The way was cleared Thursday for construction of the oft-delayed Port of Miami tunnel project.

But don't expect digging to start anytime soon -- the machine to dig the tunnel hasn't even been built yet.

That process will begin soon after the private consortium awarded the project orders the machine from manufacturers in France and Germany.

Details about how the $1 billion tunnel will be built under Biscayne Bay between the MacArthur Causeway and the seaport have been known for some time, but they were fully outlined Thursday at the Florida Department of Transportation's West Miami-Dade office, where local and state officials gathered to announce the project's financial closing.

The step paves the way for the private consortium, Miami Access Tunnel, to proceed with fabrication of the tunnel boring machine as the next major milestone in a project that has been on the drawing board for almost three decades.

One of the project's goals is to draw cargo trucks, thereby easing congestion in downtown Miami. Trucks now clog downtown streets after exiting area expressways because there is no direct link to the seaport.

The tunnel would provide such a connection because it would amount to an extension of State Road 836, Interstate 395 and the MacArthur Causeway to the seaport.

``It's actually going to happen!'' an excited Miami-Dade County Mayor Carlos Alvarez told officials and guests. ``It's a day to celebrate. We can breathe a sigh of relief. It's a good day for Miami and Miami-Dade County.''

Alvarez stood as a veritable hero of the project, after personally rescuing it earlier this year when Florida Secretary of Transportation Stephanie Kopelousos had all but decided to scrap the deal and rebid the plan. Alvarez led a team to Tallahassee in April and persuaded Kopelousos to keep it alive.

A last-minute glitch in September brought the project to the brink of collapse again when the city of Miami failed to deliver a $50 million letter of credit on time.

It was finally delivered on Oct. 8.

Now Miami Access Tunnel can order the machine -- a giant device resembling one of those science-fiction contraptions capable of reaching the center of the earth.

The tunnel-boring machine will be 41 feet wide and tall and 480 feet long. Cost: $40 million.

But it will not arrive in Miami for at least 22 months. The machine must be tested, disassembled, shipped across the Atlantic and reassembled at the site where the tunnel will be bored.

The tunnel will run from the south side of the MacArthur Causeway at Watson Island under the 36-foot-deep Government Cut main shipping channel to the north side of Dodge Island, where it will emerge and link up with Port Boulevard.

The tunnel will consist of two tubes, each 41 feet wide and containing a two-lane roadway. The tunnel-boring machine will dig through soft limestone to a depth of more than 100 feet beneath the shipping channel, where cruise ships dock.

``The project is technically challenging,'' according to a Florida Department of Transportation document prepared for bidders and available on the project's website: www.portofmiamitunnel.com.

The machine's rotating circular cutting platform will bore through the rock, creating a round tunnel tube as it moves forward, while in the rear precast panels of reinforced concrete will be assembled to shape the walls of the tunnel.

According to officials, the first tube to be bored will run from Watson Island to the seaport. The second tube will run from the seaport to Watson Island. Each tube will take about six months.

Before tunnel work begins, workers will need to widen the MacArthur Causeway Bridge to accommodate tunnel traffic.

If everything stays on schedule, construction is expected to last 55 months with the tunnel opening to traffic by 2014.

Transportation officials have cited a tunnel construction price of about $610 million, though a press release distributed at Thursday's ceremony listed a design and construction price of $607 million. Other costs associated with the project -- such as operations and maintenance -- are expected to push the final bill to about $1 billion.

The state's share is about $457 million, followed by the county at about $402 million and then the city about $50 million. The state also will cover an additional $250 million for operation and maintenance costs over the three-decade-long concession to the low bidder, the consortium headed by French construction multinational Bouygues Travaux Publics.

The French firm has built dozens of tunnels, including the French portion of the English Channel tunnel.