The eastbound lanes of the freeway near the Tustin Avenue off ramp were closed for investigation but were reopened at 4:30 a.m.
The driver of the Mercedes, 21-year-old Anthony Fragoso of South Gate, had been traveling on the wrong side of the 91 for at least several miles before crashing head-on into a 2006 Scion xB.
The two people in the Scion, 26-year-old Alan Reyes of Diamond Bar and 24-year-old Vanessa Cease of Long Beach, were both killed as a result of the crash. A friend said the two had been dating.
Authorities said Fragoso appeared to be critically injured. He was arrested but was taken to an area hospital to be treated for major injuries.
It was unknown why Fragoso was traveling on the opposite side of the freeway. It's unclear if Fragoso was driving under the influence.
"In regards to the suspicion of any intoxication regards to alcohol or drugs, that has not been confirmed. However, it has not been ruled out at this time," said CHP officer Ray Payton.
Fragoso has been charged with vehicular manslaughter with gross negligence. Charges could escalate if tests come back positive for drugs or alcohol.