The California Highway Patrol issued a Sig-alert Friday afternoon after concrete once again fell from the upper deck of the Richmond-San Rafael Bridge onto the deck below.

The two eastbound lanes and shoulder in the eastbound direction closed at 2:04 p.m. as crews performed emergency roadwork. Bridge inspectors were also on scene.

All lanes reopened at about 3:40 p.m. and the Sig-alert was canceled.

Caltrans has scheduled overnight closures for the stretch of Interstate 580 to accommodate continuing repair work. According to 511, lanes in both directions will be closed from 9 p.m. to 5 a.m. over the next several months. One lane of traffic will be kept open in each direction.

MORE TRAFFIC TROUBLE: Northbound lanes of Highway 101 near Robin Williams Tunnel were shut due to big rig crash, fire

About two months ago, a similar incident forced all lanes of the bridge to close for hours. On February 7, large chunks of concrete fell onto the lower deck about a quarter mile west of the toll plaza. At first, just the lower deck was closed. Eventually, officials shut off both directions of Interstate 580 on the bridge as crews inspected the damage and conducted emergency repairs.

Despite the fact that the Richmond-San Rafael Bridge has been forced to close twice in two months, the bridge was not considered structurally deficient by the American Road and Transportation Builders Association in recent testing.

Read Alix Martichoux's latest stories and send her news tips at alix.martichoux@sfgate.com.

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