The E39 between Sveio and Bømlo runs 7.9 kilometres under the Bømlafjord in Vestland. The tunnel is part of the Trekantsambandet, which tied Stord, Bømlo and the mainland together in 2000.

The tunnel was Norway's longest undersea road tunnel when it opened in December 2000. It reaches 260 metres below sea level. Before the link opened, Bømlo was connected to the rest of the country by ferry across the Bømlafjord.

The Trekantsambandet consists of three tunnels and two bridges. Together they gave Bømlo its first mainland connection, and removed two ferry crossings from the E39 at once.