Built and operated by the Norwegian State Railways, the non-electrified, standard gauge line passes through the municipalities of Kongsberg, Flesberg, Rollag and Nore og Uvdal.

The line runs past four stops, Spiten, Pikerfoss, Gleda and Herbru, before reaching a branch to Svene Gravel Pit, 3.48 kilometers (2.16 mi) from Kongsberg.

The line continues past the halts Ramsrud, Svene, Furuly and Toresplassen before reaching Lampeland Station, 10.50 kilometers (6.52 mi) from Kongsberg.

The line then passes over Lyngdalselva on a 27-meter (89 ft) bridge and continues past the stops Fløtterud, Ruud, Vangestad and Eie before reaching the branch to the sawmill Numedal Bruk, 29.69 kilometers (18.45 mi) from Kongsberg, which is located just south of Flesberg Station.

[2] The line continues past the stops Bjørnsrud, Bakkerud and Fossan before reaching the 228-meter (748 ft) Helle Tunnel and then Djupdal Station 40.63 kilometers (25.25 mi) after Kongsberg.

After passing through the halt Kjome, the line reaches Rollag Station, which is 46.80 kilometers (29.08 mi) from Kongsberg.

[3] The line continues past the stops Tråen, Rollag kirke, Bråten, Sjorsåte, over the 65-meter (213 ft) Bruhaug Bridge, past the stops Laugi, Vamre, Risteigen and then passes over the river Veggli elv on a 30-meter-long (98 ft) bridge.

At 60.81 kilometers (37.79 mi) after Kongsberg the line reaches Veggli Station, before continuing past the stops Tveitkåsa, Kjerre, Fossebrekke and then through two tunnels, Gjeiteryggen I and Gjeiteryggen II, which are 572 meters (1,877 ft) and 246 meters (807 ft) long, respectively.

The line then passes over Uvdalselva on a 35-meter (115 ft) combined road and rail bridge, before reaching Rødberg, 92.84 kilometers (57.69 mi) from Kongsberg.

A minority of the parliamentarians instead wanted the line to be built with narrow gauge to reduce construction costs.

190,000 cubic meters (6,700,000 cu ft) of ballast stone were used, most of it from the gravel pits at Bevergrenda, Guribråten and Stevningsmogen, Tjuvhaugen and Skarpsmoen.

Five of the station buildings, at Vangestad, Flesberg, Djupdal, Tråen and Kravikfjord, were workmen's sheds which had been placed on a foundation.

During World War II, the line was again entirely hauled by steam locomotives and the service was reduced considerably.

[11] Because the conductors and engineers often knew where the locals lived or were headed, trains would make non-scheduled stops to disembark passengers to allow them a shorter walk.

[8] In the 1960s, the number of round trips was reduced to three per day, allowing the whole service to be operated with a single unit.

[13] For a short period during the 1980s, there were also school trains, but as this forced NSB to operate two multiple units on the line, it proved too expensive and was soon afterwards again provided by bus.

The last passenger train operated on 31 December 1988 and the line north of Rollag was officially closed on 1 January 1989.