Jordan Steinke was sentenced to 30 months on supervised probation, after being found guilty of reckless endangerment and assault in July.
The 29-year-old was acquitted of criminal attempt to commit manslaughter.
Steinke lost her job over the incident and was ordered to perform 100 hours of community service.
The woman who was placed in the car, Yareni Rios-Gonzalez, suffered serious injuries in the crash, including a brain injury.
The incident happened in September 2022 when Steinke and another officer were investigating an alleged road rage incident about an hour’s drive outside of Denver.
Ms Rios-Gonzalez was pulled over, taken into custody and moved into a police car that had been parked on train tracks.
The officers were searching her vehicle when a train struck the police car.
In an apology read out to court during sentencing, Steinke said: “What happened that night has haunted me for 364 days.
“I remember your cries and your screams. I remember begging you to tell me your name. Praying that you would stay awake. I have never felt so helpless. We couldn’t get you out of the car.”
Steinke added that she hoped to give educational talks to police officers about the dangers of railway tracks.
Judge Timothy Kerns said he had planned to send Steinke to prison, the BBC reports, however he changed his mind when both the defence and prosecution asked for a probationary sentence.
The second now former officer involved in the incident, Pablo Vazquez, is due to go on trial later this year.