London, the capital of the United Kingdom, has approx. 10 million inhabitants in the urban area. The rail network is accordingly gigantic, its backbone is the more than 400 kilometres long famous London Underground. It is usually overcrowded in the centre during the peak times. Two of the many unusual features are the usage of two live rails (one lateral, one centric) to avoid stray-current corrosion and that the lines don't bear any numbers but names (District Line, Metropolitan Line, Piccadilly Line etc.).
The Underground is supplemented by numerous suburban railways of different operators and the "Overground". Since 2000 there is also a 28 kilometres long tramway network in the southeast suburbs with operational hub in Croydon. Another self-sufficient rail system is the DLR (Docklands Light Railway) which serves some eastern districts of London and is operated fully automatically.
The whole transport system is coordinated by → TfL (Transport for London)
, a holding organization, wich operates the different means of transport partly by own subsidiaries and partly by private franchisees.