History of the London Underground to determine the cause. Following the incident, a system that stops a train automatically if the driver fails to brake was introduced at dead-ends on the London Underground. The Northern City Line was connected to British Rail tracks at Finsbury Park in the 1970s. The last tube train ran in October 1975, and British Rail services began in 1976. In 1977, the Piccadilly line was extended from Hounslow to Heathrow Airport, and in 1986 a platform serving Terminal 4 opened on a loop line. The Fleet line through central London was first proposed in 1965, taking over the Bakerloo line's
History of the London Underground 2008. On 7 July 2005 three bombs exploded on underground trains, two on the Circle line at Aldgate and Edgware Road and the third on the Piccadilly line between King's Cross and Russell Square. Later the same day a bomb exploded on a bus in Woburn Place. Four suicide bombers had killed themselves and fifty-two other people, and it took over a month before underground services had been restored. In 2007 the East London line, operated as an isolated shuttle since 1939, closed so that it could be converted into a London Overground line. In December 2009 the Circle line