The SFr 1.6bn ($US 1.6bn) project has been commissioned by Swiss Federal Railways (SBB) as an essential part of its plan to boost services following the introduction of the Leman Express RER in 2019 on the new CEVA line between Cornavin, Eaux-Vives and Annemasse.

The Swiss federal government will contribute just over SFr 1bn to the project, with financing coming from the FABI rail infrastructure fund. The remainder will be covered by the canton of Geneva (SFr 416.6m) and the city of Geneva (SFr 111.3m), subject to approval by the bodies concerned.

The total cost will also cover related projects which have to be completed before work on constructing the extension can begin. These include a new traffic control centre on the line to La Plaine and relocation of train cleaning facilities. According to current plans, preliminary work can begin in 2019, with construction of the station extension itself due to start in 2024.

The extension with two tracks and one platform will be constructed 17m below street level, partly under the existing platform used for trains to France, and partly under the Place de Montbrillant. Access for trains from Lausanne will be via a double-track tunnel, with a single track tunnel from Geneva airport. This underground variant was selected in 2013, the advantage being that it does not involve demolition of residential buildings.

Around 600 trains a day currently pass through Cornavin station. The planned extension is an essential part of the Leman 2030 project to gradually double the numbers of train seats available on the Lake Geneva arc connecting stations in the canton of Vaud, Geneva, and neighbouring areas in France.