FREMONT (CBS SF) — The Dumbarton Bridge reopened Monday evening after being closed for most of the weekend for construction work.

The bridge opened nearly 10 hours early, and was fully open in both directions by 7:30 p.m. It was originally slated to reopen at 5 a.m. on Tuesday and had been closed since late Friday night.

The construction work was part of an ongoing project to bring the bridge up to seismic code, Dumbarton Bridge Seismic Safety Project spokeswoman Effie Milionis Verducci said.

A major part of the project was the addition of a state of-the-art seismic joint on the eastern side of the main deck, which will replace the old one, Verducci said.

This joint will raise the deck five inches and allow it to move 42 inches — 22 inches more than the old joint allowed — in the event of a seismic event, she said.

This portion of the seismic retrofit leaves 10 percent remaining, which is expected to be completed in early 2013, Verducci said. The retrofit will increase the bridge’s flexibility and stability in the event of a major earthquake, she said.

Additionally, the carpool lane on the approach to the westbound toll plaza will be used as an additional FastTrack lane only during non-carpool hours beginning Tuesday morning, Verducci said.

Signs along the highway have been altered to match this change.

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