Officers say a 31-year-old woman from Madera was driving westbound on Highway 198, approaching Akers, when she veered off the roadway and slammed into a center guard-rail just after 11 pm.
The driver was not wearing a seat belt and the crash ejected her from the car and onto the highway.
When first responders arrived, she was pronounced dead at the scene.
Detectives are looking into whether drugs or alcohol may have been a factor.