2 ms·

The floating bridge idea is pretty interesting. I will say that here in Seattle we have deep experience. We commute on what is known as the 520 bridge, known by

by tomcam 4y ago

The floating bridge idea is pretty interesting. I will say that here in Seattle we have deep experience. We commute on what is known as the 520 bridge, known by the rest of the world as the Evergreen Point Floating Bridge[1]. It took close to 30 years and billions of dollars to reach 1.5 miles across the way. Conservatively it's something close to $3 billion per mile. Some of the pontoons still got cracked late in construction. [1] https://en.wikipedia.org/wiki/Evergreen_Point_Floating_Bridge https://en.wikipedia.org/wiki/Evergreen_Point_Floating_Bridg...

dredmorbius 4y ago
The concept would have more in common with the BART Transbay Tube, which itself is an immersed tube design, with a maximum depth approximating what might be necessary for a transoceanic floating tunnel: 41m (135 ft) below sea level, built in 57 sections. <https://en.wikipedia.org/wiki/Transbay_Tube https://en.wikipedia.org/wiki/Transbay_Tube> That cost $180 million (1970), just shy of a billion dollars in 2020, with actual structural construction (not including tracks and electrical) taking four years (1965--1969). Total length is 3.6 miles (5.8 km), so costs seem rather lower than the 520 bridge. The immersed tube doesn't float, which introduces additional considerations, but is similar in that components are fabricated offsite then assembled and connected at the site itself, usually on or just under the seabed or lakebed. <https://en.wikipedia.org/wiki/Immersed_tube https://en.wikipedia.org/wiki/Immersed_tube> That said, at $1b/3mi, a 3,000 mi link would run about a trillion dollars. It might of course be several times that. Comparing to commercial aviation: Wikipedia gives 44 one-way million transatlantic flight seats offered in 2015, citing The Transatlantic Market <http://www.anna.aero/wp-content/uploads/2015/06/150603-connect-transatlantic.pdf http://www.anna.aero/wp-content/uploads/2015/06/150603-conne...> At $500 per seat, that's $22 billion or so in annual passenger traffic, or a 45 year payback time based on a $1 trillion tunnel cost. Probably not a great prospect.

by tomcam 4y ago

dredmorbius 4y ago

The concept would have more in common with the BART Transbay Tube, which itself is an immersed tube design, with a maximum depth approximating what might be necessary for a transoceanic floating tunnel: 41m (135 ft) below sea level, built in 57 sections. <https://en.wikipedia.org/wiki/Transbay_Tube https://en.wikipedia.org/wiki/Transbay_Tube> That cost $180 million (1970), just shy of a billion dollars in 2020, with actual structural construction (not including tracks and electrical) taking four years (1965--1969). Total length is 3.6 miles (5.8 km), so costs seem rather lower than the 520 bridge. The immersed tube doesn't float, which introduces additional considerations, but is similar in that components are fabricated offsite then assembled and connected at the site itself, usually on or just under the seabed or lakebed. <https://en.wikipedia.org/wiki/Immersed_tube https://en.wikipedia.org/wiki/Immersed_tube> That said, at $1b/3mi, a 3,000 mi link would run about a trillion dollars. It might of course be several times that. Comparing to commercial aviation: Wikipedia gives 44 one-way million transatlantic flight seats offered in 2015, citing The Transatlantic Market <http://www.anna.aero/wp-content/uploads/2015/06/150603-connect-transatlantic.pdf http://www.anna.aero/wp-content/uploads/2015/06/150603-conne...> At $500 per seat, that's $22 billion or so in annual passenger traffic, or a 45 year payback time based on a $1 trillion tunnel cost. Probably not a great prospect.