Can we build subways underneath the ocean floor?

It's been done. The Channel Tunnel under the sea between England and France is probably the most notable example. It is a rail tunnel, though not what you'd traditionally call a subway. The BART (Bay Area Rapid Transit) in San Francisco passes und... read more

Nobody would build a railroad under water just for the heck of it. The Channel Tunnel was dreamed of for 200 years, and several previous attempts started, before it was finally achieved in 1994. It cost nearly $150 million per kilometer. read more

To a limit it has been done here in the Netherlands.. It is possible in shallow coastal waters. We can dredge up soil, or build polders. Just Google Flevoland and Maasvlakte. Building land in deeper ocean is next to impossible. You would be required to move amounts of earth, rocks, and concrete in the billions upon billions of tons. read more

A transatlantic tunnel is a theoretical tunnel that would span the Atlantic Ocean between North America and Europe possibly for such purposes as mass transit. Some proposals envision technologically advanced trains reaching speeds of 500 to 8,000 kilometres per hour (310 to 4,970 mph). read more