Despite the town’s small population, the junction station is important for commuters from the districts of Altenkirchen, Neuwied and Westerwaldkreis for its connections towards Siegen, Cologne, Bonn, Düsseldorf and Aachen.

Au (Sieg) station has a commuter car park and a "bike and ride" cycle storage.

Until the introduction of the 2014/2015 timetable in December 2014, Au (Sieg) station was the terminus of two Regionalbahn lines.

In 2004, Vectus Verkehrsgesellschaft took over the operations of the Upper Westerwald Railway between Limburg (Lahn) and Au (Sieg).

On the main line (the Sieg Railway from Cologne to Siegen), it is served by the Rhein-Sieg-Express, running from Aachen via Cologne and Betzdorf to Siegen (RE 9), along with the S-Bahn S 12 services from Köln-Ehrenfeld (Horrem in the peak) and on week days by S19 services from Düren.