Réseau Express Régional

The Réseau Express Régional (French pronunciation: ​[ɛʁ.ə.ɛʁ]; English: Regional Express Network), colloquially called the RER, is a hybrid commuter rapid transit system in France serving Paris and its suburbs. The RER combines a modern suburb-city centre underground rail system and commuter rail lines. It has several connections with the Paris Métro within the city of Paris. Also inside the city, the RER functions much like the Métro, but is faster as it has fewer stops. The network consists of five lines: A, B, C, D and E. The lines are identified by letters to avoid confusion with the Métro lines, which are identified by numbers. The RER is still expanding: Line E, which opened in 1999, is planned for westward extension in two phases by 2020–2022.

The RER contains 257 stations, 33 of which are within the city of Paris, and runs over 587 km (365 mi) of track, including 76.5 km (47.5 mi) underground. Each line passes through the city almost exclusively underground and on dedicated tracks. The RER is operated partly by RATP, the transport authority that operates most public transportation in Paris, and partly by SNCF, the national rail operator. In spite of this, the system uses a single fare structure and no transfer is needed between sections run by the two operators. Total traffic on the central sections of lines A and B, operated by RATP, was 452 million people in 2006; in the same year, total traffic on all lines operated by SNCF (both RER and Transilien trains) was 657 million.

RATP manages 65 RER stations, including all stations on Line A east of Nanterre-Préfecture and those on the branch to Saint-Germain-en-Laye. It also operates stations on Line B South of Gare du Nord. Other stations on the two lines and those on lines C, D and E are operated by SNCF. Of the RER stations operated by RATP, 9 have interchanges with Métro lines, and 9 allow transfer to SNCF's Transilien service.

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