S12 (Rhine-Ruhr S-Bahn)

It is operated by DB Regio using class 423 electric multiple units.

With over 105 kilometres (65 mi), it is the second longest S-Bahn line in North Rhine-Westphalia, after S9.

The S19 also operates hourly between Au (Sieg) and Hennef, so there is a 30 minute clock.

On Sundays and public holidays the S12 operates every 30 minutes between Horrem and Au (Sieg).

The eastern section of the S 12 service from Au (Sieg) to Köln-Nippes was opened on 2 June 1991.