The Thornlie–Cockburn line, formerly the Thornlie line, is a suburban railway line in Perth, Western Australia, which is operated by the Public Transport Authority as part of the Transperth system. The line branches off the Armadale line south of Beckenham station and runs for to Cockburn Central station on the Mandurah line. North of Beckenham station, Thornlie–Cockburn line services run alongside the Armadale line to Perth station.
The Thornlie line originated from initial plans for the Mandurah line, which was to branch off the Armadale line and run along the Kwinana freight railway. The Mandurah line's planned route changed in 2001, but not before tunnels were built for the line to exit the Armadale line south of Beckenham and enter the Kwinana Freeway. It was decided to build the Thornlie line instead as a one-station branch of the Armadale line. The main construction contract was awarded to Barclay Mowlem in 2004 and the Thornlie line opened on 7 August 2005.
In 2017, planning began on a extension to Cockburn Central station, known as the Thornlie–Cockburn Link. Built as part of the Metronet project, the contract for the Thornlie–Cockburn Link was awarded to CPB Contractors and Downer in December 2019, and construction began in 2020. Originally budgeted at A$716million, the construction cost eventually rose to $1.352billion. On 20 November 2023, the Thornlie line was temporarily closed for construction on the Victoria Park-Canning Level Crossing Removal Project, which resulted in the elevation of five stations between Perth and Beckenham. The Thornlie line reopened on 8 June 2025, upon which the extension opened and the line was renamed the Thornlie–Cockburn line.
Branching from the Armadale line south of Beckenham station, the Thornlie–Cockburn line runs parallel to the Kwinana freight railway, along which there are three stations: Thornlie, Nicholson Road and Ranford Road. At the Kwinana Freeway, the line enters the freeway's median strip and travels parallel to the Mandurah line to terminate at Cockburn Central station. The Thornlie–Cockburn line has a frequency of four trains per hour all day, with lower frequencies at night. The travel time from Perth to Cockburn Central is 36 minutes. All stations on the branch are fully accessible and have platforms; train lengths are limited by several stations between Perth and Calisle with platforms. The line recorded 4,144,783 boardings in the year to June 2026.
History Spur to Thornlie Initial plans for the Mandurah line had the line as a spur off the Armadale line along the Kwinana freight railway in the same manner as the present-day Thornlie line. The South West Metropolitan Railway Master Plan was released in March 1999, detailing the route and stations along the railway. The South West Metropolitan Railway would have diverged from the Armadale line at Kenwick, entering a tunnel to pass under the Perth-bound Armadale line track, Albany Highway, Roe Highway, and the freight railway. It would have then travelled parallel and on the southern side of the freight railway, with stations in Thornlie near Spencer Road, Nicholson Road, and in Canning Vale near Ranford Road, and provisions for a future station at Karel Avenue to serve Jandakot Airport. The railway would have then entered another tunnel at Jandakot, known as the Glen Iris tunnel, to go into the median of the Kwinana Freeway, continuing south from there to Mandurah. Several level crossings on the freight railway were planned to be replaced by road-over-rail bridges, at Albany Highway, Spencer Road, Nicholson Road, and Karel Avenue.
As part of an extension of Roe Highway from Welshpool Road to Kenwick Link and realignment of Albany Highway in the late 1990s and early 2000s, the first stage of the Kenwick tunnel was built and Albany Highway was grade separated from the freight railway. The Glen Iris tunnel was also constructed as part of an extension of the Kwinana Freeway in 2000.
Following the election of the Labor Party in 2001, the Mandurah line was rerouted to follow a more direct route along the Kwinana Freeway to the Perth central business district. It was decided to build the Thornlie line as a one station branch of the Armadale line to Spencer Road using the Kenwick tunnel. Building Nicholson Road station was also considered. A new master plan was released in 2002. Spencer Road was planned to be grade separated and Thornlie station was planned to have a bus interchange and parking for about 450 cars. Patronage for Thornlie station was projected to be 3,500 boardings per day. Patronage was not forecast to be high enough for Nicholson Road station to be built initially, but it was expected to be built in the future. Train frequencies were planned to be four trains per hour upon opening in December 2004.
New MetroRail was formed in 2003 as a division of the Public Transport Authority to manage extensions to railways in Perth, including the Mandurah line, the Thornlie line, and an extension of the Joondalup line to Clarkson station. The second stage contract for the Kenwick tunnel was awarded to John Holland Group in March 2003 at a cost of A$14.225million. The second stage consisted of of tunnel; the realignment of of the Kwinana freight railway, which was leased by Australian Railroad Group at the time; and the construction of noise walls. The total tunnel length after the two stages was . Workers on the John Holland site went on strike in May 2003 to campaign for better pay and conditions. Construction was also disrupted by a solidarity strike in January 2005 in relation to pay conditions for workers on the Mandurah line.
A new traction substation at Beckenham was constructed to power the Thornlie line and provide backup power to the Armadale line, which was mainly powered by a substation at East Perth. The contract for that was awarded to Western Power Corporation in September 2003 at a cost of $3.3million. Other work involved relocating BP's Kewdale White Oil Line, which is a pipeline that carries jet fuel, diesel and petrol from the Kwinana import terminal to Kewdale via the freight railway.
An invitation to tender was sent out on 25 June 2003 for the main contract to build the Thornlie line. This involved constructing Thornlie station, of single track railway, a rail bridge across the Canning River and a road bridge for Spencer Road across the Thornlie line and freight railway. The tender was planned to close on 28 August 2003, but that was extended to 16 December 2003. Barclay Mowlem was announced as the preferred tenderer in February 2004 and was awarded the contract by April 2004. The estimated value of the contract was $30million. By then, the planned opening date was February 2005. Construction had begun by July 2004. Construction was disrupted by strikes. The Construction, Forestry, Mining and Energy Union and union officials were initially fined for breaching an enterprise bargaining agreement, but the fines were overturned by the Federal Court in June 2007. Thornlie station and the Thornlie line were officially opened on 7 August 2005 by Premier Geoff Gallop, Minister for Planning and Infrastructure Alannah MacTiernan, and member for Kenwick Sheila McHale. Full service began on 8 August 2005.
Thornlie–Cockburn Link extension An extension of the Thornlie line to link up with the Mandurah line had been proposed several times in the 2010s. In December 2012, the Labor Party announced it planned to incorporate the Thornlie line into a loop line to link the proposed Airport line to the Fremantle line via the Armadale and Mandurah lines if it were to win the 2013 state election. This was part of its proposed Metronet plan. There would have been stations at Nicholson Road, Ranford Road and a station called South Lake at the intersection with the Mandurah line. The Liberal Party won the election, so that plan did not go ahead. In 2015, RAC WA called for the Thornlie line to be extended to Cockburn Central station on the Mandurah line. The Liberal government's 2016 Transport @ 3.5 million plan called for the extension to be built by the time that Perth reaches a population of 2.7million.
Ahead of the 2017 state election, both major parties committed to extending the Thornlie line to Cockburn Central station. The Liberal government said it could be done at a cost of $520million and be open in late 2023, whereas Labor said it could be constructed for $474million by 2021 as part of its revised Metronet plans. Labor won the 2017 election and planning for the Thornlie–Cockburn Link began in late March 2017. In May, following negotiations between the federal and state governments, it was announced that federal funding for the cancelled Perth Freight Link would be used on the Thornlie–Cockburn Link, subject to assessment by Infrastructure Australia. The September 2017 state budget gave the Thornlie–Cockburn Link a cost of $535.8million.
The business case for the Thornlie–Cockburn Link was submitted to Infrastructure Australia in August 2017. In November 2018, Infrastructure Australia released its assessment of the project, adding the project to the Infrastructure Priority List as a "Priority Project" and giving it a projected economic benefit of $969million and a benefit–cost ratio of 1.2. Other options considered were only extending the Thornlie line to Nicholson Road and having a station there, or only extending the line to Ranford Road and having stations at Ranford Road and Nicholson Road. Extending the line the whole way to Cockburn was found to be the best choice. Infrastructure Australia recommended that the contract for the Thornlie–Cockburn Link be combined with the contract for the Yanchep Rail Extension of the Joondalup line to save costs during procurement, although local contractors expressed concerns that the two projects had different requirements, were in different parts of Perth, and that combining the projects would price out smaller contractors. The Infrastructure Australia assessment allowed $700million in federal funding to be spent on the Thornlie–Cockburn Link and the Yanchep Rail Extension, of which $350million was for the Thornlie–Cockburn Link.
Enabling legislation was introduced to the Parliament of Western Australia in May 2018 and the Railway (METRONET) Act 2018 was passed in November 2018.
Scope The project definition plan, detailing the scope of the project, for the Thornlie–Cockburn Link was approved by state cabinet in July 2018. The project was to involve the construction of two new stations: Nicholson Road and Ranford Road stations, each with two long island platforms, full disabled access, a bus interchange for feeder buses and a park and ride. Nicholson Road station was forecast to have 2,350 boardings per day in 2031 and Ranford Road station was forecast to have 1,985 boardings per day in 2031. of new dual-track railway was to be constructed between Thornlie and Cockburn Central, using the pre-existing Glen Iris tunnel to enter the median of the Kwinana Freeway. Most of this track was to be along the southern side of the freight railway, with the final within the median of the Kwinana Freeway between the two Mandurah line tracks. of single track railway between Beckenham junction and Thornlie station was to be duplicated, including constructing a new bridge across the Canning River. The Kenwick tunnel was already designed for a double tracked railway. To make way for the Thornlie line, of the freight railway was to be relocated slightly north.