Tromssantunneli is an underwater road tunnel that runs under the Tromsøysundet Strait, connecting the mainland with Tromsøya. The tunnel is part of European Route 8 and was opened in 1994. It has a total length of 3,500 meters for the T2 section and 3,386 meters for the T1 section. The tunnel reaches a depth of 102 meters below sea level and has a maximum gradient of 8.2 percent.
Tromssantunneli was Norway's only underwater road tunnel with two sections until 2010. It was built to improve traffic capacity, as the Tromsø Bridge became too small for the increasing traffic. The tunnel has thus played an important role in facilitating transport between the two areas.