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 changed from serving a closed loop around the centre of London on the north side of the River Thames to a spiral serving Hammersmith. On the Jubilee line a seventh car was added to all trains, in 2006 and a new signalling system allowing automatic operation was commissioned in 2011. On the Victoria line, new trains were introduced between July 2009 and June 2011, and a new signalling system has allowed 33 trains per hour from January 2013. The sub-surface (Metropolitan, District, Circle and Hammersmith & City) lines have been upgraded, with new air-conditioned S Stock. Also, the sub-surface track,