In the 1980s , the stations on the Sognsvann Line was rebuilt . The platforms was lengthened from fitting two @-@ car to fitting four @-@ car trains and the platform height was increased . The third rail made it impossible to cross the line at @-@ grade ; an underpass was therefore constructed at Berg station . The station was also redesigned in concrete with steel columns and wooden sheds designed by architect Arne Henriksen .