Under the provisions of the "Northern Territory Acceptance Act 1910", the Commonwealth Railways assumed responsibility for the South Australian Railways' narrow gauge lines in the far north of South Australia and the Northern Territory. The Act mandated the building of a south–north railway although, crucially, no date was specified. Two routes were considered: a standard gauge line branching off the Trans-Australian Railway at Tarcoola or a cheaper extension, from Oodnadatta, of the narrow gauge Central Australia Railway (CAR) line that had opened in 1891. Eventually the latter was chosen, and the extension to Alice Springs was opened in 1929. Meanwhile, the North Australia Railway (NAR) opened in stages south from Darwin to Birdum, the latter being reached in 1929.