A big rig hauling an excavator and other tractor gear struck an overpass on the Riverside (91) Freeway in west Riverside Friday, hurling the excavator into lanes and damaging the span.

The semi ran into the Buchanan Street bridge over the eastbound 91 about 10:30 a.m., according to the California Highway Patrol.

The excavator, tied down in the rig’s cargo area, was ejected into the slow lane on the eastbound side, according to the CHP.

The freeway overcrossing sustained impact damage, but it did not appear to be deep, while both the No. 3 and 4 lanes also sustained surface damage, officials said.

The trucker was not injured, and no other vehicles were involved.

CHP officers briefly closed all eastbound lanes to remove debris, but the HOV, No. 1 and No. 2 lanes were re-opened within minutes. The other two lanes remained closed, and a SigAlert was issued at 10:42 a.m. because of the blockage.

The lanes were expected to be reopened by mid-afternoon.

Caltrans inspectors arrived shortly after 11 a.m. to examine the bridge for integrity and restoration requirements. It apparently remained open to traffic.

The excavator was towed away about noon.

CHP officers were investigating the cause of the accident, including why the trucker misjudged the height of his load.