The 4-track main line from Victoria to East Croydon via Balham and Norbury is one of the county's busiest, feeding trains into a complex network of suburban lines, as well as the Brighton Main Line and routes to other Sussex and South Coast destinations. Almost all services are worked by Southern EMUs.
The line was electrified at 6.6kV AC using overhead equipment, prior to the grouping in 1923, then converted to 750V DC third rail in the late 1920s. All regular passenger services are operated by EMUs and what freight traffic there is mostly runs at night.