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 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 component, in the city's west, would be formed by the separate Melbourne Airport rail link project, which began construction in 2022 and is being delivered by Rail Projects Victoria. This component will run into the central business district via the Metro Tunnel, and is planned to open by 2029. 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.
Background
The Melbourne transport network was substantially developed in the late 19th century, when the newly available technology of the railway enabled population growth away from the city centre. The result was the development of a largely radial network, which, over the following century, reinforced a model of urban development focused on heavy daily commuter flows into and out of the CBD. Furthermore, a program of freeway construction in the wake of the 1969 Melbourne Transportation Plan reinforced the structure of the suburbs and introduced car dependence to new regions of development not served by the legacy rail network. As a consequence, Melbourne, unlike many cities of comparable size, did not develop any major centres of employment or dense population in its outlying regions over the course of the 20th century.
A number of orbital lines were constructed at the peak of railway development, but most failed to attract the necessary traffic of passengers and goods to remain sustainable into the late 20th century. The Outer Circle, which ran from Oakleigh on the Dandenong line to Fairfield on the Hurstbridge line via the Glen Waverley and Lilydale lines, was constructed between 1888 and 1891 but closed by 1897, though it was partly reopened as the Alamein branch line. The Inner Circle linking the modern-day Upfield and Mernda lines, was opened in 1888 but closed to passengers in 1941. The Albion-Jacana line and Newport-Sunshine line in the city's west, though performing a similar purpose, were never intended to carry passenger traffic.