The SBB (Swiss Federal Railways) awarded the main contract section for the four-track upgrading of the Olten–Aarau route in November 2014. The contract worth some 274 million Swiss francs was awarded to the Marti Eppenberg JV. It involves the roughwork for the Eppenberg Tunnel as well as its accesses in the Wöschnau and in Gretzenbach. The SBB embarked on the preliminary work for the tunnel and its access sections in early September 2014. The main operations are scheduled to start in spring 2015 and will last until late 2020. The upgrade to create a four-track route is being accomplished within the scope of the ZEB major rail infrastructure project.
The JV headed by the Marti Tunnelbau AG will excavate the two-track, 3 km long tunnel with a tunnel boring machine. This emerged as the most economic approach. In addition a TBM drive results in fewer emissions for local residents and the environment than by tackling the scheme conventionally via drill+blast. The bids for furnishing the tunnel and the access sections with rail technology (tracks, overhead wire, signals etc.) will be undertaken separately, probably in summer 2017.
Thanks to upgrading the Olten–Aarau line (Eppenberg Tunnel) to produce four tracks the state and the SBB intend removing the Olten–Aarau bottleneck by the end of 2020. By and large the project embraces developing the Olten access, a fourth, 2.6 km long track between Dulliken and Däniken and as the core, the twin-track, 3 km long Eppenberg Tunnel as well as extensive connecting measures. There will also be new tracks laid at Olten Station as part of the scheme. The overall project will cost 855 million Swiss francs.