Authorities suspect suicide, Bergenfield Police Lt. William Duran said.
The woman was struck by a northbound CSX train headed to New York State around 12:10 a.m. just south of the New Bridge Road crossing.
The locomotive stopped 300 feet before the Clinton Avenue crossing.
She was pronounced dead at the scene.
Bergenfield police responded along with CSX railroad police and representatives and the Bergen County Sheriff's Bureau of Criminal Identification, which collected evidence.
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