Lærdal Tunnel is the longest road tunnel in the world, it is a 24.51-kilometre-long (15.23 mi) road tunnel connecting the municipalities of Lærdal and Aurland in Vestland county, Norway. The tunnel extends the main European Route E16 by carrying two lanes that make up the final link on the highway connecting Oslo to Bergen. Construction started in 1995 and the tunnel opened in 2000, costing about 113 million dollars.
The Norwegian Public Roads Administration’s (NPRA) challenge was to design the tunnel so that people did not find the 20-minute-long trip monotonous, thereby losing concentration during the long journey. Experienced psychologists worked closely with NPRA to assess what would be the best solutions to these concerns. Simulators were used to find the best solutions as regards lighting levels and design and gentle curves and short straight sections make driving through the Laerdal tunnel less monotonous, without breaching the guidelines for safe viewing distance. At any given point in the tunnel, the safe viewing distance is 1,000m or more. The tunnel has been subdivided into four sections by means of specially widened areas. These sections are separated by three large mountain caves at 6-kilometre (3.7 mi) intervals. While the main tunnel has white lights, the caves have blue lighting with yellow lights at the fringes to give an impression of sunrise. The caves are meant to break the routine, providing a refreshing view and allowing drivers to take a short rest. The caverns are also used as turnaround points and for break areas to help lift claustrophobia during a 20-minute drive through the tunnel.
The tunnel does not have emergency exits. There are many safety precautions in case of accidents or fire. Emergency phones marked “SOS” are every 250 metres (820 ft) for contacting the police, fire departments, and hospitals. Fire extinguishers are placed every 125 metres (410 ft). In addition to the three large caverns, emergency niches have been built every 500 metres (1,600 ft).
The tunnel is longitudinally ventilated through only one ventilation air exhaust shaft, 18km from the Aurland end of the tunnel. About 10km from the Aurland end of the tunnel, a cleaning plant for the tunnel ventilation air was installed in a short side tunnel. This plant cleans the passing air and purifies it. The air quality in the tunnel is continuously monitored, and the air cleaning system automatically goes into operation when required.