Governor Phil Murphy said Susan Brown died when her car collided with the Gladstone Branch train just before 6 p.m. near the Murray Hill Station in New Providence.
It is possible the car slid down a steep incline onto the tracks.
"We are not sure it was weather related," State Police Superintendent Colonial Patrick Callahan said.
Brown was extricated by local responders and taken to Morristown Medical Center, where she was pronounced dead.
There were 100 people on board the train at the time.
No injuries were reported to customers or crew.
The incident remains under investigation.
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