Construction on the tunnel, which will connect downtown to the port, is expected to last until 2014.
Proponents of the plan say the tunnel is necessary to give space to the large cargo trucks that travel between the two spots.
The cargo trucks will roll off the 836 expressway continuing east on the MacArthur Causeway and descend into a tunnel bored under Watson Island and deeper beneath the Government Cut Channel and emerging in the middle of Dodge Island in the heart of the Port of Miami. After dropping their containers, the rigs will return to the mainland through a companion northbound tunnel heading west on the causeway and on to the 836.
The project includes using a massive boring machine that will cut through the soil under the shipping channel and Watson Island. That phase won't begin until next year.
Each of the tunnels will be 41 feet in diameter and will dip to 120 feet below sea level. 400 workers will be on the job at the peak of construction.