Watson, South Australia

Looking east on the Trans-Australia Railway from Cook, South Australia
Track gauge	1,435 mm (4 ft 8 1⁄2 in)

The Trans-Australian Railway crosses the Nullarbor Plain of Australia from Port Augusta in South Australia to Kalgoorlie in Western Australia. It includes a 478 kilometres (297 mi) stretch of dead-straight track, the world's longest, between the 797 km (495 mi) post west of Ooldea and the 1,275 km (792 mi) post west of Loongana.

The line forms an important freight route between Western Australia and the eastern states. Currently two passenger services also use the line, the Indian Pacific for its entire length and The Ghan between Port Augusta and Tarcoola.

Earlier passenger services on the route were known as the Great Western Express.

In 1901, the six Australian colonies federated to form the Commonwealth of Australia. At that time, Perth, the capital of Western Australia, was isolated from the remaining Australian States by thousands of miles of desert terrain and the only practicable method of transport was by sea, a time-consuming, inconvenient and often uncomfortable voyage across the Great Australian Bight, a stretch of water known for rough seas. One of the inducements held out to Western Australians to join the new federation was the promise of a federally funded railway line linking Western Australia with the rest of the continent.

In 1907 legislation was passed, allowing for the route to be surveyed. The survey was completed in 1909 and proposed a route from Port Augusta (the existing railhead at the head of Spencer Gulf in South Australia's wheatfields) via Tarcoola to the gold mining centre of Kalgoorlie in Western Australia, a distance of 1063 miles (1711 km). The line was to be to the standard gauge of 4 ft 8 ¹⁄₂ in (1,435 mm), even though the state railway systems at both ends were narrow gauge at the time. Its cost was estimated at £4,045,000.