Deep water structures NOT planned
The Transatlantic "vactrain" advocated by Frank Davidson (the founder and long time chair of the English Channel Tunnel project from start till completion), along with expert ocean engineer Ernst Frankel DOES NOT ADVOCATE DEEP WATER TUBES -- they advocate SFT "submerged floating tunnel" technology. They admit the horrific expense.
ET3 by contrast is NOT a train. The tubes are less than 1/3rd the diameter (less than 1/30th the cost) as "vactrain" tubes, and mostly will cross dry land (as most roads and railroads do). When ET3 must cross water, it could use SFT tech, OR more likely will be underground underwater (as the Chunnel is).
