Stadtbahn (literally in German: city railway), or Premetro, is a tramway or light railway which includes segments built to rapid transit standards, usually as part of a process of conversion to a metro railway, mainly by the building of tunnels in the central city area.
Mostly, the systems were implemented in the 1960s and 1970s with the long-term goal of establishing a full-scale metro system. By the 1980s, however, virtually all cities had abandoned these plans due to the excessive costs associated with converting the tramways, and most Stadtbahn systems now are a mixture of tramway-like operations in suburban and peripheral areas, and a more metro-like mode of operation, featuring underground stations, in the city centres.
The Wiener Stadtbahn (Vienna) was in the beginning a system of heavy rail lines circling the City, free of level crossings, that was operated with steam powered trains. After World War I the Wiental, Donaukanal and Gürtel lines were converted into an electricity powered light rail system with tram-like two-axle cars (which, on 18G line, until 1945 actually switched into the tram network at Gumpendorfer Strasse station). In the 1970s to 1990s the infrastructure was updated, and the lines were partially relocated. It is now part of the U-Bahn services 'U4' and 'U6'. The Vorortelinie line remained heavy rail and is now part of the Vienna S-Bahn services.
Since the 1960s the term "Stadtbahn" has become identified with a second, and now dominant, meaning.
Post-World War II transport policies in West German cities aimed for a separation of public and private transport. The conflicts that arose between increasing car usage and the existing tramway systems led to the so-called 'second level' concept for future light rail schemes. This concept focused on the grade separation — i.e., elevation and/or tunneling — of tram lines.
Munich and Nuremberg finally decided to start building pure, full-scale U-Bahn (metro) systems. Berlin and Hamburg planned expansions of their existing U-Bahn networks, while most West German cities decided to upgrade their tramway networks step by step, linking new 'second level' infrastructure to existing sections. While some cities regarded this solution as an interim step that would lead to a fully separated U-Bahn (metro) network independent of other forms of transport, others planned for a lesser degree of separation, one that would accommodate additional tram-like sections in the long run. For both the interim and the long-term based concepts, the following terms came into use: "U-Straßenbahn" or "Untergrund-Straßenbahn" (underground tramway, abbreviated as "U-Strab") , "Schnellstraßenbahn" (rapid tramway) and finally "Stadtbahn". (In French-speaking countries, these concepts were also known as "pre-metro", stressing their interim nature.)
Some operators and cities decided to identify the term Stadtbahn with the eventual goal of installing an U-Bahn so that both the original U-Bahn logo (e.g. Frankfurt, Cologne, Hannover) and the derived U-Stadtbahn logos (e.g. North Rhine-Westphalia, Stuttgart; see example above) can be seen in use for marking station entries and stops. Even the numbering scheme for Stadtbahn services was prefixed with a 'U', except in Cologne, Bielefeld, and Hannover.
It is important to differentiate between the Stadtbahn and the S-Bahn. "S-Bahn" nowadays stands for "Stadtschnellbahn." In contrast to the (new) Stadtbahn systems as detailed in this paragraph, S-Bahn systems are fast city and mainly suburban trains that also have urban metro-like service but run on mainline railway tracks (often but not always sharing the tracks with long distance trains) and use mainline (heavy rail) grade rolling stock. Furthermore, almost all S-Bahn systems (with one exception in Karlsruhe) are run by the Deutsche Bahn AG. They also differ in legal status: S-Bahn systems are governed under the heavy rail rules of the Eisenbahn-Bau- und Betriebsordnung (the federal regulations on building and operation mainline railways), while Stadtbahn systems are tramways by law, governed under the regulations of BOStrab (the federal regulations on building and operationg tramways).
By the 1980s, the conventional tramways had been seen by decision-makers as overloaded systems for almost two decades. However, public attention focused on them at this time for two reasons.
The Stadtbahn cities' second level plans faced unexpected complications in the form of lengthy construction work, budgetary problems for tunnel projects, and protests against elevated sections. At the same time, the smaller cities which had not started Stadtbahn plans reassessed their options in relation to their existing tram systems.
The "Stadtbahn" term has now come to have the vague meaning of 'modern tramway' or 'modernized tramway'. It has become impossible to differentiate between Straßenbahn (trams) and Stadtbahn (light rail).
East German cities had no 1960s-style Stadtbahn plans in place, and the fleet as well as infrastructure were in need of massive investment and improvement. After the reunification of Germany in 1990, the use of the "Stadtbahn" term became popular in the former East Germany, as well, and is seen is cities such as Erfurt and Dresden.
"Stadtbahn" in this wider meaning is thus not a clearly defined concept, but a vague one linked to a set of attributes, much in the same way that "Straßenbahn" (tram) is linked to very different, sometimes mutually incompatible attributes. A system that is called "Stadtbahn" today may not have all of the Stadtbahn attributes: barrier-free access, higher cruising speed than tramways, doors on both sides of the train, driver's cabs on both ends, higher operating voltage, wider cars with comfortable seats, and so on.
In 1992 the public transport operator in Karlsruhe started a new service, using both heavy and light rail infrastructure, to link the wider region (suburbs, villages) to the city. The vehicles used for this purpose — and this was the innovation — are designed to comply with both sets of technical specifications: those for the (federal) heavy railway and those for light rail (communal tramways). Such vehicles are called Dual-System Light Rail Vehicles.
Again, the meaning of Stadtbahn was enlarged to encompass this new type of "tram-train" service. In other regions, stimulated by the Karlsruhe example and planning to copy it, other terms for it are in use as well: Stadt-Umland-Bahn (city-to-region railway, e.g. Erlangen), Regional-Stadtbahn (regional light rail, e.g. Braunschweig).
Today, Straßenbahn (tram) and Stadtbahn in the Karlsruhe region are differentiated more by the nature of their city-border crossings only, and not by the technical dimension (Dual-System Light Rail Vehicles). Only those services that extend into the suburbs are called Stadtbahn. They are represented by the 'S' logo that is used for 'S-Bahn' (Stadtschnellbahn) in the rest of Germany and therefore partially conflict with it, as it has acquired a second meaning in Karlsruhe.
As part of the redevelopment of their main city stations, national railway company Deutsche Bahn adopted a new logo to indicate Straßenbahn (tram) connections: a square containing the word 'Tram'. Although the design is the same nationwide, the actual colour used can vary from city to city to match local public transport operators' own systems of colour coding. The logo is part of the 'S logo scheme' which was initially developed by Berlin public transport operator BVG; this scheme, based on the already established logos for urban metro ('U', for U-Bahn) and suburban metro ('S', for S-Bahn) also covers bus ('Bus') and ferry ('F', for Fähre) operations.
As the new logos became part of the information systems of more and more main railway stations, an increasing number of cities and public transport operators came to accept and adopt the scheme themselves. As far as the Stadtbahn terminology problem is concerned, however, the scheme serves only to add further confusion to the matter, since there is no nationwide logo for Stadtbahn services as such. The result appears to be a contraction in the use of the term Stadtbahn itself, especially in those cities where it has been used in its wider 1980s 'light-rail system' meaning.
In cities where Stadtbahn refers rather to the 1960s 'pre-metro' meaning, both the 'U' (for U-Bahn) and the 'Tram' logo are used on city maps (to indicate the location of stops) and on railway station signage (to indicate connections). The 'U' Logo is normally used both where stops or stations actually are underground and where they serve 'second-level' pre-metro type lines. In those cities which prefix all their Stadtbahn line numbers with a 'U' (e.g. Stuttgart), the 'U' logo can be found even at stops on services which are not 'second-level' at all, but essentially 'classic' tram lines.
Up to this point, our description of the Stadtbahn term has been about the intended use (what decision-makers and marketers intended). The public perception (politicians, customers/passengers) has been different.
Mainly, the Stadtbahn term is much more widely used and well known among decision-makers and marketers.
Where it became clearly identified with investment and urban redevelopment, the term had some success in reaching the public, depending on whether it has still been used alongside other terms like 'U-Bahn', 'Straßenbahn' or 'U-Straßenbahn'.
Only little success in the meaning of getting widely used - instead of 'Straßenbahn' (tram) - was dedicated to most of the systems with 1980s concept of Stadtbahn. This evolution was further driven by the introduction of the 'Tram' logo and the absence of a nationwide standardized Stadtbahn Logo (since for those systems without underground sections, the partially standardized 'U-Stadtbahn' Logo would not be appropriate).
In most of the cities with systems that include underground, ground-level and sometimes elevated line sections, all three terms are in wide use for the whole system or to the corresponding sections: 'Straßenbahn' (tram), 'U-Bahn' (metro), Stadtbahn.
Although a precise legal definition of Stadtbahn was planned in the 1970s, there is currently no such definition. By law, the 'BOStrab' regulate all Stadtbahn systems (and Subways) as 'Straßenbahn' (tram) systems, as long as they are light rail rather than heavy rail.