S1 (Rhine-Ruhr S-Bahn) Services ran via Düsseldorf Airport Terminal station from 24 May 1998 to 28 May 2000. Services were extended from Düsseldorf to Solingen on 13 December 2009, replacing part of the former line S 7 service. S1 (Rhine-Ruhr S-Bahn) Line S1 is a S-Bahn line on the Rhine-Ruhr network. It is operated by DB Regio. It runs from Dortmund west over Essen to Duisburg. From there it travels south to Düsseldorf and Hilden before continuing to Solingen. It is operated at 20 minute intervals, using coupled sets of class 422 four-car electrical multiple units. Line S 1 runs over lines built
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