How many pre-constructed sections are made on land?

M: Good evening! And welcome to the science show. We’ve heard a lot recently about extreme engineering. And one of the most amazing and astonishing ideas is a rail tunnel under the Atlantic Ocean, linking New York and London. With me in the studio to discuss this is Professor Massa. Welcome to the program, professor.
W: Thank you.
M: So, the first question, how would the transatlantic tunnel be built?
W: Well, it will be built in pre-constructed sections.
M: Urn, pre-constructed sections?
W: Yes, they would be made on land, and then put together under the sea.
M: Oh, how many of them?
W: Fifty-four thousand. They will be held in place by giant anchors which will be fixed to the bottom of the ocean. The tunnel will float 200 meters under the surface.
M: Amazing. And now as I understand it, the train running through this tunnel would be a magnetically levitated train, is that right? So what is a magnetically levitated train?
W: A magnetically levitated train, or maglev, isn’t like a conventional train. It doesn’t have wheels and doesn’t travel on rails. It travels in the vacuum between two magnets. The idea about it is an old one invented in Germany over seventy years ago.
M: And how fast does it travel ?
W: At the moment, a maglev train can travel at about 500km per hour. However, it will be possible for it to travel at 6,000km per hour.
M: Are you serious?
W: The journey from New York to London is about 5000km, and it will take 54 minutes.
M: How is this possible?
W: Well, ordinary trains travel on rails, so they can only reach a speed of around 300km per hour, and they are also very noisy. Maglev trains don’t use rails, so there’s no noise. There’s no pollution. The train would be fast, comfortable and quiet. The disadvantage is that the tracks should be specially built and they are very expensive indeed.
M: And will the transatlantic tunnel be safe?
W: Well, safety is the big problem. The ocean is very powerful, and the tunnel could be bent or cracked. Also a passing submarine or a drifting iceberg could hit the tunnel.