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
Liège Airport "golden triangle" Paris - Amsterdam - Frankfurt that handles 66% of European freight, and 75% when taken together with London. In 2014 it was the eighth-biggest cargo airport in Europe. Liège Airport is the biggest cargo airport in Belgium, and the third-biggest for passengers after Brussels Airport and Brussels South Charleroi Airport. It is the global hub of ASL Airlines Belgium (the former "TNT Airways"), the European hub of Allied Air, Astral Aviation, CAL Cargo Air Lines, El Al Cargo, Ethiopian Cargo, and Icelandair Cargo, and a key European cargo hub for ABX Air, AirBridge Cargo, Bluebird Cargo, Emirates, i-Fly