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
Transport in Paris Thalys line connects Brussels through 1h22 of rail with up to 26 departures/day, Amsterdam in 3h18 with up to 10 departures/day, Cologne in 3h14, with up to 6 departures/day . Paris had its first airport in the fields of Issy-les-Moulineaux (just to the southern limits of Paris by its Seine river's Left Bank) from the first aviation trials of 1908. Aviation became a serious mode of transport during the course of World War I, which in 1915 led to the installation of a larger and more permanent runway installation near the town of Le Bourget to the north of Paris.