The Transbay Tube Was Built at a Shipyard: How Oakland and San Francisco Became Connected Underwater

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

The Transbay Tube is often imagined as a tunnel dug continuously beneath the Bay. Its construction followed a different approach: large sections were fabricated on land, moved into the water and placed into a prepared trench.

That method connects two parts of the region’s history. San Francisco’s industrial waterfront helped build the infrastructure that would reshape travel between the city and Oakland.

The crossing began as separate fabricated sections

The Metropolitan Transportation Commission’s construction retrospective identifies Bethlehem Steel’s Pier 70 shipyard as the fabrication site for the tube’s 57 sections. It describes moving the sections by barge, lowering them into a trench and joining them on the Bay floor.

The construction approach moved much of the work into a controlled fabrication setting before the pieces reached their final location. Placement and connection then became specialized marine operations.

An immersed tube is therefore a distinct construction type. Calling it a tunnel describes the journey a passenger experiences, while the construction record explains how that enclosed route was made.

The structure was finished before passenger service began

The commission’s account records completion of the tube structure in 1969, followed by installation of railway and electrical systems. BART’s fiftieth-anniversary history identifies September 16, 1974, as the opening of passenger service through the crossing.

The gap between those milestones illustrates a common feature of transportation construction. A completed structural shell is not yet a functioning railway. Track, power, ventilation, controls and testing all contribute to making the route usable.

The commission also notes that BART’s initial East Bay opening preceded the underwater connection. The regional network familiar today arrived in stages.

Two trainways share a more complex internal arrangement

BART’s history describes two bores, each carrying a track, with upper and lower galleries between them for access, ventilation and utilities. The cross-section contains working space that an ordinary train passenger does not see.

This is a useful distinction between the passenger environment and the operating structure. The space needed to move trains is only part of the facility; staff access and supporting systems require their own routes.

The galleries also make the tube more than two hollow cylinders beside each other. Its internal organization serves several functions within one submerged assembly.

The route connects particular urban places

The anniversary account identifies West Oakland and Embarcadero as the stations at either side of the underwater journey. The tube links local station approaches with a regional crossing, turning separate neighborhood trips into a continuous rail journey.

For a resident, the significance is experienced at several scales. A walk to a station, the station’s circulation and a trip beneath the Bay are all parts of the same outing, but each depends on different physical infrastructure.

A familiar ride contains an industrial story

The shipyard connection makes the crossing especially local. Pier 70 was not merely a scenic place near the finished route; it supplied the large fabricated sections that became the route.

The story also explains why an apparently seamless trip can depend on many carefully connected pieces. The tube’s continuity is an engineering achievement assembled from separate elements.

Transportation history adds depth to a home search

Explore real estate and home for sale in Oakland and real estate and home for sale in San Francisco. Contact Diamond to compare homes through their actual station approaches, neighborhood setting and connection to the wider Bay Area.

Sources checked October 28, 2026. This construction history makes no current service-frequency, travel-time or structural-performance promise.