CTA train. (CBS)

CTA train. (CBS)

CHICAGO (CBS) — It’s the dirty little hidden danger of riding public transportation.

As CBS 2’s Roseanne Tellez reports, women who ride the subway regularly may know this woman’s story all to well.

“So it’s completely packed,” L rider Nicole Gelbart said. “I’m packed in like a sardine, and there’s a man standing behind me and something kept hitting my leg. I thought it was his bag.”

Then she realized he was aroused and not backing off. On a busy rush hour train, no one seemed to notice.

“I just tried to shift my body so he wasn’t touching me,” she said.

It was no easy task on a jam-packed train. She says she put her head down and counted the seconds to the next stop and exited the train.

Dr. Reginald Richardson says the behavior is called frotteurism–seeking arousal from unconsenting victims.

Alarmingly, he said it’s more common that people may think.

“I think most women I know, professionally and personally, have had at least one instance of this behavior,” he said.

So what should a woman do?

“This is equivalent to assault. So you draw attention saying very loudly, ‘Stop touching me, get away from me,’ ” said Richardson.

“These folks are generally not aggressive and generally will flee.”

Gelbart says she wishes she’d spoken up.

“I would have been proud of myself, but I just didn’t know what to do,” she said. “He’s going to get away with it and he’s going to do it on every packed train.”

The CTA, which received 44 reports of this type of behavior last year, offers similar advice: speak out or contact the train operator.

Dr. Richardson says this is really a mental illness and difficult to treat.

He encourages anybody with this type of addiction to seek help

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