The big-rig crashed from the eastbound direction into the highway's center divider at about 6:30 p.m., leaving the tractor on the divider and partially in the westbound lanes, the trailer in the eastbound lanes, and concrete sprayed into the road.
As of about 8:30 p.m. two westbound lanes and three eastbound lanes remained closed.
At least two other vehicles were involved, including a Chevy Tahoe that was towed as the driver was transported to a hospital. The extent of the driver's injuries and whether there were any passengers in the Tahoe is unknown.
CHP officers estimate that the road will be cleared by 10 p.m., but Caltrans may need to conduct repairs on the center median, further delaying the full reopening of the highway.
Traffic in the eastbound direction was backed up to the Bay Bridge toll plaza, and in the westbound direction drivers were delayed back to El Cerrito.
The trailer is full of mail, but no mail was lost in the crash.