The lines involved provide significant orbital passenger services and important freight routes, as well as other movements.
During autumn 2008, works requiring extended closure were conducted on extensive parts of the London Overground network, mainly to allow the passage of freight trains to W10 gauge.
For example, the bridge over Shoreditch High Street that links the realigned route to Whitechapel with the Haggerston viaduct has been installed.
The extended line between Dalston Junction in the north and Crystal Palace and West Croydon in the south is due to open as part of London Overground in 2010.
However, lengthening of trains to four units, along with increase in service to 4tph over the whole network, appears to have been pushed into the medium term, planned for 2011.