The Fv553 between Karmøy and Tysvær crosses the Karmsund and the Førresfjord in tunnel. This is the T-forbindelsen, Karmøy's direct road to the mainland to the north, without the detour through Haugesund.

The tunnel opened on 5 September 2013, delayed from May to September that year, and was then Norway's longest undersea road tunnel, a title the Ryfylke tunnel took over in 2019. It has its own 1,164 metre arm up to the island of Fosen, and where the arms meet there is a roundabout inside the rock. In total there are about 9 kilometres of tunnel, and at its deepest the road lies 138 metres below sea level.

Before the T-forbindelsen, traffic between Karmøy and the mainland went via Haugesund. The tunnel gave the whole Haugaland shorter journeys, and it is today the main artery for commuting between Karmøy and Tysvær. When it closes the whole link stands still, so check the status before you drive.