The driver of a big rig that overturned and spilled oil after exiting southbound Highway 99 in Sacramento on Saturday suffered no injuries, according to Steve Nelson, a state Department of Transportation spokesman.

Caltrans crews responded to the accident about 11:30 a.m. at the 47th Avenue off-ramp, Nelson said.

The rig, which was transporting construction materials, blocked off-ramp and on-ramp access to Highway 99, he said.

Caltrans crews were able to contain the moderate oil spill that resulted from the accident and unloaded the construction material from the truck before being able to clear the rig, Nelson said.

The clean-up process was expected to take an additional two hours by about 3 p.m., Nelson said.

The California Highway Patrol is investigating the cause of the accident, he said.