Economy of London project is construction of 42 km (26 mi) of new tunnels connecting stations in central London including a branch to Canary Wharf in east London. It is Europe's biggest construction project with a £15 billion projected cost. An additional line, Crossrail 2, has been proposed. London is served by six international airports which are the world's busiest city airport system by passenger traffic. These are Heathrow, Gatwick, Stansted, Luton, London City, and Southend. There are a number of proposals for expanding airport capacity for London including expansion of London Heathrow Airport and expansion of Gatwick Airport. The principal argument in
London City Airport Chambéry) has increased in recent years. London City is at its busiest during the winter months, when a number of airlines, most notably British Airways, Swiss and CityJet, fly to ski resort gateway destinations. Zürich, Geneva and Milan are among the destinations popular among winter sports enthusiasts. Due to the airport's proximity to Central London, it has stringent rules imposed to limit the noise impact from aircraft operations. This, together with the physical dimensions of the long runway and the steep glideslope, limits the aircraft types that can use London City Airport. Mid-range airliners seen at London City include the