Thornlie–Cockburn line

The Thornlie–Cockburn line is a suburban railway line and service in Perth, Western Australia, operated by the Public Transport Authority as part of the Transperth system. The line branches from the Armadale line in Kenwick and heads south-west on a 20.5-kilometre (12.7 mi) route alongside the Kwinana freight railway and the Kwinana Freeway to Cockburn Central. Thornlie–Cockburn line services continue north-west of Beckenham station alongside Armadale line services, terminating at Perth station.

The line opened on 7 August 2005 as the Thornlie line, originally a one-station spur off the Armadale line that ran 2.9 kilometres (1.8 mi) along a single track to Thornlie station. Thornlie line trains served most stations north of Kenwick on the Armadale line to Perth station, complementing Armadale line trains which ran express through much of this section. The Thornlie line was temporarily closed on 20 November 2023 for construction work to remove level crossings and extend the line to Cockburn Central station on the Mandurah line. Renamed the Thornlie–Cockburn line, it reopened on 8 June 2025 with new stations at Nicholson Road and Ranford Road.

The Thornlie–Cockburn line originated from initial plans for the Mandurah line, which was to branch off from the Armadale line along the Kwinana freight railway between Kenwick and Jandakot before heading south. The Mandurah line's planned route changed in 2001, but not before rail tunnels in Kenwick and Jandakot had been built. As part of the new plan, a single-station spur line to Thornlie was announced, which would adapt the nearly-completed Kenwick rail tunnel to serve the area that the Mandurah line would now bypass. The main construction contract was awarded to Barclay Mowlem in 2004 with the line opening the following year.

Plans arose in 2017 to extend the Thornlie line by 14.5 kilometres (9.0 mi) to Cockburn Central station on the Mandurah line, a project known as the Thornlie–Cockburn Link. This project is currently being built as part of Metronet and involves the construction of two new stations. The main construction contract was awarded to a joint venture between CPB Contractors and Downer in December 2019 at a cost of A$716 million. Construction started in 2020 and it was expected to be complete in 2023, though it experienced delays and cost increases to A$1.352 billion. On 20 November 2023, the Thornlie line was temporarily closed to allow for works on both the Victoria Park-Canning Level Crossing Removal and Thornlie–Cockburn Link projects. The Thornlie–Cockburn line reopened on 8 June 2025 under its new name.