Temporary Way
The Permanent Way is so called because there is often a "Temporary Way" used for construction purposes and which is replaced by the "Permanent Way" when construction of the right of way nears completion.
The actual gauge of this temporary way is poorly documented, but it would generally be narrower than the permanent gauge.
In restricted spaces such as tunnels, the temporary way might be double track, even though the tunnel will ultimately be single track. Thus the Airport Rail Link in Sydney had construction trains of 900 mm (2 ft 11 7⁄16 in) gauge which were replaced by the permanent tracks of 1,435 mm (4 ft 8 1⁄2 in) gauge.
The narrower the temporary way, the quicker it can be built. During World War II, it was proposed to expedite a Yunnan-Burma railway using a tiny "toy" 1 ft 3.3in gauge, since such a small gauge can have the tightest of curves in difficult terrain.
The professional body for track designers and installers is called the Permanent Way Institution.
Read more about this topic: Track Gauge
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