The Dumbarton Bridge opened ahead of schedule Monday after officials originally planned to reopen it early this morning following construction work to bring the span up to seismic code.

The bridge closed late Friday night so a state-of-the-art  seismic joint on the eastern side of the main deck could be installed, Caltrans said.

The joint will raise the deck 5 inches and allow it to move 42 inches — 22 inches more than the old joint allowed — in the event of an earthquake. New barriers also were installed.

Additionally, the carpool lane on the approach to the westbound toll plaza will be used as another FasTrak lane only during noncarpool hours.