Thornlie–Cockburn line

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 17.6 kilometres (10.9 mi) 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 14.5-kilometre (9.0 mi) 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$716 million, the construction cost eventually rose to $1.352 billion. 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 150-metre-long (490 ft) platforms; train lengths are limited by several stations between Perth and Calisle with 100-metre-long (330 ft) platforms.