The Nordby tunnel was opened in 1992 with a 2 tunnel courses, each with 2 lanes in the opposite directions. The tunnels has 5 technical rooms, of which 3 are located in the tunnel. The tunnel's total length is 3 850 metres.

Smiehagen tunnel was opened in 1999 with 1 tunnel with 2 lanes in 1 direction. The tunnel has a technical room that is located in the open air (above the tunnel). The tunnel's total length is 892 metres.

The work involves a complete renovation of Nordby and Smeihagen tunnels on the E6 in Follo. In addition there is approx. 6.6 km of work in open air zones (Nordby north — Ringnes, called Vinterbrosletta 2.1 km); Nordby south — Smeihagen 0.8 km; Smiehagen south — Korsegården 3.7 km. Portals and signs with the accompanying ditches shall be established in the open air zones.

The work shall primarily be carried out on 1 lane at a time, with traffic in the other lane. The work in the open air and in the tunnel shall mainly be carried out at night, with the exception of 2 closure periods of a total of 5 months.

The renovation of the Nordby and Smiehagen tunnel.

The expansion for 3 technical rooms in the Nordby tunnel, of which 1 350 m3 rock shall be removed by using wire sawing.

The expansion of 3 technical rooms outside the tunnels (open-air zones)

All electrical technical equipment shall be replaced:

— New ventilation systems in both tunnels.

Rock protection systems behind arches.

Fire protection measures in tunnel rooms and smoke protection measure for emergency ways.