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
London Underground S Stock (ex-Metropolitan Railway) London Underground S Stock (ex-Metropolitan Railway) S stock is the designation given to one train of eight cars by London Underground in the 1930s. It was composed of converted trailers and experimental driving motor cars inherited from the Metropolitan Railway in 1933. In 1919, the Metropolitan Railway converted six 1904 saloon stock cars into the "Hustler train". These were the only cars of this type: two were driving motors, two were control trailers, which the Metropolitan called driving trailers, and the remaining two were trailers. In 1936, the two driving motors were converted into trailers, and all six cars were