About 5 p.m., the woman was apparently shot two times inside the car and then dumped on the side of the freeway as the car was moving about, officials said.
Glendale Police Department officials said a suspect was in custody. He was injured from a self-inflicted gunshot wound to the upper torso and was rushed to the hospital.
The suspected allegedly fled the area and went south on the 2 Freeway before being apprehended.
"It was just two people in the vehicle," said Lt. Mark Rosson of the Los Angeles County Sheriff's Department. "We don't know if it was a domestic dispute. We don't know what the relationship is. It's not road rage."
Officials did not identify the suspect or the victim.