The Randsfjordbanen was Norway's fifth railway line, built to connect Drammen with the lake Randsfjorden via the Drammenselva valley. The 87 km line opened on 12 October 1868, with King Charles XV attending the celebration at Randsfjord station near Jevnaker.
The idea came as early as 1846, before any railways existed in Norway. Drammen wanted better transport links to the timber districts around Tyrifjorden and Randsfjorden. A canal was considered but rejected since it could only operate half the year. Railway director Carl Abraham Pihl surveyed the route in 1857 and parliament approved construction in 1863.
The line was built in stages. Drammen to Vikersund opened in September 1866, extended to Tyristrand in December 1867, and finally reached Hønefoss and Randsfjord station in October 1868. At Randsfjord, passengers could transfer to steamships for onward travel on the lake.
Like most Norwegian railways of the era, it was built with Pihl's cheaper 1,067 mm narrow gauge rather than standard gauge. This saved money but created problems as the network expanded. When the Bergensbanen was planned, parliament decided in 1898 to build it with standard gauge. The Randsfjordbanen was converted to 1,435 mm standard gauge in 1909 to connect with the new Bergen line.
Two branch lines were built from the Randsfjordbanen: the Kongsberg line from Hokksund in 1871, and the Krøderbanen from Vikersund in 1872. The Krøderbanen now operates as a heritage railway.
Electrification came in stages: Drammen to Hokksund in 1929, Hokksund to Hønefoss in 1959. Passenger services north of Hønefoss to Randsfjord ended on 26 May 1968, exactly 100 years after opening. The tracks between Bergermoen and Randsfjord were removed in 1984.
Today the line forms part of the Bergen railway route. Since the late 1980s, most Oslo-Bergen express trains run via Drammen and the Randsfjordbanen rather than the original route via Roa, even though the Drammen route is about 35 km longer. Stations along the line include Mjøndalen, Hokksund, Åmot, Geithus, Vikersund and Hønefoss.