The twin-bore Bözberg Tunnel built for the N3 national highway swings its way from the Bözhalde underneath the SBB station of Schinznach Dorf in a long double S form across to the SBB station of Effingen in the upper reaches of the Frick Valley. The tunnel reaches its highest point at the Nordportal, which also marks the culmination of the entire N3 section between Basel and the Birrfeld.

To this end, a Single Shield TBM with a diameter 11,800mm started its advance on May 2, 1990. The S-56 is the first large diameter by Herrenknecht of this type of machine. And it proved to be desigend to the point right away: It bored some twelve meters on a daily basis. The 6,400-meter-long tunnel was excavated within a three-year span.