The scale is different, but it’s far from a new idea. https://en.wikipedia.org/wiki/Immersed_tube#Examples https://en.wikipedia.org/wiki/Immersed_tube#Examples:

The scale is different, but it’s far from a new idea. https://en.wikipedia.org/wiki/Immersed_tube#Examples https://en.wikipedia.org/wiki/Immersed_tube#Examples: The first tunnel constructed with this method was the Shirley Gut Siphon, a six-foot sewer main laid in Boston, Massachusetts in 1893. The first example built to carry traffic was the Michigan Central Railway Tunnel constructed in 1910 under the Detroit River, and the first to carry road traffic is the Posey Tube, linking the cities of Alameda and Oakland, California in 1928. The oldest immersed tube in Europe is the Maastunnel in Rotterdam, which opened in 1942.