Posted on July 13, 2026
Submerged railway crossing between San Francisco and Oakland reveals a curious work of American engineering, formed by giant modules sunk at the bottom of the San Francisco Bay to create a transportation corridor hidden under the water and surrounded by seismic challenges.
One of the most impressive submerged railway crossings in the United States was born from 57 giant steel and concrete sections sunk at the bottom of the San Francisco Bay, in an operation that transformed colossal modules into a railway tunnel.
Used by the BART system, the Transbay Tube connects San Francisco to Oakland via tracks installed under the water, creating an underground metropolitan transportation corridor in a region marked by heavy traffic, unstable soil, and seismic risk.
Unlike a conventional tunnel fully excavated underground, the work was constructed with large modules manufactured on land, launched into the water, towed across the bay, and positioned at the bottom, within a trench prepared beforehand.
Each section was, on average, 330 feet long, about 100 meters, a dimension comparable to a football field, which helps explain the visual impact of such a large structure being sunk under the water.
