MIAMI -- Miami-Dade commissioners approved the most expensive public works project in South Florida history Tuesday.

The billion-dollar project would build a tunnel at the Port of Miami. It would go under Government Cut and connect the Macarthur Causeway and the port.

The causeway bridge would be widened by one lane approaching the tunnel portals on Watson Island. Two lanes of traffic would run in each direction beneath Government Cut.

The ambitious project will take five years to complete.

"The county's hard cap is $402.5 million," one commissioner said Tuesday.

The state of Florida was willing to chip in $600 million; that money would go away if the commission failed to act Tuesday, Local 10 reported.

"We need to do this. The money's on the table. The state's a partner. We got a good reputable international company," said another commissioner.

The French construction company referred to, however, has done business in Castro's Cuba, Local 10 reported, which gave some commissioners concern. But there was greater concern over keeping the Port of Miami competitive.

More than 5,000 trucks visit the Port of Miami every day, clogging downtown streets. The port tunnel would relieve the truck congestion by pushing the truck traffic north to the Macarthur Causeway and Watson Island."

The city of Miami still has to approve its share of the cost, which would amount to $55 million and some land.

The developer said construction could begin by late this year and the tunnel could be open by late 2012.