By Dana Kozlov

CHICAGO (CBS)–Passengers who take Chicago’s “L” trains expect a platform to be waiting when the doors open, but that wasn’t the case for CTA Brown Line riders on one train Monday afternoon.

As the northbound train approached the Montrose stop, the doors opened, but there was no floor below.

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Passenger Alyssa Brody was on that car–the last car in the train–when she said she saw a passenger stop himself seconds before stepping off and falling more than 15 feet.

She said she heard him scream and jump backwards.

“It was terrifying,” Brody said. “The man was shaking and he was really upset and everybody was in shock.”

She said the operator, who has since been removed from his post operating trains, opened the doors well before the train stopped.

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The incident made her consider how dangerous it could be for other passengers, so she posted about it on social media.

At least four other people stated they’d seen it happen before, also on the Brown Line.

“I hope it doesn’t happen in the future because at some point not everybody is going to be as lucky as this gentleman was,” Brody said.

A CTA spokesperson said they’re investigating, but declined to say how many other similar incidents have been reported in the past.

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A CTA Board member also told Brody to report it.