The long-distance pair of tracks is designed for shared use by long-distance passenger and freight traffic from Ehrenfeld freight yard (line-kilometre 6) towards Aachen.
The S-Bahn section between Cologne and Sindorf also has two tracks.
Continuing towards Düren, single-track sections alternate with double-track crossing sections.
The entrance to Düren station (from Merzenich station) is single-track.
The long-distance tracks are designed for operations at 250 km/h and the S-Bahn tracks for 120 km/h.
From Merzenich station east of Düren (line-kilometre 34.480), the design speed of the long-distance tracks is 220 km/h, from line-kilometre 38.0 it is 200 km/h and from line-kilometre 39.6 it is 160 km/h.
The S-Bahn was designed for a 20-minute cycle (during peak hour) with the possibility of shorter cycles.
53 S-Bahn trips per day and direction were planned.
Regional trains running on the long-distance tracks between Cologne and Düren still stop in Horrem and Cologne-Ehrenfeld.
No plans were made to run the S 6 to Horrem and thus create a ten-minute cycle between Horrem and Cologne.

In a second construction phase, the section between Düren and Langerwehe is to be upgraded for speeds of up to 200 km/h.
The subsequent section via Eschweiler to Aachen is to be upgraded for 140 km/h.
Currently, speeds of up to 120 km/h are possible between Eschweiler and Stolberg, although sometimes only up to 110 km/h.
Top speeds of 140 or 160 km/h are already permitted on the rest of the line.
It should be possible for trains to pass through Düren station at 200 km/h after completion of the second stage of construction.
In the final state, it should be possible to run at a minimum of 200 km/h over an almost 50 km-long section between Cologne and Langerwehe.

The investment framework plan for federal transport infrastructure of 2010 (Investitionsrahmenplan bis 2010 für die Verkehrsinfrastruktur des Bundes) specified total costs of €951.7 million (as of 2006) for new construction and upgrading between Cologne and the German-Belgian border (including the Busch Tunnel).
€769.8 million of this was spent up to 2005.
Federal funds totaling €88.9 million were invested between 2006 and 2010.
Beyond this period, there is a need for finance of €93.0 million (federal funds from 2011, own funds of Deutsche Bahn and contributions from third parties from 2006).

In November 2008, additional investments in the Aachen–Stolberg–Eschweiler section were approved as part of an economic stimulus package.
It was planned that the Aachen-Rothe Erde–Stolberg section would be partially upgraded to three tracks from 2010.
This project has not yet been implemented.
Only the Aachen-Rothe Erde station has been modernised.
Due to the construction delay, the European Commission cut funding for the project by €2.9 million at the end of 2010.
In June 2010, EVS Euregio Verkehrsschienennetz (EVS) acquired Stolberger Hauptbahnhof including the entrance building.
Only the dispatcher signal box and the mainline through tracks remained the property of Deutsche Bahn.
The EVS started the reconstruction of Stolberg Hauptbahnhof in 2012 and the height of the main platform was increased to 760 millimetres.

In 2017, Deutsche Bahn began construction work on the island platform on the mainline through tracks at Stolberger Hauptbahnhof.
The existing underpass is to be replaced by an overpass with lifts.
The work was expected to take until the middle of 2019.
Construction work on the Upgraded line 4, II.
upgrade phase, 1.
construction stage project at Eschweiler Hauptbahnhof began in 2018.
Platforms at the Hauptbahnhof have been raised to 76 cm and barrier-free access has been created to the island platform via lifts and the two passing tracks (platform 1 and 4) have been extended to a useful length of 750 m. The relay interlocking has been replaced by connecting the station to a computer-based interlocking and the last level crossing between Cologne and Aachen at Jägerspfad in Eschweiler is to be closed.
Work in Aachen should also begin in 2019.
In the district of Eilendorf, the third track is
The long-distance pair of tracks is designed for shared use by long-distance passenger and freight traffic from Ehrenfeld freight yard (line-kilometre 6) towards Aachen. The S-Bahn section between Cologne and Sindorf also has two tracks. Continuing towards Düren, single-track sections alternate with double-track crossing sections. The entrance to Düren station (from Merzenich station) is single-track. The long-distance tracks are designed for operations at 250 km/h and the S-Bahn tracks for 120 km/h. From Merzenich station east of Düren (line-kilometre 34.480), the design speed of the long-distance tracks is 220 km/h, from line-kilometre 38.0 it is 200 km/h and from line-kilometre 39.6 it is 160 km/h. The S-Bahn was designed for a 20-minute cycle (during peak hour) with the possibility of shorter cycles. 53 S-Bahn trips per day and direction were planned. Regional trains running on the long-distance tracks between Cologne and Düren still stop in Horrem and Cologne-Ehrenfeld. No plans were made to run the S 6 to Horrem and thus create a ten-minute cycle between Horrem and Cologne.
In a second construction phase, the section between Düren and Langerwehe is to be upgraded for speeds of up to 200 km/h. The subsequent section via Eschweiler to Aachen is to be upgraded for 140 km/h. Currently, speeds of up to 120 km/h are possible between Eschweiler and Stolberg, although sometimes only up to 110 km/h. Top speeds of 140 or 160 km/h are already permitted on the rest of the line. It should be possible for trains to pass through Düren station at 200 km/h after completion of the second stage of construction. In the final state, it should be possible to run at a minimum of 200 km/h over an almost 50 km-long section between Cologne and Langerwehe.
The investment framework plan for federal transport infrastructure of 2010 (Investitionsrahmenplan bis 2010 für die Verkehrsinfrastruktur des Bundes) specified total costs of €951.7 million (as of 2006) for new construction and upgrading between Cologne and the German-Belgian border (including the Busch Tunnel). €769.8 million of this was spent up to 2005. Federal funds totaling €88.9 million were invested between 2006 and 2010. Beyond this period, there is a need for finance of €93.0 million (federal funds from 2011, own funds of Deutsche Bahn and contributions from third parties from 2006).
In November 2008, additional investments in the Aachen–Stolberg–Eschweiler section were approved as part of an economic stimulus package. It was planned that the Aachen-Rothe Erde–Stolberg section would be partially upgraded to three tracks from 2010. This project has not yet been implemented. Only the Aachen-Rothe Erde station has been modernised. Due to the construction delay, the European Commission cut funding for the project by €2.9 million at the end of 2010. In June 2010, EVS Euregio Verkehrsschienennetz (EVS) acquired Stolberger Hauptbahnhof including the entrance building. Only the dispatcher signal box and the mainline through tracks remained the property of Deutsche Bahn. The EVS started the reconstruction of Stolberg Hauptbahnhof in 2012 and the height of the main platform was increased to 760 millimetres.
In 2017, Deutsche Bahn began construction work on the island platform on the mainline through tracks at Stolberger Hauptbahnhof. The existing underpass is to be replaced by an overpass with lifts. The work was expected to take until the middle of 2019. Construction work on the Upgraded line 4, II. upgrade phase, 1. construction stage project at Eschweiler Hauptbahnhof began in 2018. Platforms at the Hauptbahnhof have been raised to 76 cm and barrier-free access has been created to the island platform via lifts and the two passing tracks (platform 1 and 4) have been extended to a useful length of 750 m. The relay interlocking has been replaced by connecting the station to a computer-based interlocking and the last level crossing between Cologne and Aachen at Jägerspfad in Eschweiler is to be closed. Work in Aachen should also begin in 2019. In the district of Eilendorf, the third track is
Cologne–Aachen high-speed railway