During the 1980s, the city decided to connect the four suburban lines west of the city center with the Oslo Metro. The Sognsvann Line was selected as the first line to be upgraded, so the two systems would become compatible. The line was upgraded to metro standard by replacing the overhead wire with a third-rail power supply and installing automatic train protection. All the stations were rebuilt, with platforms lengthened from fitting two-car to fitting four-car trains, and the platform height increased. The third rail required all level crossings to be removed, resulting in the line being rebuilt several places to allow the road to underpass or overpass. The light rail permitted passengers to cross the lines at the stations, but this was made impossible with metro standard. Because of this, underpasses or overpasses were built at the stations.