The bridge-tunnel originally combined 12 miles (19 km) of trestle, two 1-mile (1.6 km) long tunnels, four artificial islands, two high-level bridges, approximately 2 miles (3.2 km) of causeway, and 5.5 miles (8.9 km) of approach roads—crossing the Chesapeake Bay and preserving traffic on the Thimble Shoals and Chesapeake shipping channels. The system remains one of only eight bridge-tunnel systems in the world, three of which are located in Hampton Roads, Virginia.