In November 1970, the Dovre Line was electrified, and the last steam locomotives were retired. A long-term plan to electrify half the lines was finished, and for two decades, NSB's operations were very stable with no major investments to infrastructure or closing of lines. NSB had slightly less diesel locomotives than they needed, but plans to order additional Di 3 was never fulfilled. In 1981, NSB took delivery of five Di 4 to supplement the older units. They were mainly used on the Nordland Line, and Di 3 units were predominantly used on the other lines, although they continued to operate som trains on the Nordland Line. On 1 April 1987, a Di 3 612 caught on fire; the damage was small enough that it could have been repaired, but NSB instead decided to put aside the unit. At the time NSB planned to order additional Di 4, but these plans were put on hold. In 1988, the Valdres Line was closed; this was the only time a line with Di 3 in regular service was closed.