Floating Bridges and Submerged Tunnels in Norway—The History and Future Outlook

To improve the efficiency of land transport, bridges, submerged tunnels and subsea tunnels are introduced to replace ferries to cross straits. For wide and especially straits with a large depth or very soft bottom, floating bridges or submerged tunnels are attractive. Modern floating bridges can be traced back to the pontoon bridge design implemented in the 1940s, and the notable Hood Canal bridge in 1961. More recent floating bridges include the two Norwegian floating bridges: the 845-m long Bergsoysund and the 1246-m long Nordhordland floating bridges built in 1992 and 1994, respectively. Submerged floating tunnels have been considered as an option for strait crossings, especially wide crossing such as the Gibraltar and Messina straits and the Hogsfjord in Norway. So far submerged floating tunnels have not been built, while immersed tunnels have been used in many places, essentially in relatively shallow water. Currently, the Norwegian Public Road Administration (NPRA) is assessing replacing ferries across 8 fjords by providing bridges or submerged tunnels on the Coastal Highway Route E39 Project. The width of the strait crossings is up to 5 km and the water depth is up to 1300 m. The NPRA is currently considering three alternative floating bridge concepts: curved, end anchored floating bridge or straight, side anchored floating bridge with mooring system and floating suspension bridge with pylons supported by TLP or spar floating bodies; as well as submerged tunnel type concepts. This paper presents an overview of relevant concepts, their characteristic behaviour and design criteria for serviceability and safety, especially dynamic response due to environmental and accidental loads, with a highlight on development trends.