Airports of London Heathrow, more than Paris and Frankfurt combined, and Heathrow is the European terminus for 11 of the 25 busiest north Atlantic routes. The busiest long-haul route in the world is between London (Heathrow and Gatwick) and New York (JFK and Newark), with a total of 3,898,460 passengers travelling between the two cities in 2011. Airports of London The metropolitan area of London, England, United Kingdom is served by six international airports and several smaller airports. Together, they make the busiest airport system in the world by passenger numbers and the second-busiest by aircraft movements. In 2016, the six airports handled
Circle line (London Underground) with the other London Underground sub-surface lines: the Hammersmith & City line from Hammersmith to just before Aldgate; the Metropolitan line from Baker Street to Aldgate; and the District line from Tower Hill station to Edgware Road station. The line is electrified with a four-rail DC system: a central conductor rail is energised at and a rail outside the running rail at , giving a potential difference of . The running rails are not electrified. Much of the double track railway from the Hammersmith terminus to Westbourne Park station is on a high brick viaduct. East of Westbourne Park the