The concept of building a direct tunnel connecting the Port of Miami with I-395 was first explored officially through a Vehicular Access Study commissioned by the City of Miami in 1981. At this time, the Miami-Dade Metropolitan Planning Organization (MPO) created the Port of Miami Access Task Force with a mandate of analyzing and identifying future bridge and tunnel access options to the Port.
Based on the Task Force's recommendations, the Miami-Dade County Board of Commissioners approved a three-phase plan to improve access to the Port of Miami in 1984. The plan included intersection improvements at Port Boulevard and Biscayne Boulevard, the replacement of the bascule Port Boulevard Bridge with a fixed-span bridge, which occurred in the 1990s, and the construction of a new direct access tunnel between the Port and I-395.
Following the approval of the plan, the FDOT began a Project Development and Environmental study to examine the environmental impact of bridge and tunnel alternatives in 1989. It released a draft environmental document assessing the effects of an immersed tube tunnel running in a diagonal alignment across the Main Channel between Watson Island and the Port of Miami in 1996. The analysis found that while the tunnel would be an effective transportation solution, the immersed-tube construction technique would have serious environmental impacts on Biscayne Bay and also disrupt operations at the Port of Miami.
Shortly after the release of the environmental document, the notion of using bored tunneling technology arose. The concept came to light at an industry forum exploring tunnel construction methods for a rail improvement in Miami. While that discussion was focused on another project, it proved to be pivotal for the Port of Miami Tunnel. After further analysis, FDOT ultimately decided to capitalize on advances in bored tunneling technology and construct the Port of Miami Tunnel as a bored structure. Given that this approach reduced the impacts of the tunnel on Biscayne Bay and Port operations dramatically, FHWA agreed to the change in May 1997. The project gained environmental clearance in November 2000.
Although the bored tunnel method had far fewer environmental impacts, it was extremely risky. In order to accommodate two lanes of traffic in each tunnel tube, the Port of Miami Tunnel would have the largest diameter of any bored tunnel in the United States. The size of the tunnel would be further complicated by the soft soil conditions below Biscayne Bay. In addition, while European contractors were familiar with the technique, no construction firms in the U.S. had experience with the technology.