Steam locomotives remained in regular use on freight trains until 1965 and were used sporadically until 1969. To allow for the heavier Di 3 diesel locomotives, the southern part of the line needed to be upgraded to the same standard as the northern. Sturdier 30 kilogram per meter (60 lb/yd) tracks were laid on top of an improved layer of ballast, allowing the line speed to increase from . The work allowed NSB to capture a significant amount of the lumber transport after the forest industry terminated its log floating operations in the late 1960s.