Follo High-Speed Railway Line, Oslo, Norway
 

Follo Line is a planned 22.5km (14 miles) high-speed railway line between Norway's capital city Oslo and the suburban town of Ski. The double-track line will run parallel to the Østfold Line.Construction on the new line is expected to begin in 2015 and be completed by 2021

This is a project to get better acces to east south of Oslo. This tunnel their building at Follo Line will be the longest railway tunnel in the nordic countries.
The tunnel will be 20 kilometers and like the first post 22 kilometers.

Today the local train towards ski use 34 minuts and others 22 minuts. With this new tunnel and tracks it will only be local train which will use the tracks they use today and the train towards Fredrikstad, Halden and Gothenburg will use the new tunnel, and that will also trains toward Askim and Mysen also. This trains will use from Oslo sentralstation to Ski only 11 minuts.

So this new tunnel wil open for much more traffic than we have today. Between Oslo and Ski there is no more than a single track. South of Ski at the western corridor we can find double tracks on parts of the Østfold line but the eastern corridor via Askim and Mysen is only single tracked. And the new Follo line is double tracked whole the way to Ski

The new tracks and tunnel will be open for trains in december 2022