to be lifted on and off by a crane one at a time, which is much slower.
With the transporter train, the loading gauge of the narrow gauge train under tunnels and overbridges needs to be about a metre taller than would otherwise be the case to allow for the height of the floor of the flat waggons and the rails thereupon.
The transporter train operated for about a year until the new standard gauge line to Leigh Creek was completed. The maximum speed of the piggyback train is unclear.