As the new Doyle Drive bypass went off this weekend without a hitch, important seismic retrofitting on the Golden Gate Bridge continues.

In order to make sure the orange beauty is in tip-top shape and safe for up to an 8.3 magnitude earthquake, workers have been replacing sections of the bridge as part of the seismic retrofit project.

Phase 3A, with a price tag of $125 million, is set to be finished soon. While underway, workers have been cutting out large gaping holes in the deck of the bridge for the past few weeks. At night, 10-by-25-foot segments of roadway are being excised and replaced with 78 new, 38,000-pound prefabricated segments trucked down from Napa.

The roadway on top of the anchorage house is also being replaced as part of the work. In case you aren’t aware, that’s the the box-like structure at the north end of the bridge where the cables that hold up the bridge end up.

GGB Chief Engineer Ewa Bauer told the IJ:

“When these pieces of roadway come up there is a big hole and you look down and see the inside of the anchorage house. It’s a long way down.”

This construction marks the first time the road over the anchorage house has been replaced since the bridge opened nearly 75 years ago.

The work for this phase started in February and Bauer expects it to be finished by the end of the year. Bauer said it’s no easy task to retrofit a bridge so vital to the surrounding cities:

“We are replacing the roadway piece by piece at night and each piece has to fit just right. A lot of planning went into this. We use lane closures, but we never completely close the bridge to traffic.”

Work started in 2001 for the three-phase bridge retrofit project. Work for the final Phase 3B is expected to begin next year with all work completed by 2018. Bauer said: