Lanes on a major bridge connecting the San Francisco Bay Area were closed after chunks of concrete fell from the upper deck to the lower deck for the second time this year.

The California Highway Patrol posted an alert about the Richmond-San Rafael bridge closure shortly after 2 p.m. Friday.

Two lanes and a shoulder were shut on the eastbound side. They reopened after about an hour and a half.

It was not clear what caused the concrete to fall.

All lanes on the bridge were closed Feb. 7 after large chunks of concrete fell onto the lower deck.

The San Francisco Chronicle says despite the fact that the bridge has been forced to close twice in two months, the span was not considered structurally deficient by the American Road and Transportation Builders Association in recent testing.