Port Miami Tunnel, Undersea road tunnel in Miami, Florida, United States

Port Miami Tunnel is a 4,200-foot (1,300 m) bored undersea road tunnel of two parallel tubes beneath Biscayne Bay, linking the MacArthur Causeway on Watson Island with PortMiami on Dodge Island. Its light-grey concrete portal carries incised capital letters, among them "NAVIGARE" and "NAVIGA," above two arched tunnel mouths; the right bore glows orange inside. The tubes pass under the Government Cut shipping channel, with their tops over 60 feet (18.3 m) below the seabed.

The idea of linking PortMiami to Watson Island was first raised in the 1980s to keep port traffic out of downtown Miami, then served only by a two-lane drawbridge. Federal study funding was included in the 1987 highway bill vetoed by President Ronald Reagan, and the project stalled until the City Commission approved it in December 2007. Cancelled in December 2008, it was reinstated in April 2009 after lobbying by Miami-Dade Mayor Carlos Alvarez. Construction began in May 2010; the tunnel opened on August 3, 2014.

The tunnel's name appears in the Latin inscription carved across the concrete portal, where words such as "NAVIGARE" and "NAVIGO" refer to sailing and navigation. The portal's two arched openings lead into tubes beneath Government Cut, the cruise ship channel, so drivers pass under vessels entering and leaving PortMiami.

The tunnel carries two side-by-side tubes under Government Cut, one for each direction, with two lanes per tube. It links the MacArthur Causeway on Watson Island to PortMiami on Dodge Island, letting port traffic bypass downtown Miami. The roadway was designed by Jacobs Engineering Group, with Langan Engineering & Environmental Services as geotechnical engineer.

The tunnel boring machine, 540 feet (160 m) long and over 40 feet (12 m) in diameter, was built in Germany, shipped to Florida aboard the cargo vessel Combi Dock I and reassembled on Watson Island. A naming contest run by the Girl Scouts named it Harriet. It bored two parallel tubes of 43 feet (13 m) diameter, each about 3,900 feet long.