In addition to London's radial lines and cross-London routes, there are also several orbital National Rail lines connecting peripheral inner-London suburbs.
These lines have been under the management of TfL since November 2007 and are operated by private contract under the London Overground brand.
This commuter transport is operated as a rapid transit system with high-frequency services around a circular route with radial branch lines and is designed to reduce stress from the inner-city Tube network by allowing commuters to travel across London without going through the central Zone 1.

London Overground was formed by joining a series of existing railway lines to form a circular route around the city and incorporates the oldest part of the Underground's history, the Thames Tunnel under the River Thames, which was completed in 1843.
The routes comprise:
The North London Line, which arcs across North London from Richmond in the west via Willesden Junction and Highbury & Islington to Stratford in the east.

The West London Line linking Clapham Junction to Willesden Junction with some trains to Stratford via the North London Line.

The East London Line (including the South London Line), a former London Underground line which was converted to heavy rail operation in 2010; part of the Brighton Main Line between New Cross Gate and Norwood Junction; and the South London Line which was added to the London Overground network in December 2012, completing the circuit across the South London suburbs to Clapham Junction.
Running from Highbury & Islington to New Cross, West Croydon, and Crystal Palace, and via the South London Line, Clapham Junction.

Other routes operated include:
The Gospel Oak to Barking Line which links inner North London to the northeastern suburbs, which is due to be extended to Barking Riverside.

The inner-suburban Watford DC Line from Euston to Watford Junction.

Suburban services from Liverpool Street to Chingford, Enfield Town and Cheshunt via Hackney Downs.

The Romford to Upminster Line via Emerson Park.
In addition to London's radial lines and cross-London routes, there are also several orbital National Rail lines connecting peripheral inner-London suburbs. These lines have been under the management of TfL since November 2007 and are operated by private contract under the London Overground brand. This commuter transport is operated as a rapid transit system with high-frequency services around a circular route with radial branch lines and is designed to reduce stress from the inner-city Tube network by allowing commuters to travel across London without going through the central Zone 1.
London Overground was formed by joining a series of existing railway lines to form a circular route around the city and incorporates the oldest part of the Underground's history, the Thames Tunnel under the River Thames, which was completed in 1843. The routes comprise:
The North London Line, which arcs across North London from Richmond in the west via Willesden Junction and Highbury & Islington to Stratford in the east.
The West London Line linking Clapham Junction to Willesden Junction with some trains to Stratford via the North London Line.
The East London Line (including the South London Line), a former London Underground line which was converted to heavy rail operation in 2010; part of the Brighton Main Line between New Cross Gate and Norwood Junction; and the South London Line which was added to the London Overground network in December 2012, completing the circuit across the South London suburbs to Clapham Junction. Running from Highbury & Islington to New Cross, West Croydon, and Crystal Palace, and via the South London Line, Clapham Junction.
Other routes operated include:
The Gospel Oak to Barking Line which links inner North London to the northeastern suburbs, which is due to be extended to Barking Riverside.
The inner-suburban Watford DC Line from Euston to Watford Junction.
Suburban services from Liverpool Street to Chingford, Enfield Town and Cheshunt via Hackney Downs.
The Romford to Upminster Line via Emerson Park.
Transport in London