Mandurah line

The Mandurah line, also known as the Southern Suburbs Railway, is a suburban railway line and service in Western Australia, linking Perth's central business district (CBD) with Mandurah to the south. Operated by the Public Transport Authority (PTA) as part of the Transperth system, the Mandurah line is 70.8 kilometres (44.0 mi) long and has thirteen stations. It commences as a through service with the Yanchep line in the William Street tunnel under the CBD, where two stations are. South from there, the line enters the median strip of the Kwinana Freeway, where five of the line's stations are. The line diverges from the freeway for the southernmost six stations in the cities of Kwinana, Rockingham and Mandurah.

Planning for the Mandurah line commenced during the construction of the Yanchep line in the early 1990s. By the late 1990s, the plan was for the Mandurah line to branch off the Armadale line at Beckenham and follow the Kwinana freight railway to reach the Kwinana Freeway. After the election of a Labor government at the 2001 state election, the planned route was changed to go via a tunnel under the CBD instead. Commencing in February 2004, the Mandurah line's construction was divided into seven major contract packages. The construction of the William Street tunnel was particularly difficult due to labour strikes and contract disputes.

The Mandurah line was designed similarly to the Yanchep line, using widely-spaced stations with bus interchanges and large park-and-rides. Originally planned to open between Perth and Warnbro station in 2006 and between Warnbro and Mandurah in 2007, the William Street tunnel opened on 15 October 2007 and the rest of the line opened on 23 December 2007. Two infill stations have opened since: Aubin Grove on 23 April 2017 and Lakelands on 11 June 2023; two more have been proposed: South Perth and Karnup. In June 2025, the Thornlie–Cockburn Link is planned to open, connecting the Thornlie line to the Mandurah line at Cockburn Central station via the route originally proposed for the Mandurah line.

B-series and C-series trains are the main rolling stock used on the Mandurah line, with A-series trains formerly commonly used as well. Trains run at a fifteen minute headway, reducing to as low as a five minute headway in peak, with some services terminating at Cockburn Central during peak. The travel time from Perth to Mandurah is 54 minutes. The line has exceeded patronage expectations, reaching a peak of 21,874,779 boardings in the 2023–24 financial year, making it the busiest line in the Transperth system.