Variations investigated included a line through Gelterkinden and from there to Tecknau or Anwil and then through a tunnel under the Schafmatt Pass to Aarau.

The clear winner of these variants was the Läufelfingen line, because of its shorter tunnel and its slightly lower estimated construction cost.

The construction of the summit tunnel in 1853 by the Schweizerische Centralbahn (SCB) was a big challenge, because never before had a mountain range been penetrated in Switzerland.

The English contractor Thomas Brassey decided to drive the tunnel from five points—both ends and from three perpendicular shafts from the surface of the mountain to the axis of the tunnel—in order to accelerate the project.

Horses, men from many countries and many children were working under great danger in the tunnels and had to breathe stifling smoke and dust.

On 28 May 1857, a fire spread from a forge at the top of one of the shafts into the tunnel and set alight its lining boards and their supporting beams.

Nevertheless rescue parties pressed on, but they had to be called off when 11 rescuers died from carbon monoxide poisoning and many others lost consciousness.

In 2006 was the "Läufelfingerli" was again seriously threatened by replacement with buses, but this was rejected by the parliament of the canton of Basel-Country on 16 November and funding was secured for rail services (as route S9 of Regio S-Bahn Basel) until 2009.

The supporters of replacement of buses pointed out that cost recovery on the line was about 19 percent (against 63 percent in the S3 service on the Hauenstein base tunnel line or 70 to 80 percent for trams in suburbs of Basel in Basel-Country) and that the limited resources available for public transport could be more effectively used for the promotion of rail transport in the more densely populated urban areas, while buses would be more suitable for serving the villages in the Homburger valley served by the line with its rather large distances between stations.

On the other hand, the advocates of maintaining rail services pointed out that buses never offered an equivalent replacement for trains (for example in terms of comfort and punctuality).

It was expensive to carry out these complicated operations and to provide and maintain facilities for attaching and detaching locomotives at Sissach and Läufelfingen.

When the Swiss Federal Railways acquired the network of the Schweizerische Centralbahn in 1901 it sought for an alternative route from Olten.

Capacity was increased as part of Rail 2000 by the opening of a bypass of the bottleneck at Pratteln with an over 5 km-long Adler Tunnel between Liestal and Muttenz in December 2000.