The crash happened just before 2:30 a.m. on westbound Highway 580 just east of the Central Avenue exit, near the Alameda-Contra Costa county line.
Witnesses said the woman was driving the wrong way on westbound Highway 580 when she crashed into a big-rig carrying a load of mail, CHP Officer Ralph Caggiano said. The truck was not a U.S. Postal Service vehicle.
The woman was pronounced dead at the scene. No other injuries were reported, Caggiano said.
The big-rig began leaking diesel fuel after the crash, and westbound I-580 was shut down for nearly five hours. At 7:24 a.m., the CHP reopened all but one lane. The lane was expected to be cleared at about 8:30 a.m.
Caggiano said it didn't appear that any nearby waterways had been polluted by the diesel spill.