The final expansion took place in 1955. To test out the ridership for the Rosenborg Loop, a bus was rented to test drive the loop from Asbjørnsens gate, down Henrik Mathiesens gate, back along Stadsingeniør Dahls gate and Frestningsgata, before meeting up with the old track at Tyholtveien. The single track section from there to Gudes gate would then have to be rebuilt to double track. A proposal to run a single-tracked line onwards from Rosenborg to Buran, connecting onwards to the Lademoen Line, was discarded, as was a loop at Solhaugplatået. The Rosenborg Loop had originally been suggested by the Communist Party in 1946, and the loop would cost just short of NOK 1 million. There were some local protests from people at Øvre Rosenborg, since they would have a longer route into town than via Buran.