Societa Italiana per Condotte D'Acqua S.p.A. has selected Poyry to carry out rock and tunnel engineering for the Follo Line in Oslo, Norway. Poyry's assignment includes most of the design needed for 5.5 km of tunnels close to the city centre of Oslo, 4 km of which is for high-speed train traffic. The Follo Line connects Oslo with the city of Ski in the east-bound Follo district.

The Follo Line tunnel system will be the longest in Norway with a total length of 20 km and a maximum train speed of 250 km/h. Condotte is the EPC contractor of the part that Poyry is engineering, and the end client is the Norwegian National Rail Administration. The tunnel will be excavated using 'Drill & Blast' and 'Drill & Split' methods. All engineering will be carried out as Building Information Modelling (BIM).

The project includes some unique challenges, such as the existing underground facilities and the relocation of the underground river Alna.