Posey and Webster Street Tubes

Underwater tunnels in California

The Posey and Webster Street Tubes are two parallel underwater tunnels connecting the cities of Oakland and Alameda, California, running beneath the Oakland Estuary. Both are immersed tubes, constructed by sinking precast concrete segments to a trench in the Estuary floor, then sealing them together to create a tunnel. The Posey Tube, completed in 1928, currently carries one-way (Oakland-bound) traffic under the Estuary, while the Webster Street Tube, completed in 1963, carries traffic from Oakland to Alameda.

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