The line was opened in 1906 as part of the private "København-Slangerup Jernbane" which went to Slangerup, about two thirds from Farum to Frederikssund. Its terminus in Copenhagen was København L, close to present day Nørrebro station on the S-train ring line - the station building of this station still stands. This was quite a bit from the city center, but the station was supposed to be temporary until the exact routing of the various new railways near Copenhagen that were in planning around the turn of the century had been finalized.