The Monitor–Merrimac Memorial Bridge–Tunnel (MMMBT) is the 4.6 mile-long (7.4 km) Hampton Roads crossing for Interstate 664 in the southeastern portion of Virginia in the United States. It is a four-lane bridge–tunnel composed of bridges, trestles, man-made islands, and tunnels under a portion of the Hampton Roads harbor where the mouths of the James, Nansemond, and Elizabeth Rivers come together. The MMMBT cost $400 million to build, and it includes a four-lane tunnel that is 4,800 feet (1,463 m) long, two man-made portal islands, and 3.2 miles (5.1 km) of twin trestle.