AUSZUG | eb - Elektrische Bahnen INT 2/2015

4 113 (2015) INT 2 Focus Citybanan – new railway tunnel for the local traffic in Stockholm Since 2009 a new railway tunnel is being built below Stockholm city centre (Sweden). This should relieve the chronically overloaded two- track line south of the main station Stockholms central and allow an increase in suburban traffic. The commissioning is planned for 2017. The existing line between the stations Stockholms central (Stockholm C) and Stockholms södra is used by commuter trains ( Pendeltåg ), regional trains, inter- city and freight traffic and has reached its limits with a capacity of 24 trains per hour and direction (Figure 1). Disruptions on this section lead to delays in the entire Stockholm metropolis. To achieve a noticeable im- provement to the offer especially in suburban traffic it was essential to build a new parallel line. On the basis of the inner city situation the only possible solution was a tunnel. The new tunnel will double the capacity for the railway traffic through Stockholm. Construc- tion work has been completed and the tunnel is cur- rently being equipped with railway technology. The 6km long new underground line begins at the northern edge of Stockholm and branches off there from the northern approach to Stockholm C. The tun- nel passes beneath the city centre to the east of the existing line then passes under this line south of Stock- holmC below Riddarholmen. It then runs underground parallel to the existing line to the overground station Stockholms södra (Figure 2). The tunnel consists of a two-track tunnel tube blasted from the rock (Figure 3). Only beneath the Söderström between Riddarholmen and Söder Mälarstrand the tracks run through a floa­ ting rectangular concrete tunnel (Figure 4). There is a service tunnel housing important safety and telecom- munications technical equipment and other auxiliaries parallel to the railway tunnel (Figure 5). Two stations have been built along the line: the two-track station Odenplan and the four-track station Stockholm City, which is very close to the station Stock- holm C. There are also optimal possibilities to change to the crossing lines of the Metro ( T-Bana ) there. The line in the tunnel is equipped with a conductor rail and for the reduction of magnetic fields, with a booster transformer system. The cable-wound boos­ ter transformers have been installed at a distance of around 500m (Figure 6) and are directly connected to parallel running cables, which have been layed close together in a cable duct to minimise magnetic fields. The overhead line is directly connected to the booster feeder conductor at the booster transformer location. The booster return wire is connected with the tracks at the mid-point between the booster Figure 1: Suburban train on the railway bridge over the Söderström (Photos: Röhlig ). Figure 2: Overview of the position of the new tunnel ( yellow ) and the existing line ( blue ) [1].