Paris for 31 percent of the GDP of France. According to the Economist Intelligence Unit Worldwide Cost of Living Survey in 2018, Paris was the second-most expensive city in the world, behind Singapore and ahead of Zurich, Hong Kong, Oslo and Geneva. The city is a major rail, highway, and air-transport hub served by two international airports: Paris-Charles de Gaulle (the second busiest airport in Europe after London Heathrow Airport with 69.5 million passengers in 2017) and Paris-Orly. Opened in 1900, the city's subway system, the Paris Métro, serves 5.23 million passengers daily, and is the second busiest metro system in
Paris suburbs of Paris, opened to commercial traffic in 1974 and became the busiest Parisian airport in 1993. For the year 2017 it was the 5th busiest airport in the world by international traffic and it is the hub for the nation's flag carrier Air France. Beauvais-Tillé Airport, located north of Paris's city centre, is used by charter airlines and low-cost carriers such as Ryanair. Domestically, air travel between Paris and some of France's largest cities such as Lyon, Marseille, or Strasbourg has been in a large measure replaced by high-speed rail due to the opening of several high-speed TGV rail