In 1858 the Schweizerische Centralbahn opened a line from Brugg to Olten, connecting to its Hauenstein line to Basel. At the same time the Zürich-Baden line (which by that time had been merged into the Schweizerische Nordostbahn) was extended to connect with the Centralbahn's line at Brugg. Construction of an alternative route, known as the Bötzbergbahn (BöB) began in 1870 and it was opened on 2 August 1875 through the Bözberg Pass from Pratteln to Brugg via the Frick valley and the 2,526-metre-long Bözberg Tunnel by a joint venture of the Centralbahn and the Nordostbahn. This line is 49 km long, about 8 kilometers shorter than the line via Olten. Trains on it used the Centralbahn between Basel and Pratteln and the Nordostbahn between Brugg and Zürich. The single-track line was built with a maximum grade of 1.4%.