By the later half of the 20th century, many of these lines and branches were closed effectively shrinking Adelaide's rail system into a sparse size.

The Department for Infrastructure & Transport (DIT) owns the suburban passenger rail network, comprising seven lines originating from Adelaide railway station on North Terrace in the CBD.

The ARTC network extends from Adelaide towards Melbourne, Sydney, Perth and Darwin and is used by substantial interstate freight traffic.

They were a handful of lines that were used mainly to move bulk grain and stone from the Barossa Valley and mid-north region of the state to the Port Adelaide area.

[8] Journey Beyond is a private company operating long-distance interstate passenger trains on the ARTC's standard gauge lines, and run from the Adelaide Parklands Terminal, just west of the CBD.

Journey Beyond's trains are the Indian Pacific to Sydney and Perth, The Ghan to Alice Springs and Darwin, The Overland to Melbourne and the seasonal Great Southern to Brisbane.

The Pichi Richi Railway is considerably more distant from Adelaide, based at Quorn, and runs services through to Port Augusta.

[12] Steam trains ceased on 2 April 1929 and the line was closed to be rebuilt as a double track standard gauge, electrified at 600 V DC and converted to tramway operation.

Despite the earlier geographic expansion, by 1920 the infrastructure and rolling stock of South Australian Railways (SAR) had become run down, inadequate and outdated.

During his reign, track, bridges, railway workshops, rolling stock and especially steam locomotives were all modernised and upgraded along essentially American lines.

Following the conclusion of the war, the industrial activity in Athol Park was maintained for a period, before declining to an extent that the Finsbury line was regarded as unnecessary, leading to its removal.

A more limited peak-hour passenger service to Penfield continued after the war, serving staff at the government Weapons Research Establishment, later to become the Defence Science and Technology Organisation (DSTO).

The Commonwealth Railways (CR), owned by the Federal Government, also had a significant role in the northern part of SA, with lines from Port Augusta across the Nullarbor Plain to Kalgoorlie, and to Marree and Alice Springs.

During the early 1970s, the Whitlam Federal Government proposed a strategy to nationalise and standardise the various state rail systems around Australia.

The result was that in March 1978 the SAR became defunct and South Australia's railways were split between Commonwealth and State Government ownership.

A new Commonwealth Government organisation, Australian National Railways Commission (ANR), took over all the former SAR and CR track in South Australia outside the metropolitan area.

In 1994, the STA was abolished and reformed as the government-owned corporate body TransAdelaide as a prelude to competitive tendering for operation of bus and rail services in metropolitan Adelaide.

[31][32] However, in June 2019 when some museum track had already been dismantled, the development was "put on hold" while a North West Planning Study was conducted; a forecast cost increase to $40 million was cited.

A short platform face was also constructed for Railway Museum heritage services running along a parallel stretch of track.

[38][39] In 2019, Renewal SA delivered a Draft Structure Plan of a 94 hectare area of land in Aldinga which is set to include a new school and a railway station as an extension of the Seaford line.

[41] The SA government has allocated $10 million to explore extending Adelaide's rail line further north and south of the city including an extension of services from Belair to Mount Barker.