In the 1960s, plans for converting the tram system to an underground rapid transit system were created, and the new tram sections to the Tynnered, Angered, Bergsjön and Länsmansgården suburbs were built free from level crossings and partly in tunnels to make a future conversion to underground standards easier. However, after further investigation, it was concluded that it would be too expensive to dig the necessary tunnels under the city centre, as the foundation of the city is partially made up of clay.