During the building of the first tramline in Essen in 1893, planning began on a partially underground railway, which was not realised until decades after the Second World War. The first preliminary line of the current Stadtbahn emerged in the early 1960s and were laid partly as tram tracks on the median strip of the
Ruhrschnellweg ("Ruhr Expressway"), which is exactly where the modern line U18 runs. In this case, an underground Stadtbahn (
U-Stadtbahn) was not initially planned. Construction work on the tram line in the Ruhr Expressway was carried out simultaneously with the upgrade of the Ruhr Expressway itself, since the latter up to that time had only three lanes and flat junctions and had insufficient capacity because of the large increase in traffic. Following the upgrade of other forms of public transport, the possibility of some form of public transport on the Ruhr Expressway were considered, including express buses on a separate bus lane. Ultimately, however, an option based around a rapid tramway gained favour. Thus a line was built on parts of today's Essen–Mülheim route, which was initially connected by temporary exit ramps with the rest of the tram network. The plans for a tunnel under the centre of Essen replacing an above-ground tram line began in 1961. Again, there were considerations of relieving the above-ground tramway and congestion in the quite small Essen inner city (about ), which suffered from increasing traffic. The initial solutions ranged similarly from the retention of the surface tramway with the creation of a new centralised node, up to the creation of a pure
U-Bahn (metro) system as in
Berlin and
Hamburg. For various reasons, however, it was agreed to build an underground tramway with the possibility of future upgrade to a full U-Bahn. The idea of building a pure U-Bahn system at once was considered, but discarded due to the need to handle the existing passenger flows linking the tramway systems of the neighbouring cities of the Ruhr. Soon after that actual planning started on the tunnels in the city centre. The planning was carried out simultaneously on the construction of a highway tunnel for the Ruhr Expressway underneath the inner city. In the end, the so-called
Y-Lösung ("Y solution") was adopted under which the
Essen Hauptbahnhof Stadtbahn station became a central, four-track junction station serving all lines, which a branch in the north to the northeast and the northwest. The first construction project was the establishment of the shell of Planckstraße station in 1964, which was later used for the connection to the existing above-ground tram line to Margarethenhoehe. The first section of the underground tram line to go into operation, however, was a -long urban tunnel section through Saalbau station, opened on 5 October 1967. This was also the first part of the entire underground tram (
U-Straßenbahn) network of the Rhine-Ruhr region, since Saalbau station was also the first underground railway station in North Rhine-Westphalia. The next phase of construction was the building of the continuous Stadtbahn line from Essen to Mülheim along the Ruhr Expressway, which, as has already been mentioned, was partly built in the 1960s. This route was considered a "model line" for the other Stadtbahn construction projects. On 28 May 1977, the opening of a nearly eight kilometre-long, continuous connection between Mülheim-Heißen and the Essen inner city took place, including the underground stations of Heißen Kirche in Mülheim city and the metro stations of Bismarckplatz, Essen Hauptbahnhof and Wiener Platz (now Hirschlandplatz) in Essen. This was the first Stadtbahn line of the network that was completely independent of the tram network to be opened. Porscheplatz (now called Rathaus Essen) Stadtbahn station was also put into operation on 28 May 1977; it was (and still is) operated by trams. The commissioning of the remaining five underground stations in Mülheim followed on 3 November 1979. In 1981, the route of line U17 to Margarethenhoehe was put into operation. This included Planckstraße station, which had been built as a shell in the 1960s along with its associated ramp. The surface stations initially had low platforms located on the outside of the tracks, which were raised in 2002 and relocated onto islands between the tracks. At the same time, the two underground stations of Berliner Platz and Universität Essen (
University) were opened; both are also stations on line U18 and Universität Essen is a station on line U17. The next construction phase now included for the first time the construction of an underground section on the outskirts of Essen, namely the building of the so-called southern line (
Südstrecke) from the existing Saalbau station towards Messe/Gruga and Bredeney. This line was equipped with
dual gauge track with three rails for both Stadtbahn and tramway operations to Martinstraße station; south of that station the lines branch to form pairs of
metre gauge and
standard gauge track. This included four underground Stadtbahn stations for line U11 and, south of the junction, an underground tram station at Florastraße. Services started in 1986. The last major phase of construction to date was the northern extension, carried out in two stages. In 1998, the tunnel was finished from Universität Essen station to
Altenessen station. Three years later, the section was opened to Karlsplatz and up the ramp to the surface station of II. Schichtstraße. U11 services ended at Karlsplatz, while U17 services continue to
Gelsenkirchen, the above ground section north of Karlsplatz was upgraded up to 2001 on the route on an earlier metre-gauge tram line for standard gauge Stadtbahn operations. The Gelsenkirchen section of line U17 ended from 2001 to 2004 at Fischerstraße. Two extra stations in Gelsenkirchen, Schloss Horst and Buerer Straße, were taken into operation in 2004. From January 2010, line U11 operated to Gelsenkirchen Buerer Straße, replacing line U17, which now ran only as far as Berliner Platz. Line U18 was called a "shopping line" and continued to Karlsplatz station. Since September 2011, line U11 continues to Gelsenkirchen Buerer Straße and line U17 has replaced line U18 to Karlsplatz. Line U18 has run since September 2011 between Mülheim Hauptbahnhof and Berliner Platz in Essen. == Lines and stations ==