Katyann Marshall, 54, was killed around 9 p.m. after her vehicle veered off the highway at the Mamaroneck Road overpass and hit the highway sign, O'Leary said.
When police arrived on scene Marshall did not have a pulse. Officers performed CPR but could not revive her. She was taken to White Plains Hospital where she was pronounced dead, O'Leary said.
Witnesses to the accident said there didn't seem to be any other problems, such as issues with her car, he added.
"We believe a medical problem, not the crash, caused her death," O'Leary said.
The parkway was closed for several hours due to the crash.
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