An Oregon man repeatedly accused of assaulting women on Portland buses and trains has been barred for life from using the city's transit system.

TriMet, the transportation agency for the Portland metropolitan area, announced the "unprecedented" ban against Jared Walter, 32, in a tweet on Thursday.

"Today we took action to protect our riders. Based on the DA’s evidence, we gave Jared Walter a lifetime ban," the agency said. "Mr. Walter will be arrested if caught on our system. We've taken this unprecedented step because the safety our riders and employees is paramount."

Walter has been arrested at least 18 times for incidents that occurred on subways and buses, according to court to documents. It was not immediately clear what the status of all his arrests were.

His most recent arrest was in March after a woman told police that Walter sat behind her on the train and began "touching her upper thigh with his hand in her pocket," the Multnomah County District Attorney's Office said in a press release.

Court documents state that Walter has engaged in similar offenses over the past decade including "masturbating and ejaculating on TriMet passengers, cutting and super gluing their hair, and touching them inappropriately,” the district attorney's office said.

He was charged with harassment, sexual abuse and interfering with public transportation for the March incident. Jail records show that Walter was arrested on March 26. He pleaded not guilty and remains behind bars.