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The Ile-de-France Mobilités network has five RER lines crisscrossing the region.

The RER lines (Réseau Express Régional or Regional Express Network) are different from other train lines because they do not terminate in Paris. They cross the capital underground, so that passengers can get from one side of the region to the other on the same line. These five lines alone carry more than three million passengers. They are either jointly operated by RATP and SNCF (Lines A and B) or operated by SNCF alone (Lines C, D and E).

A short history of the RER

The first RER line, created in the 1970s, is the current RER A. Crossing Ile-de-France from west to east over 109 kilometres (including 26 kilometres underground), it is today the most used rail line in Europe with regular peaks of more than 1.3 million passengers per day. At rush hour 640,000 passengers use it, more than the population of the city of Lyon. The second busiest line in Europe is also an RER line, Line B running from north to south, which regularly exceeds one million passengers per day.

The increase in ridership

RER lines have to cope with very strong growth in passenger numbers, a 20% increase over the last ten years. This has led to a poorer service on many sections. To deal with this problem, Ile-de-France Mobilités has launched numerous investment programmes, together with the operators (RATP, SNCF), network services (SNCF Réseau), national government, the Ile-de-France Region and local authorities, and in permanent consultation with elected officials and passenger associations. The objective is to offer residents of the Paris region a high quality of service.