 In the 1980s , the stations on the Sognsvann Line were rebuilt . The platforms were 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 <unk> was therefore constructed at Berg station . The station was also redesigned in concrete with steel columns and wooden sheds designed by architect Arne <unk> . 
