New details on the Zimmerberg Tunnel

It will be some time before trains run into the tunnel on the Baar Litti line to Zurich Vorbahnhof. In the meantime, however, further details of the billion-dollar project are leaking out.

Anticipation is said to be the most beautiful type of joy. In the case of Zimmerberg 2 Tunnel major project of the SBB (Swiss Federal Railways), this exhilaration will certainly last until 2037, or at best a little longer. In the meantime, however, there is news.

In the "Swiss Railway Review" magazine (5/2022), SBB general project manager Thomas Schweizer and overall study director Christoph Fessler write of "obvious adjustments". For the railway experts, these include the "shortest possible connection" instead of a "long curve" for the route for the Zimmerberg 2 tunnel (Thalwil Nidelbad – Baar Litti)

As a result of this "optimisation", the new railway tunnel that is to be built will be around 1.8 kilometres shorter, with a length of 10.8 kilometres. The tunnel that is already used between Thalwil and Zurich measures 8.4 kilometres. This means that rail passengers will disappear under the Zimmerberg for a total length of 19.2 kilometres.

The supplemented Zimmerberg Tunnel will thereby achieve a top position: with 19.2 kilometres of rail travel in the mountain, it is the longest SBB tunnel in the lowlands. In the best case, it should result in a travel time shortened by up to eight minutes.

When it opens, the tunnel will be the fourth longest in Switzerland. Only the Gotthard (57.1 kilometres) and the Lötschberg Base Tunnel (34.6 kilometres) and the Simplon tunnel (19.8 kilometres) will be longer than the Zimmerberg.

The travel time between Baar and Zurich is to be reduced from 23 to 16 minutes. From Zug's point of view, it is acceptable that the extension of the second Zimmerberg tunnel would make the purposed Meilibach tunnel longer. This will one day branch off from the Zimmerberg Tunnel and lead to the left bank of Lake Zurich.

Two single-track tubes as the solution
Thomas Schweizer and Christoph Fessler also explain why the Zimmerberg-2 tunnel should be built in two separate tubes. The most important driver for the decision of the now chosen design is that it will cost less than the double-track tube, as an additional safety tunnel would have to be planned for a double-track solution.

According to the report in the "Swiss Railway Review", the main installation site is to be in the Baar Litti area, where the excavated material is to be deposited. The report mentions 2.1 million cubic metres.

There are some advantages from this for the builders: the Zimmerberg, as a promontory of the Albis chain, has a "good-natured geology".

The maximum tunnel speed is given as 160 kilometres per hour
The tunnel will be designed in such a way that trains can run at speeds of up to 160 kilometres an hour. The report also states that it should be possible to have a train running to Zurich at this speed every 15 minutes.

In the course of this expansion, the access road, as well as the existing line will also have to be upgraded. The SBB expects a construction period of eight years, starting in 2029. The cost of all this: CHF 1.2 billion. But that’s only a prognosis.