This proposed high-speed rail line (HSL) would connect the new Berlin Brandenburg Airport (known as BBI), to the main Berlin – Warsaw line. It would join that line near Erkner, and run alongside it to Frankfurt, on the Oder river. It is an extension of the proposed new line from Potsdam to the airport. Since the idea is evident from a map, this line has probably been proposed before, but apparently never at official level.
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The official plans for the new airport do include a new link eastward, but only to the Berlin – Cottbus line, the Görlitzer Bahn. In fact, part of this alignment exists already, as a freight siding into the existing airport. The Görlitzer Bahn is 7 km from the airport terminal.
Click to enlarge: the planned eastern exit line for the airport terminal, under construction.
The eastern airport line is primarily intended for long-distance trains, which make a diversion to serve the airport (the S-Bahn will not use this section). The diversion is inevitable, because the airport is not on a radial line. For instance trains to Dresden would exit Berlin to the south-east, via Karlshorst, turn south-west through the airport, and then south over the Dresdner Bahn. Conversely, the Görlitzer Bahn to Cottbus would be reached from the Dresdner Bahn, via the airport.
Apart from these trains, the utility of the airport line is limited, because it is not on a through route. Eastwards, it only connects to the Görlitzer Bahn. The proposed HSL would make it part of a longer through route, connecting it to a European HSL axis. The next station to the east would be Frankfurt (Oder), 74-75 km from the airport station.
The HSL would start from the airport exit line, either at the edge of the terminal zone, or just before its junction with the Görlitzer Bahn. The HSL would cross the Görlitzer Bahn, in forest south of the built-up area. It would join the alignment of the existing Frankfurt line south of Erkner. This is also beyond the built-up area (Erkner is the terminus of S-Bahn line S3).
The terrain is not a problem, elevation ranges from 30m to 45m. However, the line would cross the lakes and forests of the Regionalpark Müggel-Spree. This is the largest recreational zone on the eastern side of Berlin, and it was annexed to Berlin in 1920, partly because of this. The rail line would cross a shallow lake on the Dahme river (Langer See), about 1 km north of the village of Schmöckwitz, and pass close to another lake (Seddinsee)
Click to enlarge: the lake cluster around Schmöckwitz, with Berlin in the background. The HSL would run left to right, at about two-thirds of the image height. Image by Matthias Renner under Creative Commons 3.0 licence.
A tunnel is the only option here, possibly with short surface sections. The lakes are glacial features, and the whole area is part of the Berlin meltwater channel. The geology would determine the alignment of tunnels here, so no exact alignment is given for the HSL. The section from the airport to the junction with the Frankfurt line would be about 20 km long. Of that, about 10 km passes through the protected zone.
The line would surface after crossing the Spree, south of Erkner. The junction with the existing Frankfurt line would be close to the Berlin ring Autobahn, about 4 km beyond Erkner station. This is the Niederschlesisch-Märkische Eisenbahn, originally built to serve Silesia rather than Warsaw.
From the junction, the HSL can closely follow the existing line. It consists of straight sections, several kilometres long, with curves between them. Most of it runs through forest: the only large village is Fürstenwalde, but the alignment there is wide enough for extra tracks.
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At Frankfurt, the HSL could follow the existing approach into the station. From there, the existing alignment across the River Oder is curved, and unsuitable for high speed. A new alignment could follow the motorway, but the station would be at the edge of the built-up area, and there is a 70m drop to the river. A new alignment starting just outside the station might be possible, but it would require a bridge height of about 40 m, and a viaduct across the flood plain.
The HSL east of Erkner could also be used by high-speed trains from central Berlin, using the east-west surface line through Berlin Hauptbahnhof. The main ICE and Intercity services at Berlin Hauptbahnhof use its north-south underground platforms. A connection to the proposed HSL would require upgrading of the existing route through Ostkreuz and Karlshorst. In any case, trains from Frankfurt could also reach Berlin Hauptbahnhof from the south, via the airport and the Dresdner Bahn.