The Oslofjord Tunnel (Norwegian: Oslofjordtunnelen) is a subsea road tunnel which traverses the Oslofjord, connecting Hurum and Frogn in Norway. Carrying three lanes National Road 23, 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 the main link connecting Buskerud with Follo and Østfold, supplementing the Moss–Horten Ferry which runs further south.