Revised: HSL Maastricht – Aachen

Revised with new maps: High-speed rail line Maastricht – Aachen.

Advertisements
Revised: HSL Maastricht – Aachen

High-speed rail line Maastricht – Aachen

This proposed high-speed line (HSL) complements the reactivation of the old line Aaachen-Richterich-Simpelveld-Valkenburg-Maastricht, opened 1853 and closed 1992. The reopened line would form part of the proposed urban-regional metro Aachen (S-Bahn Aachen). The HSL would provide a fast service between the city centres: The Aachen urban region has 540 000 inhabitants, with 240 000 in Aachen itself. The city of Maastricht has 122 000 inhabitants. The HSL would also connect to other intercity services from Aachen and Maastricht.

maas-aachen-HSL

The proposed line makes sense primarily in the context of the proposed high-speed line Hasselt – Maastricht and a high-speed service from Antwerpen to Hasselt. Together, the proposals create a new east-west high-speed route, from Antwerpen to Aachen.

ant-maas

The proposed line uses part of the alignment of the former Limburgsche Tramweg-Maatschappij (LTM), a steam-tram line from Maastricht to Vaals, opened in 1925. East of Gulpen, the new HSL would have a similar alignment to a possible Gulpen – Vaals – Aachen link, an urban-regional line (S-Bahn). Combined construction of both lines would be difficult: the best option is a direct HSL, together with reactivation of the old line Maastricht – Aachen, with urban-regional services via Valkenburg.

The new line would start at Maastricht Station, on the right bank of the Maas (opposite the historic city centre). The high-speed line from Hasselt would approach the station from the north, in tunnel under the Maas.

The proposed HSL from Hasselt…

hsl-hasselt-maastricht

 
Maastricht station would need redesign as a through station: at present, it is a terminal station for trains from the north. Immediately south of the station area, the rail line is constricted: the prominent Church of the Sacred Heart blocks expansion of the rail area here. Nevertheless, there is sufficient room for extra tracks, if the road in front of the church is closed. If the new platforms begin at the station building, there is also sufficient room for a grade-separated junction at the south end of the station. The road tunnel Akerstraat / Scharnerweg can probably remain in use.

South of the station, the new line to Aachen would drop into tunnel, and turn east. With the construction of the A2 motorway tunnel through Maastricht, an exit line under the Akersteenweg is no longer possible. The new line would pass under the A2 just as it enters the tunnel section, at the Europaplein junction.

The motorway tunnel entrance under construction: parallel rail line left, sports field right…

maastricht-a2-tunnel

 
It would then pass through Heer, at first in a cut-and-cover tunnel (under the sports field). This neighborhoud consists of an old village street, surrounded by low-rise housing. Because the terrain slopes upward, the line can enter a bored tunnel about 500 m from the motorway, minimizing local demolition. With the southern alignment, in green, a bridge over the motorway might also be possible.

Alternatives for an exit line: basiskaart van Jan-Willem van Aalst, onder CC3.0 licentie

exit-heer-maastricht

 
As it leaves the built-up area of Maastricht, the line would climb 80 m toward the plateau, surfacing just east of Cadier en Keer. The 5-km tunnel would be comparable with the Tunnel de Soumagne at Liège, which has an identical function. (It carries the Liège – Aachen HSL out of the Maas/Meuse valley, to the plateau on the eastern side).

Between Cadier en Margraten, the HSL alignment would approximately parallel the N278, on the south side of the road. The main road climbs about 40 metres, in the 3 km between the two villages. Although the road through Margraten is straight, and just wide enough for a cut-and-cover tunnel, the best option seems to be an alignment south of the built-up area.

Between Margraten and Gulpen, the road falls 70 metres. The old steam tram avoided this slope, by diverging to the south, crossing the Gulp valley on a viaduct at Euverem, and entering Gulpen from the south-west. The new line will not enter Gulpen, but it would use a similar solution. It would cross a descending viaduct near the campsite at Euverem, and cross the Gulp valley. The valley floor is at about 105 m altitude. It would enter a tunnel, under the ridge between the Gulp and Geul valleys.

euverem
 

The line would emerge from tunnel south-west of Partij, and pass south of Partij and Wahlwiller, to rejoin the alignment of the N278. In theory, a single base tunnel is possible, from Maastricht to the Geul valley at Partij. It would be about 15 km long.

From Partij to Vaals, the alignment would be identical to that of the possible Gulpen – Vaals – Aachen link. The constraints are the same, and the best solution is to follow the N278. The line would pass just south of Nijswiller, with a tunnel under the low ridge between Wahlwiller and Nijswiller. It would rejoin the route of the N278, at its junction with the N281.

gulpen-n281
 

From here to Vaals, the constraints include a narrow section of the valley (Selzerbeek stream, Senserbach in German), and historical building such as the Benedictine Abbey Benedictusberg and the old centre of Lemiers. The N278 runs in a straight line, the gradient is acceptable: a rail line is possible beside the road, or in some places under the road. The road through Lemiers, which avoids the historic village core, is wide enough for a shallow tunnel.

lemiers
 

From Lemiers, the road climbs 40 m up the flank of the valley, in less than 2 km, to the edge of Vaals. The old tram line followed an easier gradient, nearer the Selzerbeek, on the north side of Vaals. For high-speed trains the gradient into Vaals is not a problem, and the line could go in shallow tunnel through the village (thin blue line). The main street does curve in Vaals itself, which might restrict speed.

The alignment in Vaals would also be dependent on the route eastwards, to Aachen Hauptbahnhof (6 km due east). One option is to follow the main road – Vaalser Strasse, Bundesstrasse 1 – at least as far as the junction with the Amsterdammer Ring. The main road dips and curves, as it crosses the Senserbach (barely visible here), and curves again about 400 m east. However, there is enough open space is enough to allow the line to emerge from tunnel, and enter another tunnel (red dotted line), under the houses of Vaalserquartier. Another option is a long tunnel (white dashed line) under the southern half of Vaals, which is about 20-30 m higher than the main road. This tunnel would join the alignment of the freight rail line Aachen – Montzen – although this line does not go to Aachen Hauptbahnhof, and another connecting tunnel would be required

door-vaals
 

Near the western cemetery (Westfriedhof), the Vaalser Strasse crosses the Aachen – Montzen line. Here, all variants would enter a tunnel – the exact alignment and portal depends on the alignment through Vaals. The tunnel would surface close to the main station (near Weberstrasse). Because of the terrain, the built-up areas, and the crossings with roads and rail lines, a single long tunnel from Vaals might be the best option.

vaalser-portal
 

The exit point of the tunnel is a problem, in this densely-built urban area. Aachen Hauptbahnhof also has a restricted location, which could be improved (on the west side), by moving the northern boundary of the track area (red line), and re-aligning some of the tracks (blue lines).

portal-aachenhbf
 

The total length of the line from Maastricht to Aachen would be about 32 km. Although the line is too short for very high speeds, the section Cadier – Vaals could be aligned for 150 km/h to 180 km/h. A journey time of under 20 minutes is certainly feasible.

High-speed rail line Maastricht – Aachen

Herzogenrath-Stolberg S-Bahn line

The ring freight line from Herzogenrath to Stolberg has a winding route via Alsdorf, but it is the only ‘orbital’ or ‘tangential’ line around Aachen region, roughly 12 km from the city centre. The section from Herzogenrath to Alsdorf-Annapark has been reopened for passengers, , as part of the Euregiobahn network. Reopening of the rest of the line for passenger services is planned, but Euregiobahn is a light-rail network with low service frequencies.

The proposal here goes further: a full S-Bahn service, on a shorter and faster route, as part of the proposed urban-regional metro network around Aachen.

herzogenrath-stolberg

It would be a logical extension of the proposed Maastricht – Heerlen – Herzogenrath urban-regional (S-Bahn) line.

The line would turn south-east from the existing line, south of Herzogenrath station – the freight line to Stolberg passes north of Herzogenrath. The exact alignment is not shown here: a tunnel is inevitable, to climb 40 m from the valley of the river Wurm.

herz-bardenberg

The line would pass just north of Bardenberg, and near Gewerbegebiet Weiweg it would join the alignment of the former Aachen-Nord – Jülich line. It would then reach the former station at Würselen, which can be reopened. Here the line met the Kohlscheid – Stolberg freight line, and the S-Bahn would follow that line out of Würselen station. The alignments near Würselen are intact, but partly in use as a ring road (Willy Brandt Ring). In most places, there seems sufficient space for a line next to the road, but the junctions will need reconstruction.

willybrandt-ring

The Aachen-Nord – Jülich line is also a candidate for reopening, as a Euregiobahn line. If it is reopened as a light-rail line, or possibly as an urban tram, then Würselen would be an interchange station.

After Würselen, the S-Bahn line would serve a reopened Weiden Station, and then follow the original alignment of the Kohlscheid – Stolberg line. This section (still in use) was re-routed in 1939 for construction of the Autobahn to Aachen. The later Autobahnkreuz Aachen (A4 / A44) was built on the old alignment, but only a short tunnel is needed to restore it.

ak-aachen

Close to the main Aachen – Köln line, the S-Bahn line would join the alignment of the freight line from Herzogenrath, into Stolberg station. In any case, there is also an older alignment on the north side of the main line, which could take the S-Bahn to Stolberg Hbf, without any shared track (orange line). The ‘Hauptbahnhof’ has a peripheral location, but it is on the main line, and it is the interchange point for the local line through Stolberg (originally part of the Vennbahn).

ak-stolberg

The new S-Bahn line would terminate at Stolberg, about 11 km from Herzogenrath. The logical service pattern is an extension of the proposed Maastricht – Heerlen – Herzogenrath service, creating a long orbital line relative to Aachen.

Herzogenrath-Stolberg S-Bahn line

Maastricht – Heerlen – Herzogenrath line

The proposed urban regional metro around Aachen would realign the existing local services in southern Limburg, and replace the euregiobahn network. It would include a direct line Aachen – Heerlen, mostly in tunnel (orange line on the map).

A new link line Kohlscheid – Kerkrade would carry a second Aachen – Heerlen service. It is shown in blue: there are several options for the route through Kerkrade.

Click to enlarge…

Regional metro around Aachen

The remaining local service from Maastricht to Heerlen via Valkenburg can then be extended to Herzogenrath (line in red on the map). It would use the existing line from Landgraaf, via Eygelshoven-Markt, to Herzogenrath (built as part of the Sittard – Herzogenrath line in 1896.) This line is at present single-track and not electrified. Double-tracking and electrification is planned, for an Intercity service Eindhoven-Aachen.

At Merkstein, the single-track line joins the Aachen – Mönchengladbach line. It is at present underused, but increased traffic would require a grade-separated junction here, unless the line from Heerlen has its own tracks into the station. Bahnhof Herzogenrath has enough space for an extra terminal platform.

On the section across the river Wurm/Worm, the former Haanrade Station could be reopened. Despite the name, it was in fact in Eygelshoven, at the former Julia Mine (at Wolfsweg). The former mine is now an industrial zone.

The line Maastricht – Heerlen – Herzogenrath is 42 km long.

Maastricht – Heerlen – Herzogenrath line

Re-opening line Maastricht – Aachen

The Euregio Maas-Rhein has about 4 million inhabitants, and three large cities: Liège, Maastricht and Aachen. The last two have no direct rail link: it was closed in 1992. The Maastricht – Aachen railway was built in 1853, but at present it is used only for internal services in the Netherlands: Maastricht – Valkenburg – Heerlen. These trains use a connecting line from Schin op Geul to Heerlen, built in 1915. The lines follow river valleys through the plateau of South Limburg.

Maastricht – Aachen 1901, click to enlarge: base map from Uni Greifswald

Maastricht-Aachen-1901

 
In European perspective, the line to Aachen is more important than the Maastricht-Heerlen line. The Aachen urban region has 540 000 inhabitants, with 240 000 in Aachen itself. The city of Maastricht has 122 000 inhabitants. Aachen is on the existing high-speed route from Paris and Brussels to Köln.

The basic proposal is to re-open the closed section from Schin op Geul to Richterich, to double-track the section from Wijlre-Gulpen to Richterich, and construct a grade-separated junction at Richterich with the line from Mönchengladbach.

Re-opening rail line Schin op Geul - Simpelveld - Richterich - Aachen.

 
Other proposals for the region would affect the function of the line, and therefore determine how much new infrastructure is needed.

Context: other proposals

The re-opened line could connect to the proposed tunnel under central Aachen, the heart of a regional metro (S-Bahn) network. The tunnel is intended to connect to a Sittard-Heerlen-Aachen S-Bahn line. That line would use part of the disused alignment from Maastricht, joining it at Vetschau.

To avoid overloading the line into Aachen, the S-Bahn from Heerlen might use a new tunnel under Laurensberg. In that case, there might be two parallel Laurensberg tunnels, since a new tunnel into Aachen is also essential for the proposed high-speed rail line Sittard – Aachen. A Laurensberg tunnel would shorten the Maastricht – Aachen line by about 1500 m.

New Aachen regional metro tunnels

 
In all those cases, all trains would pass through Aachen West. The proposed high-speed line Maastricht – Aachen would not use any of the old alignment, and would not pass Laurensberg or Aachen West. It would run further south, about 2-6 km from the original Maastricht – Aachen line, and enter Aachen Hbf from the west.

HSL Maastricht – Aachen…

maas-aachen-HSL

 
The HSL Maastricht – Aachen would form an extension of the proposed HSL Hasselt – Maastricht, part of a high-speed route from Antwerp. At Maastricht there would also be interchange with a high-speed route along the Maas/Meuse, with a HSL from Liege, and a four-track line north to Sittard connecting with a HSL to Eindhoven, and a Maas HSL to Nijmegen.

As an alternative to a new Maastricht – Aachen HSL, the re-opened line could be upgraded to carry an express service. The upgrading would consist mainly of extra tracks through stations (between Maastricht and Schin op Geul), and a grade-separated junction at Schin op Geul station. That would allow overtaking of stopping trains, but not high speeds. The Maastricht – Aachen railway was not built for speed, and upgrading for high speed is pointless – a completely new line would be easier to build.

Pattern of services

At present the line carries four trains per hour. An all-stations train to Heerlen, every 30 minutes, continues to Kerkrade. There is a faster Maastricht – Heerlen service every 30 minutes, stopping at Meerssen and Valkenburg: some off-peak trains run on weekdays only. Valkenburg is the main tourist centre east of Maastricht, and a transfer point for regional bus lines.

With re-opening of the Aachen line, the Heerlen service could run non-stop to Valkenburg. Since the all-station trains take only 8 minutes longer, that service could replace the existing fast trains. With an upgraded line to Schin op Geul, and double-tracking of the Heerlen branch, journey time would be only slightly longer. That would be compensated by higher frequencies on a regional metro network – at least every 15 minutes.

15 minutes is also the minimum frequency for a Maastricht – Aachen regional metro line. Without the proposed HSL, a separate fast service would be needed on this route. It would also stop at Valkenburg, preferably at a four-track station. Other stations often have room for extra tracks: they were laid out for coal trains, when this was a mining region.

Maastricht to Schin op Geul

The line to Aachen diverges from the Maas Valley Line, about 3 km north of Maastricht Station. The four tracks out of the station are operated as parallel double-track lines, and this section needs to be reconstructed, as part of the four-track line to Sittard. The old halt at Nazareth-Limmel could be re-opened as a new station. The recent Maastricht Noord station, a P+R station at the edge of the city, can be retained, but it would need a new layout. A grade-separated junction is essential, just north of this station.

The line from the junction to Schin op Geul is double-track and electrified. There are three intermediate stations on this section: Meerssen, Houtem-St. Gerlach, and Valkenburg. The halt at Rothem was closed in 1935. A new station here, only 600 m from the platforms at Meerssen, can not be justified.

Maastricht – Rothem – Meerssen: base map by Jan-Willem van Aalst, CC3.0 licence

rothem

 
The line might be slightly re-aligned from the junction to Meerssen, but that is not strictly necessary. There is room for an extra track on the south side at Meerssen Station (toward Aachen), and on the north side at Houthem. After Meerssen, the line follows the north flank of the Geul valley.

The commuter village of Meerssen has 5700 inhabitants, but the next station at Houthem-St. Gerlach serves only about 1500. If the line was built today, the village would not have a station, but there is no reason to close it. The small town of Valkenburg has 5800 inhabitants, but with extra traffic as a tourist destination.

Houthem – Valkenburg: base map by Jan-Willem van Aalst, CC3.0 licence

Houthem-Valkenburg

 
The station should be reconstructed as an interchange, preferably with a new layout. The station building is the oldest surviving in the Netherlands, but there is sufficient space on the western side for two island platforms.

Re-opening Schin op Geul to Richterich

At the next station, Schin op Geul, the line to Heerlen turns north-east. The next section, to Simpelveld, is in use by the museum line ZLSM and could easily be reopened. (The ZLSM trains start at Valkenburg, and use the electrified section for 3 km). The station at Schijn op Geul is located in the V-shaped junction between the electrified line and the museum line, on the hillside above the village (1500 inhabitants). A grade-separated junction is preferable here, but difficult to construct. Possibly the platform for Heerlen could be placed in a cutting, passing under the existing car park.

station-schin-geul

 
Another alternative is to shift the ZLSM platforms to the south, to allow four tracks just west of station. That would allow a grade-separated junction west of station (at the chalet park).

The newly electrified line (ex-ZLSM) would have stations at Wijlre, Eys, Simpelveld, and Bocholtz. The station at Wijlre (population 2000) once had a tram connection to Gulpen, on the other side of the valley, but realistically it can not serve that village. An additional 2-km link to Gulpen is described separately: it would be an alternative to the Maastricht-Aaachen bus line along the N278.

After Wijlre, the line crosses the valley of the Eyserbeek stream, on a large embankment. For a double-track line, a parallel replacement viaduct is an option here. The old Eijs- Wittem station is on the hillside above the village, but there is no better location. Again, the village is just large enough to justify a station (1450 inhabitants).

The line on the hillside above Eys/ Overeys…

Eys

 
Simpelveld, on the other hand, has 5200 inhabitants, and the station can easily be reconstructed with through tracks, and possibly for interchange with the branch to Kerkrade (also in use by the ZLSM). The large station area is a reminder of the former coal traffic in the region, and it is close to the centre of the old village. The old halt at Bocholtz is also very close to the village centre, but has limited space on a curving line. By lowering the road here, taking advantage of the terrain, there would be enough space for a double-track line and platforms.

Simpelveld – Bocholtz: base map by Jan-Willem van Aalst, CC3.0 licence

Simpelveld-Bocholtz

 
Beyond Bocholtz, the line carries no traffic. The ZLSM once ran trains to a simple halt at Vetschau, just over the border on the edge of Aachen: this track is still usable. Beyond that halt, on the Laurensberger Strasse, the line is is abandoned and overgrown. Nevertheless the alignment is still free, and has enough space for two tracks. (This section will be used by the planned Via Avantis light-rail line, but that would not prevent trains from Maastricht from using it. The current status of that project is unclear).

The main problem within Aachen, is the construction of a grade-separated junction at Richterich, with the line from Mönchengladbach. Space is limited, and the line is curved. A new station in Richterich is also planned, but north of the junction with Maastricht line. The problematic junction would be avoided by using a new Laurensberg tunnel.

Journey times

At present the Maastricht-Aachen journey takes one hour, changing at Heerlen to a Euregiobahn train. With restoration of the line through Vetschau and Richterich, and the existing line from there to Aachen Hauptbahnhof, the line would be 38 km long. With 13 intermediate stops, and S-Bahn type trains, journey time would be about 45 minutes. Using the Laurensberg tunnel, the line would be 1500 m shorter and have one less stop.

If trains used the proposed tunnel under central Aachen, that would shorten the route to the city centre by another 1500 m, and save another stop. The Maastricht – Aachen route would then be close to 35 km long, and journey time could be 40 minutes.

Re-opening line Maastricht – Aachen

Urban-regional metro Aachen

This is an initial alignment proposal, for an urban-regional metro (S-Bahn) in and around Aachen. A new central tunnel, from the Aachen-West marshalling yard to Rothe Erde, would effectively duplicate the existing surface route, passing under the historic centre. At present there is insufficient capacity for an S-Bahn service – the local Euregiobahn can only operate because service frequency is low. The tunnel would be used by trains from several branches, extending up to 35 km from central Aachen. From the north, access is from the Mönchengladbach line, and from a new Vaals line (via the university complex at Melaten). Westwards, the tunnel would connect to the existing line to Düren, a possible branch to Stolberg, and to Kornelimünster, using part of an old rail alignment.

The topography and geology of Aachen, and the historic buildings in the centre, would make this a difficult project. However, with a city population of 258 000, and 565 000 in the new Städteregion Aachen, the urban area is large enough to justify its scale.

Click to enlarge…

aachen-core

The tunnel would start at a new station on the east side of the marshalling yard, replacing the existing Aachen-West station. It would be accessed from a new footbridge (or road bridge) from Mies-van-der-Rohe-Strasse to Kühlwetterstrasse. The former marshaling yard here will be redeveloped in the coming years, as part of the Aachen Campus plan – a major expansion of the RWTH (Aachen Technical University). The plans do not include an upgrade of the rail line, but they are not incompatible with a new station. The Vaals branch would not pass through this station, but would join the new line just south of it.

The tunnel in the central area would have three stations. A station at the northern edge of the historic centre would also serve the original RWTH complex. The most central station would be located near the crossing Franzstrasse / Kapuzinergraben. Alongside Aachen Hauptbahnhof would be an underground station, approximately under the Römerstrasse.

gbf-west….central-aachen

The line would run under the Oppenhoff Allee, to near the existing station at Rothe Erde. Although Oppenhoff Allee is broad, the streets at both ends are not, and tunneling under buildings is unavoidable. East of Rothe Erde station, the tunnel would connect to the existing line toward Düren. Two new branches are also possible from there.

One is a direct route (south of Eilendorf) to Stolberg. The present euregiobahn trains to Stolberg-Altstadt must reverse at Stolberg Hauptbahnhof (which despite the name is not near the town centre). At first the line would follow the old Vennbahn alignment toward Brand, and then turn west to Stolberg. The line would cross the Inde valley on a viaduct, and approach Stolberg in tunnel – the town developed in a narrow valley. The line would terminate at either Unterstolberg, near the Town Hall, or further south, near the historical core (Altstadt). The 5 km of new alignment crosses open ground: that makes construction easier, but it would serve no housing between Eilendorf and Stolberg.

stolberg-line

The other branch would run via Brand, and terminate at the old Vennbahn station in Kornelimünster. The geographically simplest alignment (white dotted line) is in tunnel under the old main road through Brand (Trierer Strasse). The alignment along the Triererstrasse is difficult: the road climbs about 80 m, from Rothe Erde station to Brand. Nevertheless, the centres of the former settlements lie along the road: the easier-graded alignment of the old railway avoided them. An alternative alignment using part of the old line is shown in blue. It would have easier gradients, and is easier to build, but is at the edge of the built-up areas (Forst, Krummerück).

trierer-brand

After Brand, the Triererstrasse drops sharply, to cross a valley between Brand and Kornelimünster. If the new line runs east of the road here, a viaduct of 15 to 20 m height would be needed. The old alignment into Kornelimünster is intact, and in use as a cycle path: the station is in use as a restaurant.

brand-korneli

The proposed branch to Vaals would terminate at the edge of Vaals itself, at right angles to the main road. The line from Aaachen would use the existing lower ground alongside the Mies-van-der-Rohe-Strasse, turning to the west. It would enter a tunnel at a new station, at the crossing of the Mies-van-der-Rohe Strasse and Halifaxstrasse. It would then cross the Aachen ring road (Pariser Ring) on a bridge, and enter an underground station directly in front of the Klinikum (academic hospital of Aachen RWTH university). Beyond the car parks here are open fields: the line would drop about 20 metres in tunnel (turning south-west), then cross the stream (Selzerbeek / Senserbach), and then run parallel to the Grensstraat / Grenzstrasse. The station would be approximately on the site of the old Customs building, 100 m from the centre of Vaals.

halifax-line

The university has a project for a new link between its campus zones, the CampusBahn project. It was originally proposed as a people-mover, but has been scaled down to an isolated tram line. It would also terminate at right angles to the Vaalser Strasse, but further east.

Extension of a Vaals branch, to join the existing alignment to Maastricht would be difficult: see the propsed alignment for a Gulpen – Vaals – Aachen link. Apart from Vaals and Gulpen, the intermediate villages (Lemiers, Nijswiller, Wahlwiller) are small. Reactivation of the old line Richterich-Simpelveld-Valkenburg-Maastricht would probably be easier. In combination with a high-speed line Maastricht – Aachen, that would provide a comprehensive service between the two cities.

aachen-sbahn

The city-centre tunnel would also be used by trains from…

  • a new Sittard-Heerlen-Aachen line
  • Heerlen and Kerkrade via a new line Kerkrade-Kohlscheid
  • the existing line via Stolberg Hauptbahnhof to Düren, the terminus of the Köln S-Bahn line S12. Connecting to that line would create operational problems, the line is already 105 km long. The best option is an end-to-end terminus of the two S-Bahn systems, at Düren.
Urban-regional metro Aachen