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
London a major international air transport hub with the busiest city airspace in the world. Eight airports use the word "London" in their name, but most traffic passes through six of these. Additionally, various other airports also serve London, catering primarily to general aviation flights. The London Underground, commonly referred to as the Tube, is the oldest and third longest metro system in the world. The system serves 270 stations and was formed from several private companies, including the world's first underground electric line, the City and South London Railway. It dates from 1863. Over four million journeys are made every