THE WORLD'S LONGEST ROAD TUNNEL

This article reports progress in constructing the 24.5km Laerdal Tunnel on the E16 highway between Oslo and Bergen in Norway; it includes a route map. This tunnel is claimed to be the world's longest road tunnel, and it may also be one of the cheapest per metre to build. Its expected level of usage is low; it has a design capacity of only 400veh/h. Work on the project began in 1995, and the northern drive to the Laerdal portal broke through in February 1999. Breakthrough of the southern drive to the Aurdal portal is expected in September 1999, ahead of schedule, despite a tunnel face collapse there on 14 June 1999. The tunnel is scheduled to open in 2001. To improve safety, the two-lane highway through the tunnel has both straight sections and gentle curves to decrease driver boredom. Lights will be installed every 18m, telephones every 250m, and fire-fighting equipment every 125m. 12 video cameras throughout the tunnel will be linked to a continually open control centre. The tunnel is driven through hard gneiss, providing good tunnelling conditions for most of the route, but the high overburden, up to 1400m, produces high vertical stress and the danger of rockbursting. Excavation is by drill+blast, and there is a shotcrete lining. The ventilation system has a complex fan system.