Sieg Railway
The route runs on the Cologne–Aachen line (opened by the Rhenish Railway Company between Cologne and Horrem in three stages between 1839 and 1841), the East Rhine Railway (opened to Troisdorf by the Rhenish Railway in 1870, with an extension to Cologne opened in 1874) and the Sieg Railway (opened by the Cologne-Minden Railway Company between 1859 and 1862). The eastern section of the S 12 service from Au (Sieg) to Köln-Nippes was opened on 2 June 1991. It was extended to Düren on 13 June 2004, dropping Köln-Nippes. It was cut back to Horrem in December 2015.