The accident happened near the 4600 block of North Kedzie in the Albany Park neighborhood.
Trains run across Kedzie Street Friday night but a few hours ago emergency crews arrived for a collision a car and a Brown Line train.
Thirty to forty passengers were escorted off the train and in the car was a female police officer.
"There was a lady coming out of the train to get out of the car. But she was pinned down. So I think somehow she got her loose and pulled her out of the window. I believe the door was jammed," said witness Joseph Abraham.
The officer in the unmarked vehicle was apparently in pursuit of a suspect.
"The chase went across the tracks here on Kedzie. The officer in the squad car tried to get across the tracks to assist her partner," said CPD Deputy Chief John Escalante.
The police officer's injuries are believed to be minor. The train operator was also taken to the hospital for chest pains.
"People don't realize the stress that does come with this job every day. And it's when you go across these gates like this, it can be a car, it can be a person. It can be anything," said Robert Kelly of the Amalgamated Transit Union.
The accident and resulting derailment caused commuting delays for motorists on Kedzie and CTA riders who were shuttled by bus around the accident.
"It would have been great if they would have told us downtown in the loop that this was happening," said commuter Doris Laser. "I could have taken the blue line to my husband's job and gotten on that way much faster."
The CTA Spokesperson says that they will review the incident and look at the video to see if there are any changes that need to be made to improve safety.
Also, the union president we spoke with says he recalls in years' past trains had to actually stop before crossing the avenue, but it's not clear if that procedure would have prevented what happened this evening.