Declared a public utility project on January 31, 2013, the RER E extension project aims to strengthen connections between eastern and western Île-de-France, offering a new quality of service.

The Eole project involves extending the current RER E line 55 km westward, from Haussmann Saint-Lazare station to Mantes-la-Jolie station, passing through the La Défense business district and Nanterre. Forty-seven kilometers of existing track between Mantes-la-Jolie (Line J Paris-Mantes via Poissy) and Nanterre will be redeveloped and modernized. An 8-km tunnel will be dug between La Défense and Haussmann Saint-Lazare, the current terminus of the RER E.

The project includes the creation of three stations (Porte Maillot, La Défense Grande Arche, and Nanterre La Folie) and will cross three departments (Paris, Hauts-de-Seine, and Yvelines). In total, more than 650,000 passengers per day will benefit from this new line once it is fully operational.

Located in the heart of the La Défense business district, the future La Défense Grande Arche station will contribute significantly to the development of the business district: a new-generation line, more trains, and a new station whose impressive size will enable it to accommodate large numbers of passengers. It will be the most interconnected line in the Paris region, particularly at La Défense, with connections to Transilien lines L and U, RER line A, tram line T2, metro line 1, and the future Grand Paris Express line 15. A more direct and better-connected link to airports...

The future Eole station will be located under the CNIT, more than 30 meters underground, and connections and transfers to the neighborhood and other transportation lines will be facilitated. It will be accessible via three independent entrances: near the Grande Arche and Avenue Gambetta, in Courbevoie (next to the Mazars tower), Place Carpeaux, on the forecourt, and interconnections with other transportation systems.

Access to the central platform of the RER E will be from a mezzanine overlooking the platform, via various fixed staircases, escalators, and elevators that will be installed there. This level will serve as a transfer hall where the main access points and connections will converge: RER A, tramway T2, Transilien lines L & U, exits to the outside and to Westfield CNIT.

The new station on the La Défense Grande Arche RER line will open in April 2024, connecting eastern Paris with the future Nanterre-la-Folie station in the west. It will subsequently be extended westward to Mantes-la-Jolie.

The challenge for this project was to build an 18,000 m² underground station 32 meters below ground level and to create fast and seamless connections to other transport lines in France's busiest multimodal station (connection to other transport lines) as well as direct access to the La Défense forecourt. The project will involve the redevelopment of Westfield CNIT.

One of the challenges is the ability to deploy solutions that minimize noise pollution and noise propagation to the upper floors. This is why an “acoustic sarcophagus” (floor, walls, and ceiling) envelops the construction site under Westfield CNIT. The construction site is being carried out through several operations of exceptional technical complexity:

• the temporary shoring of the CNIT has been completed
• the underpinning of 120 columns
• the excavation of the site
• the construction of the main station building, approximately 25 m high and over 200 m long
• the creation of transfer areas with public transport and the CNIT
• the creation of various exits for the RER E, while ensuring that the station is accessible to people with reduced mobility (elevators, platforms, ramps, anti-slip devices, and warning strips).

• A new RER line to serve La Défense from east to west.
• Two exits providing access to the various neighborhoods around the CNIT, two connections to other transport services, and direct access to the CNIT.
• More trains that are faster, more comfortable, and more modern.
• A new station designed to accommodate large numbers of passengers and facilitate connections by providing new transit areas
• A station and trains accessible to people with reduced mobility (elevators, escalators, trains at platform level, etc.)

• Time savings on your journey: for example, from Mantes-la-Jolie to La Défense in 40 minutes instead of 52 minutes, and from La Défense to Magenta in 10 minutes instead of 19 minutes today
• Better connectivity within the Île-de-France network: more connections in Paris, including connections with RER lines B and D at Magenta, and easier access to airports
• An RER that contributes to the improvement of other transport services: decongestion of the RER A, B, and D lines and Saint-Lazare station
• An interconnected station: RER A, metro line 1, Transilien L & U, T2, and the future Grand Paris line 15

• 2016: Preparatory work for the tunnel to La Défense: diversion of networks, preparation for groundwater lowering, preparation of the tunnel excavation shaft.
• 2017: Preparatory work, implementation of groundwater lowering, installation of the construction site, particularly under the CNIT, and modification of the CNIT foundations using the underpinning technique.
• 2018–2021: Creation of new foundations for the CNIT to support the main structure of the station, excavation and civil engineering work for the station, and tunneling on either side of the station.
• Mid-2021–mid-2023: Finishing work on the station and railway infrastructure equipment.
• 2023 to 2024: testing and trial period
• April 2024: commissioning, with trains initially running only during off-peak hours between Haussmann, Porte-Maillot, La Défense, and Nanterre, before “normal” service begins the following fall.

The station floor will be located 40 meters underground. In total, more than 140,000 m3 of earth has been excavated. Ultimately, it is as if the Montparnasse Tower had been laid down beneath the Westfield CNIT.