Construction work began on September 20 on the 9·6 km link between Oerlikon and Altstetten that will see a further set of through platforms created beneath Zürich's increasingly-congested central station

EXPECTED to open to S-Bahn traffic in 2013 and inter-city trains from 2015 at a cost of SFr1·82bn, the Durchmesserlinie project is intended to relieve the pressure on Zürich's Hauptbahnhof, provide for an expansion of the S-Bahn network and reduce journey times from eastern Switzerland.

At present, most trains crossing Zürich from east to west, including many long-distance services as well as several S-Bahn routes, must reverse at Hauptbahnhof, a station that Swiss Federal Railways admits has reached its capacity limit.

Some of the pressure on the terminus has been relieved by the opening of four platforms at Sihlpost, adjacent to Hauptbahnhof and connected to it by moving walkway, to handle S-Bahn traffic from Wipkingen and the western shore of Lake Zürich. However, SBB sees this only as a 'stop-gap' facility pending the opening of new deep-level through platforms at Löwenstrasse.

Löwenstrasse will have two island platforms, 430 m long and 13 m wide. This is around 3 m wider than the platforms at Museumstrasse, the low-level S-Bahn station which lies under the northern side of Hauptbahnhof. Located at a depth of 16 m below platforms 4 to 9 of the main station, Löwenstrasse will also be deeper than its neighbour.

Around 10 exits to the levels above will be provided, and, in keeping with its future role as an inter-city station, SBB has committed to building a brighter and more spacious facility than Museumstrasse, with as much natural light as possible filtering down to the platforms.

Cut and cover

The current Sihlquai subway underneath Hauptbahnhof is being widened so that passengers will be able to reach the city centre or catch onward connections more easily. Thanks to SFr57m in advance funding from the canton of Zürich, widening of the Sihlquai subway to facilitate disabled access is already underway and is expected to be finished in 2008. An additional pedestrian subway, the Passage Gessnerallee, will connect Löwenstrasse with Museumstrasse and the main station concourse.

The station itself will be built as a cut-and-cover box. Platforms 3 and 4 at Hauptbahnhof were shortened by 100 m last month to permit a shaft to be sunk down to the sub-surface site, from where the station box will be excavated. As work progresses underground, small sections of platforms 5-18 will be closed progressively, but no major blockade of the terminal platforms is envisaged.

Engineers face an additional challenge from the River Sihl, which flows broadly parallel to the longitudinal pedestrian subways under the terminus. The Sihl is to be temporarily drained to permit construction of another concrete box, which will sit on top of that for the Löwenstrasse platforms, leaving the river to run beneath Hauptbahnhof and resume its natural course.

Weinberg tunnel

At the heart of the new line will be the 4·8 km Weinberg tunnel connecting Löwenstrasse with Oerlikon in the north of the city. Another sensitive engineering project, the S-shaped double-track tunnel must be bored underneath the historic southern wing of the main station before crossing under the River Limmat. Four emergency escape galleries will be provided.

At Oerlikon, where the existing lines from Hauptbahnhof and Altstetten also emerge from tunnels, the present cutting will be widened from four to six tracks, requiring two road bridges to be rebuilt.

Construction of the tunnel and the junction at Oerlikon is expected to take six years and cost around SFr645m.

West to Altstetten

Trains running from Oerlikon will pass through Löwenstrasse before emerging from the tunnel and climbing to a junction at Langstrasse. From there, S-Bahn services will be able to join the existing line curving south and east towards Wiedikon, whilst other S-Bahn and inter-city services continue westwards towards Altstetten.

S-Bahn trains via Wiedikon are forecast to begin using the Weinberg tunnel and low-level platforms from 2013, but the connection to Altstetten will not open until 2015. Two flyovers are to be constructed at a cost of SFr283m to carry westbound trains over a series of junctions and sidings, avoiding conflicting movements on the busy approaches to Hauptbahnhof.

A 394 m flyover at Kohlendreieck will run from Langstrasse to Hardbrücke, and the S-shaped Letzigrabenbrücke, 1156 m in length, leads directly into Altstetten station. Both will rise up to 16 m above ground, and will be fitted with sound baffles to limit noise from passing trains.

Funding for the Durchmesserlinie project is coming jointly from SBB and the canton of Zürich, with the federal railway contributing around 60% of the projected total. SBB predicts that travellers on the Genève – St Gallen corridor are set to be the greatest beneficiaries of the new line, with journey time reductions of up to 30 min envisaged for some inter-city trains (RG 10.07 p591).

  • CAPTION: The sub-surface Durchmesserlinie will help relieve some of the pressure on the congested approaches to Zürich Hauptbahnhof