Airports of London cannot be expanded due to the docks on either side. It is also the only airport serving London which does not operate at night. A light rail service from London City Airport DLR station, which adjoins the terminal building of London City Airport, links it to the financial district of the City of London at Bank and Monument stations, which offer interchanges with London Underground. Located in the London Borough of Hillingdon, Heathrow is by far the largest of London's airports and considered the main gateway into the United Kingdom for non-European visitors. Heathrow has four terminals and two parallel
History of the London Underground line, took over part of the Bakerloo line; it was extended through the Docklands to Stratford in 1999. Under the control of the Greater London Council, London Transport introduced in 1981 a system of fare zones for buses and underground trains that cut the average fare. Fares increased following a legal challenge but the fare zones were retained, and in the mid-1980s the Travelcard and the Capitalcard were introduced. In the early years of the 21st century, London Underground was reorganised in a public–private partnership where private companies upgraded and maintained the infrastructure. In 2003 control passed to Transport for