HOUSTON – Investigators believe a woman may have suffered a medical emergency before she crashed into an officer and died on I-45 North.

The crash happened at about 12:30 a.m. Monday near Crosstimbers, shutting down the freeway for more than three hours.

Police say the woman was in a maroon van when she hit the on-duty undercover officer’s pickup from behind. The van then hit a concrete barrier.

The woman, who was only in her twenties, died at the scene.

It’s possible the woman did not die from the crash but rather the medical emergency. Police say an autopsy is needed to determine the exact cause of the death.

The freeway has since reopened.