The Suburban Rail Loop (SRL) is a rapid transit system currently under construction in Melbourne, the capital of Victoria and second largest city of Australia. The system is divided into four distinct sections. The two main sections, SRL East and SRL North, will eventually 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.The first section, SRL East, is a 26 km (16 mi) underground link from Cheltenham to Box Hill via Monash University and Deakin University. Construction commenced in 2022 with a scheduled opening in 2035. The second section, SRL North, will be a 34 km (21 mi) underground extension of SRL East from Box Hill to Melbourne Airport, via La Trobe University. Construction is not expected to commence until the 2030s, with completion by 2053. This section may be split into two projects due to its length and cost. The third section, SRL Airport, will be formed by the separate Melbourne Airport Rail project. This 15 km (9.3 mi) section will run from Melbourne Airport via Sunshine into the central business district via the Metro Tunnel. Early construction commenced in 2023 before significant funding delays pushed the opening date out to at least 2033. The fourth and final section, SRL West, has not been defined in detail but would connect the city's outer western suburbs and may be formed by electrifying the existing Deer Park-West Werribee railway line from Sunshine and extending it to Werribee. No timeframe for construction has been released.