The reduction in journey times for long distance passenger trains between Freiburg and Basel initially amounts to two minutes.

[13] A three kilometre-long above-ground section connects the northern portal with the main line at the station of Schliengen (km 243).

The tunnel mostly passes through the soft strata of the foothills on the edge of the Upper Rhine Plain, which have been subjected to different degrees of weathering.

An exception is an approximately 800 m-long section at the southern half of the route that was drilled mainly through a form of Jurassic corallian limestone called Massenkalk.

[15] The original double-track line presented an obstacle to high-speed long-distance passenger transport because it followed the western edge of a steep ridge called the Isteiner Klotz and can only be operated at comparatively low speed due to the numerous curves in this area.

In 1979, the director of the Karlsruhe division of the Deutsche Bundesbahn, Zimmermann suggested an upgraded line between Bad Bellingen and Istein with three new tunnels for speeds of 160 to 200 km/h.

The Katzenberg tunnel option that was ultimately built was developed between 1977 and 1981 by the local engineer Albert Schmidt and his staff at their own expense.

[20] The planning approval procedure for the Schliengen–Basel section, to which the tunnel belongs, was conducted by the council of the Freiburg region from 1987 and compared the Katzenberg and the Rhine foreland options with each other.

[19][21] The Katzenberg option was identified as the most environmentally friendly and economical solution according to information supplied by Deutsche Bahn.

These plans were dropped in 1998 due to budget constraints; this was estimated to save about ten million marks.

[16] In response to the changing specifications of the Federal Railway Authority (Eisenbahn-Bundesamt) for fire and disaster control, two single-track tunnels were now planned.

[25] Due to changes in the Deutsche Bahn regulations and as a result of experience, the bores also could not be built with a drainage channel but were designed to cope with an expected water pressure equivalent to a water column of up to 90 m. This led to the adoption of a circular profile as an economic solution, which made the use of tunnelling machines possible.

[22] The neighbouring municipalities initiated legal action against the planning decision; this included a demand that the line in Bad Bellingen be moved to the east.

The contract for the construction of the tunnel, was finally awarded after several rounds of negotiations on 31 July 2003[22] to a consortium called ARGE Katzenbergtunnel.

Other important participants were the companies of Marti Tunnelbau AG (Bern, Switzerland) and Jäger Bau GmbH (Schruns, Austria).

[1] Due to the water pressure, the circular cross-section created by the TBM was the optimum shape for a tunnel.

[1] Upon completion of the plan approval process for this section in November 2002, work began with the building of an access road to the site of the north portal in December 2002.

[28] With the establishment of site equipment and the development of necessary infrastructure, construction work began at the south portal in November 2003.

Where the tunnel passes under the residential area of the town of Bad Bellingen the ground is unstable with the upper layer of soil moving downhill.

This is intended to prevent air pressure fluctuations from exceeding two-thirds of the level of conventional rail tunnels.

[35] From February 2005 onwards, a 2.5 km-long conveyor belt system was built to transport material to the Kapf quarry between 6 AM and 10 PM.

[1] Up to 168 full rings could be prepared per week in a 24-hour operation in the segment production plant that had been erected at the south portal.

[40] After preparation of the slab and track, the catenary, the control and safety systems and rescue technical equipment were installed.

Finally the interior of the connecting structures were fitted with doors, emergency power supply, communication systems and fire-fighting equipment.

[1] In December 2009, Balfour Beatty Rail began with the survey work for the construction of the overhead line and the first holes were made in January 2010.

[43] At 8:00 AM on 7 September, a Stadler FLIRT multiple unit operated by SBB GmbH (Swiss Federal Railways Germany) departed as the first electric train to pass through the tunnel at 155 km/h, also making video recordings.

[6] The first official operations through the tunnel took place shortly after 2:30 PM from the north to the south portal with parallel trips of ICE-T multiple unit set 1502 ("Karlsruhe") and a freight train hauled by a Siemens EuroSprinter locomotive.

[47] The High-speed rail services and much of the freight traffic travelling on this section of the Rhine Valley line run through the tunnel.

The federal and state governments and Deutsche Bahn have agreed to an optimisation of the interconnection points (in particular via grade-separated connections) to avoid forecast traffic congestion in 2025.

DB Netz announced in November 2012 that it would adjust the route prices from the end of 2014 so that freight trains would have no incentive to use the old line.