DrNickTGM

We start off at Köln Hauptbahnhof, one of the biggest stations on the route. The station is an important local, national and international transport hub, with many ICE, Thalys and Intercity trains calling there, as well as regional Regional-Express, RegionalBahn and local S-Bahn trains. EuroNight and DB NachtZug night services also call at the station. It has frequent connections to Frankfurt by way of the Cologne–Frankfurt high-speed rail line, which starts in southern Cologne. On an average day, about 280,000 travellers frequent the station, making it the fifth busiest station in Germany.

The station is a hub of many Intercity Express and Intercity lines, mostly serving Cologne every hour or every two hours. Various high-speed services connect most cities in Germany as well as several neighbouring countries in a few hours. Thalys high-speed trains run from Cologne to Paris via Aachen, Liege and Brussels. An international Intercity Express service also operates every two hours during the day on the Brussels–Liege—Aachen–Cologne line, continuing towards Frankfurt. The station is also a hub for numerous Regional-Express and Regionalbahn services, mostly serving the station in Cologne every half-hour or hour, but sometime only every two hours.

Köln Messe/Deutz

Our first intermediate stop is Köln Messe/Deutz. It is an important railway junction for long-distance rail and local services in the Cologne district of Deutz in the German state of North Rhine-Westphalia. It is situated close to the eastern bank of the Rhine and connected via the Hohenzollern Bridge to Köln Hauptbahnhof, which is just a few hundred metres away. The Cologne Trade Fair grounds are directly north of the station, hence the Messe in the station's name. The Stadtbahn station of Deutz/Messe is nearby and connected by a pedestrian tunnel.

The station is a junction station, which has platforms on two levels: the high-level platforms are used by trains running in the east-west direction across the Hohenzollern Bridge to and from Köln Hauptbahnhof. The lower level (Köln Messe/Deutz tief) is used by trains running in a north-south direction bypassing the Hauptbahnhof from Köln-Mülheim station towards Troisdorf. It serves an important function in providing some relief for the Köln Hauptbahnhof bottleneck—some ICE services call at Köln-Deutz instead of Köln Hbf, eliminating the need for changing direction, while many regional trains from the west terminate here to prevent them blocking Köln Hbf.

The station is served by a International ÖBB NightJet Service that runs from Innsbruck to Dusseldorf, several ICE Services that head from Köln Hbf or Köln/Bonn Airport towards destinations such as Berlin, Munich and Stuttgart. Intercity and Regional services stop at the station as well. Local services also serve the station, mainly the Oberbergische Bahn, MittelrheinBahn, Rhein-Erft-Bahn, Erft-Bahn, and Rhein-Wupper-Bahn. With the Rhein-Ruhr S-Bahn Lines 6, 11 and Köln S-Bahn Lines 13 and 19 calling there as well.

Köln-Trimbornstraße

Before diverging into the main line once again, we'll take a look at the Köln/Bonn Airport loop's stations as well. Starting off with Köln-Trimbornstraße. It is situated at Kalk, Cologne in the German state of North Rhine-Westphalia on the Sieg and East Rhine Railways. It was opened on 2 June 1991 on a railway that was originally built as part of the Deutz–Gießen railway on 1 January 1859.

The station is served by the S12 and S13 lines of the Rhine-Ruhr S-Bahn. Both lines operate towards Cologne at 20-minute intervals, so together they provide a 10-minute interval S-Bahn service to Cologne. It is also served by the S19 service between Düren and Au (Sieg), running hourly (substituting for an S13 service). It is classified by Deutsche Bahn as a category 5 station.

Köln-Frankfurter Straße

Our next stop is Köln-Frankfurter Straße. It is a station situated at Gremberghoven, Cologne in western Germany on the Cologne Airport Loop and the Cologne–Overath railway. It was opened with the Cologne Airport loop on 13 June 2004. It is served by the S13 and the S19 services of the Rhine-Ruhr S-Bahn together run at 20-minute intervals on weekdays and every 30 minutes on the weekend. It is classified by Deutsche Bahn as a category 4 station.

Köln/Bonn Airport

Our main stop of this loop is the Cologne/Bonn Airport station. It is a station at Cologne Bonn Airport in the German state of North Rhine-Westphalia. It was built as part of the Cologne–Frankfurt high-speed rail line and opened in June 2004 on an approximately 15 kilometre-long airport loop. It is served by Intercity-Express (ICE), Rhine-Ruhr S-Bahn and regional services. The Cologne Bonn airport was the third German airport to have a connection to the ICE network after Frankfurt Airport and Düsseldorf Airport. The construction of the airport loop was, for the most part, financed by funds under the Berlin–Bonn Act, especially to improve connections from the Bonn/Rhine-Sieg region to the airport. Currently only Cologne and—Troisdorf in the Rhein-Sieg district—have direct connections to the airport via lines S13 and S19 of the S-Bahn, providing a service every 20 minutes on week days. 6 pairs of ICE also serve this station every day.

Porz-Wahn

The last stop on the Airport Loop before diverging onto the Main Line again, is Porz-Wahn. It is a railway station situated at Porz, Cologne in the German state of North Rhine-Westphalia on the Sieg and East Rhine Railways. It is served by the S12 and S13 lines of the Rhine-Ruhr S-Bahn. Both lines operate towards Cologne at 20-minute intervals, so together they provide a 10-minute interval S-Bahn service to Cologne. It is also served by the S19 service between Düren and Au (Sieg), running hourly and substituting for one of the S13 services. It is classified by Deutsche Bahn as a category 4 station.

Spich

The first station on the S-Bahn network after leaving the loop is Spich. It is a railway junction in the district of Spich of the town of Troisdorf in the German state of North Rhine-Westphalia, on the Sieg Railway. It is served by the S12 and S13. Both lines operate at 20-minute intervals, so together they provide a 10-minute interval S-Bahn service to Cologne. It is also served by the S19 service between Düren and Au (Sieg), running hourly and substituting for one of the S13 services. It is classified by Deutsche Bahn as a category 4 station.Troisdorf

The next station is Troisdorf. Troisdorf is a railway junction in the town of Troisdorf in the German state of North Rhine-Westphalia, where the line from Cologne separates into the East Rhine Railway to Neuwied and the Sieg Railway to Siegen. In addition to various regional rail services Troisdorf is served by the S12 and S13. Both lines operate towards Cologne at 20-minute intervals, so together they provide a 10-minute-interval S-Bahn service to Cologne. It is also served on working days by the S 19 service between Düren and Au (Sieg), running hourly and substituting for one of the S13 services. It is classified by Deutsche Bahn as a category 3 station.

The high-speed line also passes through Troisdorf, but without stopping. In the course of the construction of high-speed line, the three platforms were rebuilt and raised. Renovation or replacement of the station building is being planned.

Siegburg/Bonn

Continuing further up the line, we arrive at Siegburg/Bonn. The station is located in the town of Siegburg in the German state of North Rhine-Westphalia on the Cologne–Frankfurt high-speed rail line and the Sieg Railway. Its name is attributed to the fact that the station was rebuilt for the high-speed line in order to serve Bonn. It is connected to Bonn by the Siegburg line of the Bonn Stadtbahn every 10 or 15 minutes. ICE Services 42, 43, 45 and 49 as well as ICE International service 79 stop at Siegburg/Bonn, whilst the rest of the service pass through the station. The Ruhr-Sieg Express and S12 and S19 of the Rhein-Ruhr S-Bahn stop here as well.

Montabaur

Continuing further along is a station at the 89.1 kilometre point of the Cologne-Frankfurt high-speed railway and on the Limburg–Siershahn railway (Lower Westerwald Railway) in the German state of Rhineland-Palatinate. Known as Montabaur station. The station, which is served by regional and long-distance passenger services and freight traffic, is on the outskirts of the town of Montabaur. It is aligned parallel with Autobahn 3 (A3), which runs immediately to the north. ICE Services 41, 45 and 49, as well as the DreiLänderBahn trains running from Limburg (Lahn) to Siershahn stop here.Limburg Süd

And even further up ahead is Limburg Süd. The station in the town of Limburg an der Lahn, in the German state of Hesse. It is located in the Eschhöfer Feld in the district of Eschhofen at the 110.5 kilometre point of the Cologne–Frankfurt high-speed railway. Limburg Süd is the one of the two station in Germany that is served solely by Intercity-Express (ICE) services.

The majority of trains travelling between Frankfurt (Main) Airport Long-Distance Station and Köln Messe/Deutz Station run past Limburg Süd and Montabaur stations without stopping. The trains that pass through Cologne Central Station stop in both Limburg Süd and Montabaur stations before reaching Frankfurt (Main) Airport Long-Distance Station and vice versa.

Most parts of Cologne–Frankfurt high-speed rail line have steeper ascending and descending grades of 4%. This unique feature requires the higher power-to-weight ratio: ICE 3 with its power linear eddy current brakes is only train type licensed to operate on this railway: no other service, namely slower regional trains, is permitted. This makes Limburg Süd station one of the two stations in Germany to be served by high speed train services, the other being Frankfurt am Main Airport long-distance station.

Frankfurt am Main Airport

Our last intermediate stop of the line is Frankfurt am Main's airport. Specifically the long-distance station. The railway station at Frankfurt Airport in Frankfurt, Germany is served by long-distance trains, mostly ICE services running on the Cologne–Frankfurt high-speed rail line. It is the largest railway station serving an airport in Germany with about 23,000 passengers each day. The station is served by 210 long-distance trains daily, of which 185 are Intercity-Expresses. It and Limburg Süd Station are the only railway stations in Germany that are served exclusively by long-distance trains.

The station was opened in 1999 as part of the first part of the Cologne–Frankfurt high-speed line; the great majority of the high-speed line opened in 2002. It is 660 m long and 45 m high. It features a large dome containing a lounge area and a ticket hall, and is connected to the airport by a skyway that crosses the Autobahn 3. The Squaire, a one-billion-euro complex containing office space, hotels, convention centres and other facilities, has been built above the station. Nearby is Frankfurt Airport regional station which is located beneath Terminal 1 of the airport and which provides local S-Bahn services to Frankfurt, Wiesbaden and Mainz.Frankfurt Hbf

The last station on the line is Frankfurt am Main Hauptbahnhof. It is the busiest railway station in Frankfurt, Germany. Because of its location in the middle of Germany and usage as a transport hub for long and short distance travelling, Deutsche Bahn refers to it as the most important station in Germany. As for long-distance traffic, the station profits greatly from its location in the heart of Europe; 13 of the 24 ICE lines call at the station, as well as 2 of the 3 ICE Sprinter lines. To ease the strain on the Hauptbahnhof, some ICE lines now call at Frankfurt Airport station and at Frankfurt (Main) Süd instead of Hauptbahnhof. There are also long-distance night trains from Frankfurt, e.g. to Copenhagen, Berlin, Prague, Amsterdam, Zurich, Paris and Rom.

With regard to regional traffic, Frankfurt Hbf is the main hub in the RMV network, offering connections to Koblenz, Limburg, Kassel, Nidda, Stockheim, Siegen, Fulda, Gießen, Aschaffenburg, Würzburg, Mannheim, Heidelberg, Dieburg, Eberbach, Worms and Saarbrücken with fifteen regional lines calling at the main station.