A US$ 1 billion tunnel project for the Miami Port Authority has been given the go-ahead following delivery of a US$ 50 million letter of credit to the Bouygues-led construction consortium.

The consortium, which won the US$ 659 million contract to build the tunnel earlier this year, will now order the giant tunnel boring machine (TBM) needed to complete the project.

The TBM is expected to take 10 to 12 months to build and will cost between US$ 20 and US$ 50 million.

The tunnel, which will take up to five years to complete, is expected to open in 2015.

Florida Department of Transportation (FDoT) officials said the 3 mile (4.83 km) structure - two 36 ft (11 m) diameter, two-lane tunnels - under Biscayne Bay will run from the south side of the MacArthur Causeway at Watson Island under the 100 ft (30.5 m) deep Government Cut main shipping channel to the north side of Dodge Island, where it will emerge and link up with Port Boulevard.

FDoT officials said the cost of constructing the tunnel is about US$ 610 million, but other costs associated with the project - operations, service and maintenance - are expected to push the final figure to about US$1 billion.

This will be shared by the FDoT, the city of Miami and Miami-Dade County, with the state paying about US$ 457 million, the county about US$ 402 million and the city about US$ 50 million.

The state also will cover the US$ 250 million for operation and maintenance costs over the 30 year concession period.

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