Rhine-Ruhr S-Bahn Rhine-Ruhr S-Bahn The Rhine-Ruhr S-Bahn () is a polycentric and electrically driven S-train network covering the Rhine-Ruhr Metropolitan Region in the German federal state of North Rhine-Westphalia. This includes most of the Ruhr (and cities such as Dortmund, Duisburg and Essen), the Berg cities of Wuppertal and Solingen and parts of the Rhineland (with cities such as Cologne and Düsseldorf). The easternmost city within the S-Bahn Rhine-Ruhr network is Unna, the westernmost city served is Mönchengladbach. The S-Bahn operates in the areas of the Verkehrsverbund Rhein-Ruhr (VRR) and Verkehrsverbund Rhein-Sieg (VRS) tariff associations, touching areas of Aachener Verkehrsverbund at Düren
Ruhr breaks between the individual city boroughs. Thus the Ruhr is described as a polycentric urban area, which shares a similar history of urban and economic development. Because of its history, the Ruhr is structured differently from monocentric urban regions such as Berlin and London, which developed through the rapid merger of smaller towns and villages with a growing central city. Instead, the individual city boroughs and urban districts of the Ruhr grew independently of one another during the Industrial Revolution. The population density of the central Ruhr is about 2,100 inhabitants per square kilometre (about 5,400 per square mile)—low compared