It is part of the 'Future Development of Railway Infrastructure' plan (German: Zukünftige Entwicklung der Bahninfrastruktur or 'ZEB') and increases capacity on the Aarau–Olten line in the Schönenwerd–Däniken section.

[1][2][3] A particularly constraining bottleneck in the Swiss rail infrastructure is in the section between Aarau and Olten,[4][5] which has only two tracks at Eppenberg-Wöschnau, Schönenwerd and Gretzenbach.

The Federal Assembly adopted the law authoring the 'ZEB' programme in the spring session of 2009, authorising the budget for the Eppenberg tunnel.

[6][7] Due to the large financial requirements for the New Railway Link through the Alps project, construction of the Eppenberg tunnel only began in 2015.

This included clearing, earth moving, slope protection, demolition work, road construction and other measures.

On 2 May 2015, a tunnel construction party with the official groundbreaking took place at the construction site near Wöschnau, in which Federal Counsellor Doris Leuthard, the SBB Group Management, the Government Council of the Canton of Aargau and the Government of the Canton of Solothurn participated.