The Thornlie 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 Thornlie line is a branch of the Armadale line and runs for parallel to the Kwinana freight railway between the Armadale line at Kenwick and Thornlie station. Thornlie line services continue north of Kenwick along the Armadale line to Perth station, stopping at most stations, in contrast to Armadale line services, which skip most stations along that section.
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 planned Mandurah line route changed in 2001, but not before tunnels were built for the line to exit the Armadale line at Kenwick and enter the Kwinana Freeway. It was decided to built 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.
Since 2017, there have been plans to extend the Thornlie line to Cockburn Central station on the Mandurah line, known as the Thornlie–Cockburn Link. This project is being built as part of Metronet and involves the construction of two new stations along the way. The main construction contract was awarded to a joint venture between CPB Contractors and Downer in December 2019 at a cost of $716 million. Construction started in 2020 and the extension was expected to be open in 2023. The cost has since increased to $1.124 billion and the project is now planned to be complete by mid-2025.
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 in Beckenham, 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 Beckenham tunnel was built and Albany Highway was grade separated from the freight railway. The long 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 the 2001 state election, 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 though as a one station branch of the Armadale line to Spencer Road using the Beckenham tunnel. 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.