The world's longest bridge-tunnel complex, the CBBT, solved the centuries-old problem of how to connect the southern tip of the Delmarva Peninsula (aka, Virginia 's Eastern Shore) to the mainland and the state's Coastal Virginia area, home to the communities of Virginia Beach and. The world's longest bridge-tunnel complex, the CBBT, solved the centuries-old problem of how to connect the southern tip of the Delmarva Peninsula (aka, Virginia 's Eastern Shore) to the mainland and the state's Coastal Virginia area, home to the communities of Virginia Beach and. The Transbay Tube is an underwater rail tunnel that carries Bay Area Rapid Transit 's four transbay lines under San Francisco Bay between the cities of San Francisco and Oakland in California. 8 km) long, and attaches to twin bored tunnels. The section of rail between. Transcontinental railroads have many bridge–tunnels. Boston's Big Dig created the Ted Williams Tunnel, reaching depths of 90 feet below the surface. Only in Virginia, though, can you find a record-breaking project that combines both underground and overground engineering elements: the Chesapeake Bay Bridge-Tunnel (CBBT). (Joseph Geha/KQED) South Bay transit officials in charge of building the $12. Underground chambers, often associated with a complex of connecting tunnels and shafts, increasingly are being used for such things as underground.