After Immenstadt had been connected to the railway network by the Allgäu Railway in 1853, Sonthofen sought to be connected to the network by a branch line. The 8.33 km long Vizinalbahn was opened on 16 November 1873 and was operated by the Royal Bavarian State Railways. The new line branched off from Immenstadt station to the east, so trains coming from Kempten and running to Oberstdorf have to reverse in Kempten. The 13.38 km long line from Sonthofen to Oberstdorf was opened by the Lokalbahn AG company on 29 July 1888. It was classified as a secondary line. It shared the terminus in Sonthofen with the State Railways. The private LAG also took over operations on the existing Immenstadt–Sonthofen section. With the nationalisation of the LAG on 1 August 1938, the Deutsche Reichsbahn became responsible for the entire route, which was now administered by the Reichsbahndirektion Augsburg. The Deutsche Bundesbahn eventually replaced the old Sonthofen station with the current through station on the western outskirts on the route to Oberstdorf on 2 October 1949. With the construction of the connecting curve at the same time, the line was shortened time from 21.71 to 20.704 km. The construction of the new Sonthofer station commenced on 15 November 1937, but was delayed due to the war and was not recommenced until 30 August 1948. The old Sonthofen station building—it was located on Promenadestraße, opposite the junction with Schnitzerstraße—was demolished in 1962 as part of the redevelopment of Oberallgäuer Platz. The name of the street Am Alten Bahnhof there means "at the old station". Oberstdorf also had a separate Bahnbetriebswerk until 23 March 1951. It was then converted into a branch of Kempten locomotive depot.
Operations
The line is served every two hours by a Regional-Express service from Ulm to Oberstdorf and also every two hours by an alex service from Munich to Oberstdorf. The service is complemented by an hourly Regionalbahn service between Immenstadt and Oberstdorf and the IntercityAllgäu Express service from Hanover to Oberstdorf and back. This service runs from Ulm to Oberstdorf as a Regional-Express and can be used with regional tickets. Running in the opposite direction towards Hanover, however, the train runs along the whole length of the line as an Intercity and Intercity fares apply.
