Paris: Métro
The Paris Métro is a symbol of the city and it's known for its density within the city limits, uniform architecture and unique entrances influenced by Art Nouveau. It is mostly underground and 214 kilometres (133 mi) long. It has 302 stations, of which 62 have transfers between lines. There are 16 lines (with an additional four under construction), numbered 1 to 14 with two lines, 3bis and 7bis, which are named because they started out as branches of Line 3 and Line 7; later they officially became separate lines. Lines are identified on maps by number and colour, with the direction of travel indicated by the terminus. It is the second busiest metro system in Europe, after the Moscow Metro, as well as the tenth busiest in the world. It carried 1.520 billion passengers in 2015, 4.16 million passengers a day, which amounts to 20% of the overall traffic in Paris. It is one of the densest metro systems in the world, with 245 stations within the 86.9 km2 (34 sq mi) of the City of Paris. Châtelet–Les Halles, with five Métro lines, three RER commuter rail and platforms up to 800 metres apart, is one of the world's largest metro stations. However, the system has generally poor accessibility, because most stations were built well before this became a consideration. The first line opened without ceremony on 19 July 1900, during the World's Fair (Exposition Universelle). The system expanded quickly until the First World War and the core was complete by the 1920s. Extensions into suburbs and Line 11 were built in the 1930s. The network reached saturation after World War II with new trains to allow higher traffic, but further improvements have been limited by the design of the network and in particular the short distances between stations. Besides the Métro, central Paris and its urban area are served by the RER, developed beginning in the 1960s, several tramway lines, Transilien suburban trains and two VAL lines, serving Charles de Gaulle Airport and Orly Airport. In the late 1990s, the automated Line 14 was built to relieve RER A. A large expansion of the network is currently under construction - Grand Paris Express - new orbital Metro lines around the Île-de-France region, outside Paris city limits.