v ann ▁station . ▁The ▁line ▁was ▁double - track ed ▁from ▁Major st uen ▁to ▁K ors vol l , ▁and ▁single - track ed ▁from ▁there ▁to ▁S og ns v ann . ▁In ▁ 1 9 3 9 , ▁the ▁section ▁K ors vol l – S og ns v ann ▁was ▁upgrad ed ▁to ▁double ▁tracks , ▁and ▁the ▁station ▁K ors vol l ▁had ▁its ▁name ▁changed ▁to ▁ Ø st horn . ▁The ▁name ▁" Ø st horn " ▁ow es ▁its ▁orig ins ▁to ▁a ▁c rag ▁by ▁the ▁same ▁name ▁that ▁was ▁demol ished ▁during ▁the ▁construction ▁of ▁the ▁S og ns v ann ▁Line . ▁The ▁station ▁is ▁now ▁position ed ▁inside ▁the ▁remains ▁of ▁the ▁c rag , ▁with ▁a ▁metal ▁nest ▁put ▁up ▁to ▁prevent ▁any ▁cr umb ling ▁of ▁the ▁surrounding ▁c rag . ▁▁ Ø st horn ▁was ▁part ▁of ▁Hol men kol ban en ' s ▁operating ▁network ▁until ▁ 1 9 7 5 , ▁when ▁the ▁municipality ▁of ▁Os lo ▁bought ▁all ▁the ▁company ' s ▁stock . ▁In ▁ 1 9 9 3 , ▁the ▁stations ▁on ▁the ▁S og ns v ann ▁Line ▁were ▁upgrad ed ▁to ▁met ro ▁standard , ▁which ▁involves ▁a ▁height ening ▁and ▁length ening ▁of ▁the ▁platforms , ▁and ▁installation ▁of ▁third ▁rail ▁power ▁supply ▁and ▁a ▁new ▁signal ing ▁system . ▁During ▁the ▁upgrade , ▁T å sen ▁station ▁was ▁moved ▁ ▁further ▁north , ▁and ▁Nord berg ▁station ▁was