The opening of the new eastern span of the San Francisco-Oakland Bay Bridge has been pushed back to at least December so contractors will have more time to fix failed bolts, transportation officials announced this week.

The $6.4 billion span, which will connect Yerba Buena Island to Oakland, was scheduled to open over Labor Day weekend in September.

The bridge also consists of a western span that connects downtown San Francisco to Yerba Buena Island.

The Toll Bridge Program Oversight Committee, which is in charge of project oversight of the Bay Area’s Toll Bridge Seismic Retrofit Program, announced the delay and released its investigative report into why 32 bolts broke on the new span of the bridge in March.

The committee is composed of the executive directors of the California Transportation Commission, Caltrans, and the Bay Area Toll Authority.

The report found that the steel rods failed hydrogen embrittlement—where metals become brittle and fractured following exposure to hydrogen. To fix the problem, the rods will need to be retrofitted with steel, which is estimated to cost $10 million.

“TBPOC will select a bridge opening date based upon the actual completion of east pier retrofit work, weather windows, traffic impacts and other information as it becomes available,” the committee said in a statement.

Construction on the new 2.2-mile-long East Span began in 2002. The new span is parallel to the existing east span, which will be demolished after the new span opens. The new span will include two side-by-side bridge decks, each with five travel lanes, and is built to withstand earthquakes.

Part of the Bay Bridge collapsed in the 1989 Loma Prieta earthquake, which was centered about 60 miles south of San Francisco and registered 6.9 on the Richter scale.

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