59°39′53″N 10°36′47″E / 59.66472°N 10.61306°E
 Hurum entrance | |
| Overview | |
|---|---|
| Location | Oslofjord |
| Route |  European route E134 |
| Start | Måna, Frogn |
| End | Verpen, Hurum |
| Operation | |
| Work begun | 14 April 1997 |
| Opened | 29 June 2000 |
| Owner | Norwegian Public Roads Administration |
| Vehicles per day | 6,827 (2012) |
| Technical | |
| Length | 7,306 m (4.540 mi) |
| No. of lanes | 3 |
| Operating speed | 70 km/h (43 mph) |
| Lowest elevation | −134 m (−440 ft) |
| Width | 11.5 m (38 ft) |
| Grade | 7% |
The Oslofjord Tunnel (Norwegian: Oslofjordtunnelen) is a subsea road tunnel which traverses the Oslofjord, connecting Hurum and Frogn in Norway. Carrying three lanes, the 7,306-meter (23,970 ft) long tunnel reaches a depth of 134 meters (440 ft) below mean sea level. The tunnel has a maximum gradient of seven percent. It acts as a link connecting eastern and western Akershus county, supplementing the Moss–Horten Ferry which runs further south. The tunnel is since 2018 a part of European route E134, until 2018 it was part of National Road 23.
The crossing was originally served by the Drøbak–Storsand Ferry, which commenced in 1939. Plans for a fixed link were launched in 1963, originally based on two bridges which would connect to Håøya. Plans resurfaced in the early 1980s with the advent of subsea tunneling technology and the Oslo Airport location controversy, which proposed airports in Hurum, Ås and Hobøl. Even though Gardermoen was ultimately built as the airport, the tunnel had raised sufficient support to be built irrespectively. Parliament gave approval on 13 December 1996 and construction started on 14 April 1997. The tunnel was official opened on 29 June 2000 and was financed in part by a toll, collected by Bompengeselskapet Oslofjordtunnelen at a toll plaza in Frogn. In 2014, the manual toll station was replaced by an automatic station. Since 30 August 2016, it is free to pass through the tunnel.
The tunnel was flooded in 2003 and 2008 and experienced a landslide in 2003. All of these incidents resulted in the tunnel being closed for weeks. There have been two major truck fires, one in 2006 and one in 2011. After the latter incident, the tunnel has been closed for heavy traffic exceeding 7.5 tonnes. In an effort to eliminate the problem, the Public Roads Administration has proposed building a second tube.