This proposal would extend the alignment of S-Bahn line S25, from Teltow Stadt to Potsdam. Although the S25 is a radial line, the new section would also form a tangential line, on the southern edge of Berlin. That would be a logical compliment to the proposed new line Potsdam – airport BBI, which would carry no local traffic.
Click to enlarge: S-Bahn lines between Berlin and Potsdam, with two possible alignments for an extended S25 line. CC 2.0 licence, modified from network map by Maximilian Dörrbecker.
The proposal would create a second S-Bahn line from Potsdam into Berlin, an alternative to the line via Wannsee. There is third possible route, the roughly parallel Potsdamer Stammbahn. That was the original main line to Potsdam: it once had a temporary S-Bahn shuttle Zehlendorf – Düppel, but never a full S-Bahn service to Potsdam. (An S-Bahn line has recently been proposed, but this is not in any official plans). The Stammbahn and the Wannseebahn, and a northern alignment of the new line, converge at Potsdam Griebnitzsee station. A possible southern alignment (light green dotted line) would join the others at Potsdam Hauptbahnhof.
There is one more former S-Bahn line in the area: the old Wannsee – Stahnsdorf branch, at right angles to the other lines. An S25 extension would give Stahnsdorf a better connection into central Berlin.
There are no current plans for a long extension of the S-Bahn line S25 to Potsdam. However, there is a proposal for a tram line on a very similar alignment, via Stahnsdorf. A full tangential function for the new S-Bahn line would also require a connection eastward, through Marienfelde or Lichtenrade. It would not necessarily be an S-Bahn line: a light metro, for instance Zehlendorf – Buckow, might be better. This eastward connection is not considered further here.
The present S25 uses the Anhalter Vorortbahn alignment. Its extension beyond Teltow was already planned in the 1930’s, but apparently not to Potsdam. Construction work began, but was later abandoned: the incomplete alignment is still visible. The plan was apparently to connect it to the Wannsee – Stahnsdorf branch, meaning that trains from Berlin would turn back north, to reach their terminus.
The proposal here has a more logical route. It starts in Potsdam – with 155 000 inhabitants a far better terminus than Teltow or Wannsee. Trains would use the existing S-Bahn line, from Potsdam Hauptbahnhof to Potsdam Griebnitzsee. The new alignment would continue east through the forest, along the line of the Berlin Wall (Mauerstreifen).
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The fast line to BBI airport would turn south-east, to pass south of Stahnsdorf. The S-Bahn line would run approximately parallel to the Teltow Kanal. After crossing the A115 Autobahn, it would enter Stahnsdorf (14 000 inhabitants). The alignment would follow the Alte Potsdamer Landstrasse, Wannseestrasse and Bäkedamm. The housing density is low, and much of the line can run on surface, or on viaduct. The section in the centre, and the station, would be in tunnel. There are several possible alignments, which require minimal demolition: the line would turn south-east under the park (Bäkewiese).
The line would exit the built-up-area, parallel to Ruhlsdorfer Strasse or Separationsweg. (Most of the housing in Stahnsdorf is south of the old village). It would then join the never-completed 1930’s alignment, which runs in a straight line, 800 m south of the village centre.
Click to enlarge: possible alignments in Stahnsdorf…
In Teltow (population 22 000), there would be a second station at the Iserstrasse. The line would continue over the 1930’s alignment, to join the existing line at Teltow Stadt station, 800 m from the historic centre. The alignment in Teltow is at the southern edge of the built-up area, and it could be improved by a tunnel section (light blue dotted line). The second station would then be at the crossing Potsdamer Strasse / Iserstrasse, in the main employment zone.
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The new section from Griebnitzsee to Teltow is almost straight, and would be about 10 km long. Including existing lines, the extension from Teltow Stadt to Potsdam Hauptbahnhof would be 14-15 km long.
There is a possible southern alignment in Potsdam, which would join the other between Stahnsdorf and Teltow. It would run alongside the Nuthestrasse, which is in fact a section of urban motorway linking the Autobahn to the centre of Potsdam. This alignment would be relatively easy to build, with stations at Horstweg, Neuendorfer Strasse, and Gaustrasse (on the tramline to Drewitz, near a large shopping centre). However, only that last station is close to housing and shops, and the alignment as a whole would be longer. The disadvantages probably outweigh the benefits of this alignment.
Journey time from central Berlin (Friedrichstrasse), via line S25 to Teltow Stadt, is currently 27 minutes. With four intermediate stations, the extra 14 km to Potsdam Hauptbahnhof would add about another 12-14 minutes, making about 40 minutes in total. Via Wannsee (S7), journey time from Friedrichstrasse is 41 minutes. The extended line is not intended as an express service: the fastest option for that is an express regional line, over a reopened Potsdamer Stammbahn, which could offer a 20-minute journey to Berlin Hauptbahnhof.