The old Hauenstein line was inaugurated in 1858. The double track line linked Basel to the railway junction of Olten. The section Sissach - Läufelfingen - Olten is a quite steep (up to 27 per thousand) line, therefore a new base line was built via Tecknau, with the 8134 m long Hauenstein base tunnel. It was ready in 1916. After the opening of the Hauenstein base line, the old summit line lost its importance, and eventually it was reduced to single track in 1938. Since the 90's, the old line has been close to getting shut down several times. Nowadays, the Hauenstein summit line is part of the Regio S-Bahn Basel network, but the threat of closure is still present.  The S9 operates at a loss, the trains called "Läufelfingerli" by the locals are used only by a few passengers.

Regarding the passenger volume, it is not advantageous, that the trains circulate only between Olten and Sissach, therefore passengers to Basel have to change in Sissach. The hourly cadence also doesn't make the S9 attractive. On the S9 shuttles an  NPZ double unit, class RBDe 560, which means a lower comfort level after the FLIRT trainsets of the S3 running on the Hauensterin base line.

Still, the situation is not hopeless.  A company, the Modern Steam am Hauenstein GmbH presented a bold idea. They would like to operate this railway line with steam push-pull trains in place of the electric trainsets. According to their concept, the steam trains would attract many tourists, especially outside of rush hours, when the S9 runs nearly empty. The high comfort low floor trailers could be hauled by a modern, economic, low emission steam locomotive. The steam trains would take over the whole S-Bahn traffic from the electric trainsets.

The MSaH GmbH launched a two week test period between 26th September and 11th October 2009 to prove the project's feasibility. The daily 2-3 pairs of trains were hauled by the modern steam loco 52 8055 of DLM (Dampflokomotiv- und Maschinenfabrik AG). The test operation is not without precedent: on the occasion of the 150 year jubilee of this railway line in 2008 3000 tickets could be sold for the steam trains of Modern Steam during one single weekend, while the electric S9 operated free of charge.

Attention! The steam train runs again in 2010! From 31 July to 8 August four pairs of trains circulate on the Hauenstein line. More info on the website of Modern Steam am Hauenstein (see below).