Suburban Rail Loop

The Suburban Rail Loop (SRL) is a group of new rapid transit lines planned or under construction in Melbourne, Victoria, Australia. The project is divided into four distinct sections. The two main sections, SRL East and SRL North, would together form a single 60 km (37 mi) fully automated orbital metro line through the city's middle suburbs, with 13 stations between Cheltenham and Melbourne Airport connecting to eight existing Melbourne rail lines. SRL East is currently under construction and is planned to open in 2035.

The SRL Airport section, in the city's west, would be formed by the separate Melbourne Airport rail link project, which is being delivered separately by Rail Projects Victoria. This section will run into the central business district via the Metro Tunnel. The final section, SRL West, has not been defined in detail by the state government but would connect the city's outer western suburbs and may be formed by electrifying the existing Deer Park–West Werribee railway line and extending it to Werribee station.

Several orbital rail schemes have been proposed and some constructed throughout Melbourne's history, but the rail network has remained largely radial. The Victorian Labor government led by Premier Daniel Andrews announced the SRL as policy in 2018 in the lead up that year's state election. Initial planning for the SRL was carried out in secret prior to its announcement, and, when the plans were released, it received significant attention. The SRL plan was praised for its long-term vision and ambition, as well as being an innovative solution to the difficulties faced by Melbourne's transport network, but criticised for its political motives and large cost.

SRL East and North would take more than 25 years to construct and together are estimated by the project's business case to cost between $30.7 and $57.6 billion depending on project staging, of which capital costs would be between $24.1 and $45.1 billion. SRL East and North will be built entirely underground along new rail alignments, while SRL Airport will be formed by the at-grade and elevated Melbourne Airport rail link and funded separately.

In 2021, the Victorian government announced that the SRL East, between Cheltenham and Box Hill, would commence construction first and be open by 2035. On 2 June 2022, early works began on SRL East with major construction expected to commence in 2023, followed by tunnelling works in 2026.