 Another planning office was established in 1962, initially led by Erik Himle. The final plans for the route were passed by parliament in 1968, and construction started in 1971. The main contractors were Ingeniør Thor Furuholmen, Dipl.ing. Kaare Backer, NSB, Jernbaneanlegget Oslo Sentralstasjon and Ingeniørbygg. Consultants included Ingeniørene Bonde & Co., Peer Qvam's arkitektkontor and the Norwegian Geotechnical Institute.
