The main line along the Rhine from the Netherlands is on the right bank, and so are the cities of the Ruhr. Köln (Cologne) is on the left bank, and so is the main station, Köln Hauptbahnhof. Some long-distance services to/from Düsseldorf reverse at Hauptbahnhof. That means they have to cross the famous but overloaded Hohenzollern Bridge, twice. As that became increasingly inconvenient, the little-used lower platforms at Köln-Deutz were upgraded to an ICE-station (Köln- Messe/Deutz Tief). This is a loop line, which takes the trains back out of Köln. It is not an elegant solution: trains pass within 900 m of Hauptbahnhof, but they don’t stop there.
The logical solution is a link line across the Rhine, north of Köln. It would connect the right-bank Düsseldorf – Köln line to the left-bank Neuss – Köln line. Trains from Düsseldorf would then enter Köln Hauptbahnhof from the north, cross the bridge, and continue southwards. And vice versa, on their northward journey.
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This is not an original proposal. The suggested alignment Langenfeld – Chorweiler is also self-evident. Markus Gröbe made a similar proposal. A possible alternative is a line between Köln-Longerich and Leverkusen-Rheindorf (shown in grey). It could run along the A1 Autobahn, but the area is more built-up, and the alignment more constrained.
The Rhine crossing from Langenfeld-Berghausen to Chorweiler would be 15 km long. That includes 5 km of extra tracks, alongside the line from Neuss, as far as Köln-Longerich. The new route is no longer than the existing route, through Köln Messe/Deutz. Both are 24 km long, from Langenfeld-Berghausen to the point where they cross again, at Deutz.
It is another 15,5 km, from Langenfeld-Berghausen to Düsseldorf Hbf: the total distance Düsseldorf – Köln would remain as it is, 39,5 km. Journey time should be about 17-19 minutes. The present ICE services which reverse at Köln Hauptbahnhof take 22 minutes, but it can take 38 minutes with a change of trains at Deutz.
There is another more difficult option: an alignment through the industrial areas of northern Köln to Leverkusen-Rheindorf, about 13,5 km long. It would start at the rail depot Köln-Betriebsbahnhof, just 1000m from Hauptbahnhof. It would be almost all in tunnel, under the suburbs of Nippes and Niehl, and under the A1 motorway bridge at Merkenich (Leverkusener Brücke). The line could probably surface, as it follows the broad Emdener Strasse.
Unlike the other variants, it could have an intermediate station. It could be located on the Emdener Strasse, or at Niehl, at the beginning of a surface section. It would serve northern Köln, with interchange to line 12 of the Stadtbahn Köln. The total route Düsseldorf – Köln would be only slightly shorter, but this variant would allow higher speeds, almost into Köln Hauptbahnhof.
See also: New cross-city tunnel-Köln.