S13 (Rhine-Ruhr S-Bahn)  Line S 13 is a S-Bahn line of the Rhine-Ruhr network. It is operated by DB Regio with class 423 electric multiple units. At peak times, the S13 services begin or end at Düren and run via Cologne to Troisdorf. In the off peak, half the S13 trains begin or end at Sindorf. It runs with line S12 for most of its route, splitting from it only to run through Cologne/Bonn Airport. On working days, two services operate every hour (20 or 40 minutes apart) and together with an hourly service on line S19, services operate at 20-minute intervals. Between the peaks the S12, S13 and S19 services provide a service every 10 minutes on the central section between Köln-Ehrenfeld and Köln-Trimbornstraße. It operates every 60 minutes on Saturdays, Sundays and public holidays between Düren and Troisdorf; lines S13 and S19 jointly provide a service every 30 minutes. The S12, S13 and S19 services provide a service every 15 minutes on the central section between Köln-Ehrenfeld and Köln-Trimbornstraße. 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 on 13 June 2004. It is proposed to extend the line to Bonn-Oberkassel.