Line S 13 is a S-Bahn line of the Rhine-Ruhr network. It is operated by DB Regio. The S13 runs from Horrem, at peak times, via Cologne to Troisdorf. Normal operation begins at Köln Hansaring. It runs with Line S 12 for most of its route, splitting from it only to run through Cologne/Bonn Airport. Services operate every 20 minutes on working days and every 30 minutes on Saturdays, Sundays and public holidays, using class 423 electric multiple units.
The route runs on the Cologne–Aachen line (opened by the Rhenish Railway Company between Cologne and Düren 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 Cologne Airport loop (opened in 2004) The western section of the S 13 service from Düren to Köln Messe/Deutz was opened on 15 December 2002. It was extended to Troisdorf in 13 June 2004, dropping Köln Messe/Deutz. It is proposed to extend the line to Bonn-Oberkassel, with construction possibly starting in 2012 and services starting at the end on 2016.