The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England. It is the oldest underground railway in the world, the first section of which opened in 1863. In 1890 it became the first to operate electric trains. The whole network is commonly referred to by Londoners and in official publicity as the Tube. The Underground serves 270 stations and has 402 kilometres of track, making it the second largest metro system in the world in terms of route miles, after the Shanghai Metro. In 2007, more than one billion passenger journeys were recorded, making it the third busiest metro system in Europe, after Moscow and Paris. The tube is an international icon for London, with the tube map, considered a design classic, having influenced many other transport maps worldwide.