RER

The Réseau Express Régional, abbreviated as RER, is a rapid transit network serving the Île-de-France region surrounding Paris. It functions as a hybrid system, combining aspects of a suburban rail network with metro-like service in the city center. Trains travel at higher speeds and over longer distances outside central Paris, while also providing very frequent service through a central tunnel that connects multiple suburban branches.

The network has five lines, designated A, B, C, D, and E. These lines share a common core in central Paris where most trains run through a tunnel, then branch out to distant suburbs and regional towns. The RER integrates with the wider Paris public transport system, including the city’s Métro and the regional Transilien network, enabling transfers at major hubs such as central stations and key interchange points.

The RER was developed from the late 20th century to relieve congestion on the Métro and to improve regional mobility. Over subsequent decades, the system was extended and upgraded, with newer rolling stock and signaling to increase capacity and reliability. It is among the busiest commuter rail networks in Europe, reflecting the high demand for rapid, frequent travel between Paris and its suburbs.

Operations are shared between two public transport entities, with lines run by the RATP and the SNCF according to the route. Rolling stock is electric multiple unit trains designed for rapid acceleration and high passenger capacity, suitable for both long-distance suburban journeys and dense inner-city segments. The RER remains a central component of the Île-de-France transport network and a key corridor for regional economy and daily commuting.

See also: Paris Métro, Transilien, RATP, SNCF, Île-de-France transport.