The Follo Line (Norwegian: Follobanen) is a 22-kilometre (14 mi) high-speed railway between Oslo and Ski, Norway.

Between 1989 and 1996, the Østfold Line south of Ski to Moss was upgraded to double track and higher speeds.

To take full advantage of this and allow the rest of the Østfold Line to be upgraded for high speeds, it was necessary to increase capacity through the bottleneck from Oslo to Ski.

The Østfold Line between Oslo and Ski remains the largest bottle-neck on the Norwegian railway network.

Capacity on the upgraded double track from Ski to Moss cannot be fully utilized due to the limitations along the section from Ski to Oslo, and further growth in the number of freight trains along the South Corridor to Sweden and Continental Europe is impossible without reducing the number of passenger trains.

[10] Despite the existing double track all the way from Oslo to Moss, a further upgrade southwards will not be able to increase capacity past the current single train per hour to Fredrikstad, Sarpsborg and Halden.

The most optimistic plans involve finishing the first upgrades of track south of Moss simultaneously with the Follo Line.

The Rail Administration and Ministry of Transport is working on proposals for a high-speed railway between Oslo and Gothenburg in Sweden.

[12] A report from Det Norske Veritas published in 2008, and ordered by the Rail Administration, concluded that neither a station at Vevelstad or at Kolbotn could support the extra cost of construction.

[10] In 2009, the Rail Administration abandoned the plans to build the line via Kolbotn, stating that it was more important to secure a fast connection to Ski.

[10] The contractors Acciona from Spain, and Ghella from Italy, jointly signed the contract with the Rail Administration to build the Blix Tunnel in March 2015.

[25] The line opened on 11 December 2022 with the inaugural train to Oslo departed from Ski at 07:24 local time.

[16] With a new line, it is expected to have 11,000 more public transport trips through the corridor; this includes a 67% increase during rush-hour and 43% the rest of the day.

This allows a reduction of 5,800 car trips per day and reduces carbon dioxide emissions of 5,474 tonnes.

Until the Follo Line opened, there could not have a capacity increase on international freight trains to Norway.