The SBB are expanding the connections between Zurich and central Switzerland. The centerpiece is the completion of the Zimmerberg base tunnel with a total length of almost twenty kilometers.
Work began as early as 2000 on the first stage of the Zimmerberg Base Tunnel, the double track from Zurich to Thalwil.
In the case of a so-called project of the century, the realization usually takes a very, very long time and the costs are enormous. In the case of the Zimmerberg Base Tunnel, one can confidently speak of a project of the century: It will probably not be completed until 2037, and the costs that will still be incurred are already estimated at 1.4 billion Swiss francs.
Scenic, but . . .
Actually, the Zimmerberg Base Tunnel is almost halfway done. In 2003, the first section was opened as a double-track tunnel from Zurich to Thalwil. At some point, however, there was no money for the underground continuation to Baar. The project was postponed, the second section is only now being redesigned. After all, the first decisions on the route and the type of tunnel construction are now known. The SBB informed about this on Wednesday.
For SBB, there is no question that a better connection is needed between Zurich, Zug and Lucerne, but also between Zurich and Ticino. Their forecasts predict that total traffic in Switzerland will grow by around a third by 2050. On the Zurich-Zug-Lucerne axis, however, demand will grow much more strongly in the same period – by an estimated 50 percent.
Today’s route is scenically very pretty – with views of Lake Zurich and the Glarner Alps as well as a brief view of the Sihl and Sihltal. However, there are two bottlenecks that make it impossible to expand the rail service. One is the single-lane Albis Tunnel near Sihlbrugg, the other is the Thalwil junction. Without the Zimmerberg Base Tunnel 2, the additional passenger numbers could not be managed at all.
Slightly longer than the Vereina Tunnel
The Zimmerberg Base Tunnel 2 connects to the existing tunnel in the Nidelbad area. The siding for this was already created during the construction of the double track between Zurich and Thalwil. The second stage of the Zimmerberg Tunnel will be 10.8 kilometers long. Together with the first section, this results in a total length of 19.2 kilometers – making the Zimmerberg tunnel the fourth longest railway tunnel in Switzerland after the Gotthard, Lötschberg and Simplon, but ahead of the Vereina.
The construction of the Zimmerberg Base Tunnel 2 will enable a significant improvement in services. A Regio-Express that runs every 15 minutes is to connect Zurich with Baar, Zug and Rotkreuz. The Interregio from Zurich to Lucerne will continue to run every half hour, but without stopping in Baar or Rotkreuz. In the direction of Ticino, a continuous half-hourly service will also be created.
The travel time from Zurich to Baar will be reduced by six to eight minutes, so it will only be a good quarter of an hour. As with the construction of the Zurich S-Bahn, this could also have an impact on settlement development in the Baar and Zug areas. Such travel times are of course attractive enough to commute from there to Zurich. There are some districts within the city of Zurich from which it takes longer to get to the city center.
The SBB have examined four variants for the Zimmerberg base tunnel – with shorter or longer routes, with a double-track tunnel or with two single-track tunnels. Ultimately, the decision was made to use the most direct connection and two single-track tunnels. With these, the maximum permissible speed drops from 200 to 160 km/h, but the construction is surprisingly cheaper.
Use excavation on site
Because of new regulations, the double lane also requires an emergency tunnel, which must be passable by buses. With two single-track tunnels, all you need is a so-called cross passage every 500 meters, i.e. a connection between the two tunnel tubes; the construction of the additional rescue tunnel is not necessary. The rescue tunnel was not yet mandatory for the Zurich–Thalwil double track. There are only three emergency exits.
With the 2035 railway expansion step, the federal government is investing almost 13 billion francs in projects throughout Switzerland. The cost of the Zimmerberg Base Tunnel 2 is currently estimated at 1.4 billion – with an accuracy of plus or minus 30 percent. If everything goes according to plan, the plans for the tunnel will be published in 2026, construction is scheduled to begin in 2029 and the structure is scheduled to go into operation at the end of 2037.
SBB planning work is currently concentrating on the Litti area north of Baar. The portal of the Albis tunnel of the existing railway line is located there, and from there the two single-track tunnels for the Zimmerberg tunnel are to be advanced. In the interests of sustainability (and also lower costs), the SBB do not want to remove the excavation, but rather redesign the area around the portals with it.
The SBB are working together with the specialist departments of the canton of Zug and have already informed the residents, who should ultimately benefit from the measure – among other things, a section of the local motorway is to be covered with the tunnel excavation.