Emergency roadwork on the Richmond-San Rafael Bridge prompted a severe traffic alert Monday for both westbound and eastbound directions, which was expected to impact the afternoon commute, authorities said.

Caltrans said in a social media post just after noon Monday that maintenance crews discovered concrete on a portion of the bridge’s upper deck that was breaking up near the western end of the bridge. The discovery led Caltrans to close the No. 2 lane on the upper deck and the No. 2 and No. 3 lanes on the lower deck for repairs to the roadway. The No. 1 lane was to remain open in both directions.

Caltrans said the work to fix the roadway could take several hours to complete.

The agency and the California Highway Patrol said motorists should expect delays and seek alternate routes between Richmond and San Rafael.

In 2019, chunks of concrete from the bridge’s upper deck fell onto the lower deck in several incidents, some of which hit vehicles traveling on the lower deck. The incidents led Caltrans to replace dozens of expansion joints on the upper deck during a months-long project.

The Richmond-San Rafael Bridge was opened in September 1956 and built for $66 million.