Construction of the six-lane SR-520 pontoon bridge across Lake Washington in the US, has been completed.

Bicycle users and pedestrians are currently allowed to use the bridge, with motorised vehicles set to commence crossings at the end of April.

The US$ 4.6 billion bridge, which took four years to construct, replaces the 53-year-old original floating 520 bridge, and was built by Kiewit, General and Manson, as a joint-venture project.

The new bridge is built on 77 concrete pontoons, including 21 longitudinal pontoons, each measuring 110 metres in length and almost 23 metres in width and weighing around 11,000 tonnes.

The bridge is fixed to the lake bed with 58 anchors, the largest of which weigh around 450 tonnes.

Monitoring technology for the bridge includes ‘smart highway’ to monitor traffic levels and systems to detect leaks in the pontoons and assess wind levels.

Developers say the new bridge has a life expectancy of over 75 years and will be able to withstand sustained wind speeds of more than 143 kph.

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