10 of the longest floating bridges worldwide

Considered feats of modern engineering, floating bridges play a crucial role in areas where underwater conditions pose challenges for traditional bridge construction, either due to impracticality or high costs. Floating bridges, technically termed pontoon bridges, are innovative structures facilitating passage over water bodies where constructing permanent bridges isn't feasible. These bridges rely on pontoons or barges floating on the water's surface, especially beneficial in deep or soft-bottomed waterways.

In the following lines, 10 of the longest floating bridges around the world are presented:

1. The Evergreen Point Floating Bridge spans 2350m and is the longest floating bridge in the world. Situated in Seattle, USA, it was completed in 2016, serving as the passage for State Route 520 across Lake Washington. Supported by 77 concrete pontoons firmly anchored to the lakebed, it is engineered to endure the lake's depth and soft silt. The construction cost totaled $4.5 billion. The bridge replaced a four-lane structure that had been in use since 1963.

2. The Lacey V. Murrow Memorial Bridge is an innovative landmark in Seattle, USA, stretches 2020m and holds the distinction of being the first major floating bridge to employ concrete pontoons. The bridge opened for the public in 1940, and it facilitates traffic on Interstate 90 across Lake Washington. In 1993, after a catastrophic sinking incident during a 1990 renovation amidst a storm, underwent a reconstruction that cost approximately $93 million. This event prompted a thorough redesign and reconstruction effort that not only restored but also enhanced the bridge's infrastructure.

3. The Hood Canal Bridge is linking the Olympic and Kitsap Peninsulas in the USA and it spans 1988m over a natural fjord that flows into Puget Sound. Built in 1961, the decision to construct this bridge was influenced by the excessive expenses associated with traditional bridge support columns, considering the depth and muddy terrain below. Following damage from a windstorm in 1979, the bridge underwent reconstruction and resumed operation in 1982, while additional upgrades were carried out between 2003 and 2009.

4. The Guyana’s Demerara Harbour Bridge spans 1815m across the mouth of the Demerara River at the capital, Georgetown. The two-lane bridge built in 1978 facilitates the daily commute of approximately 14,000 vehicles but requires opening for river traffic, which can conflict with peak traffic times.

5. The Homer M. Hadley Memorial Bridge, built in 1989, is an essential component of Seattle's transportation system. It has a total length of 1772m and was constructed at a cost of $97 million. Ranked as the fifth-longest floating bridge globally, it was initially designed to accommodate bidirectional traffic during the renovation of its predecessor, the Lacey V. Murrow Memorial Bridge. As of present, it is poised to support the forthcoming 2 Line light rail, which is expected to start in 2025.

6. The Bergsøysund Bridge in Norway, has a length equal to 933m and it was completed in 1992. The bridge is linking the islands of Aspøya and Bergsøya over a fjord with a water depth of 320m. The engineering firm Johns Holt was responsible for designing the pontoons and abutments, while DNV Veritec designed the steel superstructure. The construction of the concrete pontoons was undertaken by Norwegian Contractors, and Aker Verdal was tasked with building the steel pipe truss superstructure. The bridge is supported by seven concrete pontoon foundations.

7. The Berbice Bridge in Guyana is extending 1571m and was completed in 2008. The bridge is spanning above the Berbice River mouth and comprising 39 pontoons. It allows for river traffic access for 1½ hours daily. The total cost of the project was $38 million.

8. The Nordhordland Bridge in Norway was completed in 1994. The bridge comprises a pontoon section spanning 1246m and is located near the city of Bergen, connecting the mainland to the island of Flatøy over Salhusfjorden, which reaches depths of 500m. It accommodates two lanes for vehicular traffic and includes a pedestrian/bicycle pathway. The floating segment consists of a steel box girder atop 10 concrete pontoons, each containing nine watertight cells. Moreover, the pontoons are secured using flexible plate connections, joined by bolts and tensioned cables.

9. The William R. Bennett Bridge, located in British Columbia, Canada, is measuring 690m in length and it was completed in 2008. The five-lane bridge is supported by nine pontoons, each 25m wide, ranging in length from 25m to 90m. The construction costs totaled 144.5 million Canadian dollars. This bridge replaced the three-lane Okanagan Lake Bridge, another floating bridge, which had been constructed in 1958.

10. The Yumemai Bridge situated in Osaka Bay is spanning 410m and it is the world's first floating swing bridge that links two man-made islands, Yumeshima and Maishima. The decision to adopt a floating bridge design stemmed from the soft ground composition of the reclaimed land, which made this approach more suitable. Supported by two large steel pontoons, the bridge features double arches. To combat corrosion, the sides of the pontoons are lined with titanium plates and equipped with a cathodic protection system. Weighing in at 30,000 tons, the floating segment of the bridge crosses the North Waterway, which sees infrequent boat traffic. During these instances, tugboats are utilized to maneuver the bridge.